In Part 1, "Disaster Comunications-Global" ( required
reading) we have discussed the problems facing a disaster or
aid team wishing to communicate with their office back in their
home country. In this part we will turn to the problems of communications
with and between members of the same team or group of teams in
an area of about 100KM or so around a given point. So how complicated
can that be? Well, it can be very simple if you wish, but also
there are some cases where a more complicated set-up is justified.
I will try to mention just about every practical system we at DRCF have ever heard of. Just because we mention (or don't mention) a system, this is not an endorsement of the idea. We merely acquaint you with the facts and leave you to decide what you think is best for you. Reading this won't make you an expert, but it will help you and your experts to come to a better understanding
The Disaster Relief Communications Foundation
(DRCF) is a Non Governmental Organisation (NGO),
a small registered charity, and we admit
that our resources are limited. However we do try most conscientiously
to make sure that what we say is generally agreed to be true,
or at least valid opinion, by experts in the relevant fields.
However if you know of something better that we do, we most sincerely
welcome input, for future revisions of the book.
Field telephones are ruggedised telephones often
designed to be left outdoors during use. Before you roll your
eyes upward and 'tut' at this section consider something. No lesser
organisations than the BBC, and most armies of the world still
use field telephone systems in 1996 though they could easily afford
radio systems. To see why, let's look at what a field telephone
system is and what its advantages over, say walkie-talkies
are.
An ordinary telephone system relies on power from a central switchboard
or Private Automatic Exchange
(PAX). This scheme is called the central battery system.
(CB).The problem is that if you lose the power to your switchboard,
you lose all of the phones. For this reason, though the BBC has
PAX telephones laid out in, for example, a commentary box at an
Outside Broadcast (OB) they do not totally trust to this system.
Engineers would find that when they needed it most, when some
kind of problem occurs, it would let them down.
An alternative system is called the Local Battery system
(LB). Incidentally this was the type of telephone first used by
the Edison Bell telephone system in 1876 or so. They are usually
distinguished by a rather comical looking crank handle sticking
out of the front or side. This handle is called the Magneto handle,
so the system is sometimes also called the Magneto system, though
more modern designs are electronic and have a button marked 'call'
or 'ring'. When the crank is turned (or the button pressed) the
bell on the other phone rings.
The phones are connected up by wires. Just about any
wire in existence is suitable, field telephones are not fussy.
Large reels of Jumper wire or field telephone wire are very cheap,
you can even use wire fences and an earth return . The phones
are totally self contained, they don't need power or any kind
of control system from anything else. This makes them very reliable
indeed. To power the microphone in the telephone, there is a built
in 3v battery called the polarising battery.
The very good news it that this battery can be just about any
disposable battery you can buy from anywhere, such as a bicycle
or torch battery, it is not special in any way and even the voltage
is not critical. They are switched on either when the phone is
lifted off the hook, or by pressing a button on the handset labelled
'press to talk'.
How long do the batteries last? Well that depends, but as a guide,
I have a collection of field telephones at home. My two boys age
5 and 3 play with them, and rather roughly. Not only have they
never been able to break them, but the batteries have to be changed
only about once per year, and only then because of ageing. I have
one phone which had the same battery in for 3 years, and still
worked perfectly straight from storage when it was needed.
Field telephones are tough and totally reliable. You will never
loose sleep over charging up the batteries every
8 hours as with a walkie talkie. In any case, you may not trust
your generator or mains supply enough to be sure
that there will be power to charge your radios, whereas the field
telephone batteries will work even when nearly totally flat, so
they won't let you down without warning. They are also immune
from interference and channel overloading, which often dog 'walkie
talkies'. Privacy is enhanced because listening in would involve
line tapping which is much more trouble to do without being caught.
This deters the casual listener who may be allocated the same
channel, or the person with a scanner.
Walkie talkies have the problem that if put
behind or inside a building or in a dip in the terrain, they will
not work. Furthermore, you may not get any warning of this until
you try and it doesn't work. Whereas field telephones will work
anywhere that you can get a cable to. The range of field telephones
is rather academic, but over 100km is possible. The limiting factor
will be how much cable you can bring to the site and have time
to 'string up'.
Report=Report
The St.John Ambulance Brigade provide the First Aid coverage for the London Marathon, an event which generates marathon numbers of First Aid cases. VHF channels became so overloaded with higher priority calls that there was hardly ever time for the information about dropped out runners to be sent to HQ for logging. Worried relatives would realise that their loved ones had not finished the race, and go to the St.John information point asking for the whereabouts of their runner. This information was available on a computer in another wing of the same building, (County Hall) but quite a long distance away. A temporary field telephone line was installed in about an hour, and soon the information could be passed in seconds from desk to desk.
Field telephones can be readily and cheaply purchased from Army
surplus or via magazines for about one tenth of the cost of a
walkie talkie. They are also simpler in that you will not need
a licence for them as they don't use a radio channel, neither
do the operators need licences.
With all these selling points, why does everyone buy Walkie-talkies?
The reason is , wires. The cost of wire of the type needed is
actually very little - that is not the problem, the problem is
the laborious task of stringing out the wires, a process called
'cabling'. This process does take some hours so
it is unsuitable for anyone constantly on the move.
Here we need to make a clear distinction between the cabling techniques,
each has its own style.
Temporary cabling is what your first response will be. This means
getting the cable from A to B with the least effort, therefore
the least time spent of rigging up. I can lay and fix one reel
of line (about 500m) in about half an hour in this way. Sometimes
you may just lay the wires on the ground, if out of the way of
footpaths and roads, and then use handy trees or buildings as
makeshift telegraph poles when a road crossing is required.
Inside buildings, the wire can be fed into a window and then loosely
tied to light fittings or taped to corners until a suitable position
for the phone is reached. The reliability of the link now depends
on keeping the line out of harm's way, so this is where imaginative
improvising comes in. The line will probably be broken a few times
while the best route is found, but the lines can be rejointed
without any special tools if this is the case.
If you do this in an urban environment, you must remember to look
out for adjacent power cables and never cable
over them, always well under. This is so that if your cable comes
undone at one of the verandas you tied it to, it will go slack
and not touch the power cable, maybe electrocuting the person
using the phone.
Despite being in a rush, you must take care to tie the line securely
over paths and roads to avoid trip or strangulation hazards. On
the other hand, you would want to use few enough knots that when
the operation is over, or if the phone's position is to be changed,
you can quickly reach and undo all the knots you tied, allowing
the cable to be easily reeled in without damage and re-used. Recovering
a reel of cable takes about half an hour.
Sooner or later someone is going to complain about the scruffy
wiring and the fact that they can't close the windows or doors
properly. Then you will have to smarten things up with a semi-permanent
scheme. This means tidying up the wiring by clipping or taping
it to the skirting board or door frames of the rooms. You may
have to drill a small hole in the door frames and window frames
to let the cable pass through unseen and let the doors close properly.
All of this will take much more time, about 1 or 2 hours per 100
m. You would do this when the line is established and the panic
is over, (unless there was not immediate panic in the first place),
in which case you should do a neat job the first time.
By the time the installation becomes semi-permanent and if the
line has to cross someone else's property, the owner will soon
complain if your wiring over or past his place is scruffy. Worst
of all, when the immediate crisis is over, the local officials
may complain about the wiring crossing public land and in particular
public roads, (on the other hand, seeing the state of some overhead
wiring in urban areas, no one may notice unless you are really
bad). If things have got to the stage that the locals can worry
about such things, then probably you can go home anyway, but if
you are in for a longer term commitment, then you can't expect
to do this for very long, and therefore field telephones will
be best used on your own camp, building, area of responsibility
or compound.
In many cases, where law and order has broken down, wire may be very valuable and so will be cut down and stolen for the copper. Even if the wire is not copper, they will cut it down and strip it to find out. This is a major problem in Africa for instance. Another problem is that in some countries, the government has a monopoly of communications of all sorts and so you will meet zealous opposition to unauthorised wires crossing public land.
If your installation is becoming more permanent, there is something
else you may find worth while, a Private wire.
If there is a telephone system in the town and if it is working,
you should naturally use the phone to call the other offices that
you need to contact. If the local phone system is not working
or is not reliable, or the waiting time for connection is very
long, you can make a special arrangement. In a 'private
wire' scheme, one of the telephone lines around the area which
would normally be connected to the local exchange, are diverted
between the points you specify. If there is spare local cable
capacity, then this is very easy and quick for the local engineers
to do ( the work will take about 2 hours once the administration
is out of the way). You can now connect your LB phones to the
wire and you have your own private hot line from point to point.
Your system will work even if the local exchange has failed, and
of course the line can never be blocked or busy.
Another good reason may be economy. Most companies charge for
Private wires on the basis of distance from point to point, a
fixed charge per quarter. If you make more than say four calls
to a nearby place per day, you may find it much cheaper to install
a private wire and LB phones, a sort of 'Hot Line'.
You can talk all you want now, it won't cost any more than the
fixed cost of renting the line.
These are private telephone exchanges. A Private Automatic eXchange
(PAX) means that you can
dial any phone wired up to the exchange, but not make calls to
any phone outside of your system. A Private Automatic Branch eXchange
(PABX or PBX)
gives the same service as a PAX, but in addition also gives access
to the PSTN. The advantage of a PBX is convenience.
Everyone instinctively knows how to use a phone, so no training
is needed for the users. The only major problem is typing out
a good directory and keeping it up to date, and the laborious
cabling needed.
=REPORT=REPORT=
This was the eventual solution
used in Beirut. Radio systems became hopelessly jammed
by poorly disciplined over use of the channels. Private individuals
started to install PBXs in their living rooms, then fan out a
spider's web of wires to any who wanted service. In time these
became connected together more or less informally and eventually
became connected to the PSTN by means of radio line extenders.
These systems are still the most reliable communication network
in the city at the time of my visit (1995) . The comical problem
is that users need several phones on their desk, one for the network
in each block they might need to communicate with.
You don't have to connect a PBX up to a PSTN line, but if you
do then this will give access to PSTN by any phone on the network.
If no PSTN lines exist in the area then you have the option of
providing one by satellite service, such as Vsat, INMARSAT,
or by a radio line extender. This means greater convenience as
users can share this resource without going to the terminal, which
can then be placed in a good position. Of course this will not
improve the reliability of the PSTN line, but perhaps you can
'leap frog' a broken Exchange and connect to a line which is working
better this way. HF radio Phone patches
can also be arranged, but a radio operator would have to operate
the radio, and a special phone patch system needs to be installed
on one of the extensions. This is the system adopted on ships,
for example.
Against PBXs, they depend on reliable power to the exchange. If
your exchange power fails, or the exchange fails, you will lose
all of the phones until service is restored. You will also have
the same problems as with field telephones, namely that you need
to carry out cabling to each and every phone separately. In fact
the situation is worse than with Magneto phones because you cannot
'daisy chain' on phone from another. You have to provide a separate
line to each phone.
PBXs vary in size and weight. DRCF has a 10 line PAX which is
shoe box sized and weighs 5KG, but some designs are quite large
and heavy. Older electro-mechanical designs are heavier but use
no power at all when on standby, electronic ones use the same
power whether idle or in use. It is unusual to find a design intended
for portable use. The laboriousness of installation and the non-agility
of PBXs means that they are best suited to longer term and shorter
range applications rather than fast response disaster communications.
It will take about half a day to install 10 lines, and when you
move on, it will take half a day to dismantle the system.
Cordless PBXs are like a small scale private
Cellular Phone system. In addition
to having wired extensions, there are also small, shoe box sized
'base stations' for mounting on the wall inside
or your building. The user uses special phones looking like cellular
phones. There are many versions of this, such as the international
standard Digital European Cordless Telephone (DECT)
system. The advantage is that because cabling is much simpler,
set up speed is much quicker. Also the users have the advantage
of total freedom within the coverage area of the system. My employers
use such a system at our office and I wouldn't go back to being
chained to my desk again at any price.
In fact the theoretical range is around 500M, but experience shows
that 300M is the best practical range provided base station site
is good enough (which is the critical factor). To cover a large area
may require the installation of many base stations. One per floor per
building is recommended.
Against them is the old problem of getting permission to use the
frequencies .The DECT system is unlikely to be affected by another
service, it is self-organising, but it would effect another existing
service on the same frequency. Also they are more expensive than
the wired line alternative, certainly much more expensive than
a VHF simplex radio system. If money is no problem, go for this,
but if it is then you have a hard task to justify it over 'walkie
talkies'.
The term 'Walkie Talkie' is a trademark of
the Motorola Corporation. Around the
late fifties very physically small valves were devised for fighter
aircraft, to the point where a radio transceiver could be fitted
into a box small enough to be carried in the hand. This was in
contrast to earlier designs which were microwave oven sized, and
had another ammo box for the batteries. To make them a bit more
user friendly, they cleverly designed them with cups at the ear
and mouth position so that they would automatically be used like
a telephone handset. They first saw use in the Korean war and
then later in the Vietnam war, when 'grunts' would direct helicopter
gunships to their positions with them.
Today, as with the term 'Walkman', or 'PC', which are really trademarks,
'Walkie-talkie' has come to mean a hand held two way radio system.
This history shows why experts curl their lips up when you say
walkie talkie, and prefer one of several alternative names. Englishmen
in particular hate to use the term, it sounds like baby talk to
their ears and you can see them visibly shudder when they hear
the words.
Here are some preferred names that you will hear in conversation
to refer to walkie talkies, and an explanation of where they have
come from and what they mean.
R/T or R/T set. This stands
for Radio Telephone. This term was invented to distinguish this
from a Wireless Telegraph (by morse code) in the 1920's, when
valves were invented and this made modulation practical. In Regulations
and laws, this is still what your set is called. In fact your
signals may be called' emissions by radio telephony' in your licence.
Today this term is completely obsolete because of the Public Land
Mobile Network (PLMN)
better known as the Cellular Phone system
or Mobile Phone system. Today the makers
of very small cellular phones make their terminals look like telephones
and indeed act just like them too. This is to help users to identify
with the concept , thus boost sales. You can see there is plenty
of scope for confusion with the term Radio Telephone, that is
why it is avoided these days (except by legislators).
Two-way radio. To many, the term 'radio'
means a wooden box with ornate fretwork standing in a commanding
position on grandads dressing table. This is actually a broadcast
receiver. The word 'broadcast' is borrowed from
a farming technique, where a farmer would sew a field by walking
casually around it with a sack of seeds in his hand, and literally
throw handfuls at random. This was of course very inefficient
and has been replaced by seed drilling. Radio programmes from
such organisations as the BBC are figuratively just cast out from
the transmitter, to land any which way they will, with no attempt
to control the reception at all.
Today, the meaning of Broadcasting in law is
that a signal is sent over an area without controlling the receivers.
There are special frequencies and laws covering Broadcasting,
so be very careful never to say that you are 'Broadcasting' from
your station, or the result could be an angry visit from a government
inspector wishing to close you down. Two way radio is an unofficial
but highly effective term by which laymen will not visualise Broadcasting.
P.R.set, Stands for Personal radio
set. This is a Police term because an individual radio is issued
to an individual PC for his care ( and he is answerable ). Many
people from a services or Private radio background use this term.
Portable radio. This means
it is designed to be used while carried in the hand. In contrast
to this term, a Transportable radio
means one which can be carried from place to place, because it
has handles on it and an internal battery, but is designed to
be placed on the table when in use. You may wonder why anyone
would do that if they had a portable set, but all will be explained
later. One thing to watch out for is that in law, there is no
distinction between portable and transportable, they both conform
to the same regulations. You must take care with some people that
they understand the difference between portable and transportable
equipment when talking about it.
CB sets, CB stands for Citizen's Band
and refers not to a type of radio as such, but to a set of laws
and regulations regarding their use. CB sets are technically just
like any others, but there are both advantages and disadvantages
to their use, which we will discuss later.
Amateur Radio or HAM Radio.
Again, like CB, this refers to a set of rules and regulations
and not to radio equipment as such. However there are some interesting
points about Amateur radio that need expanding on, so this is
another subject that we will return to.
Handie Talkie or HT, A new buzzword
used by many manufacturers and much beloved of the buzzword loving
amateur radio fraternity. A person using this word probably has
an amateur radio background, which is a good thing.
Handset. This really means the part
of an ordinary telephone that you hold against your ear. Someone
using this word is giving away that he has a background in Telephones,(which
is no bad thing). Some radios have 'telephone lookalike' handsets
instead of fist mics. This is good because it forces you to hold
the mic at the right place, and provides a clear sound right into
your ear.
Handheld. Good word.
Whatever its name, nearly everyone has seen or used a handheld.
Because of their small size, convenience and ruggedness, they
have found nearly universal acceptance by all serious organisations
who can justify the expense of them, they are a completely mature
product now, and modern designs are more similar than they are
different.
One off-putting thing about them is that it seems that no one
who uses them can resist the urge to speak fluent martian gobbledygook
when they pick one up. For some this is all part of the excitement,
and knowing your 'rogers' from your 'wilcos' is all part of the
rights of passage into the elite world of the airline pilots and
other glamourous folk, but for others it is at best a turn off
or at worst very intimidating. I have seen very intelligent and
articulate mature professionals reduced to stuttering wrecks for
fear of not incanting the right spells to make the thing work.
I want to tell you right now, that in most cases, ordinary language
is quite good enough. There are quite elaborate procedures for
some services such as Marine radio or Aeronautical
service, and they do help a great deal
when there is pressure to be clear and concise in the presence
of many languages. But if you are not planning to organise much
international air sea rescue on your handsets, don't bother.
There are however a few things you should not forget. First, unlike
a telephone, it will not ring when someone wants to talk to you,
so you must have it switched on all the time, and be listening
to the channel all the time to hear if a message is for you. Sounds
silly to say this, but we have come across cases where the system
was not working because users had their sets turned off, thinking
they would ring like a Mobile Phone.
Another point is that for historical reasons, most handhelds use
what is called the SIMPLEX system. The technical
details are not important but you can always tell a Simplex system
because of a button, or bar, on the handset labelled 'PTT'
or Press To Talk. You must hold down the PTT
all the time you are talking, and remember to let go when you
want to listen. Sounds simple but I have spent many frustrating
hours with highly educated people before this becomes instinctive.
You must say something when you have finished talking so that
the other person knows when to talk and when to shut up. Usually
this is done by saying 'over' before you let go of
the PTT, but anything that makes it clear who should talk next
is OK.
Don't forget that the Simplex system is a 'round table'
or 'party line' discussion, but for technical
reasons which aren't very interesting, only one person at a time
can talk. The usual way of fixing this is for the previous speaker
to clearly state who should speak next just before he says 'over'.
Another way is to have a person called the 'Net Controller'
to act like the chairman at a meeting, and decide who the next
speaker will be.
By the way, this apparently annoying side effect of simplex, that
all stations can hear everything said, is actually a great bonus.
If you keep an ear open to what is going on, it is like having
a rolling briefing constantly going on. In fact, sometimes someone
may just say something to no one in particular just so that everyone
can be informed, and understand the whole situation by the time
they are called personally for comment. This is one reason why
police, fire and ambulance services don't use mobile phones though
they could easily afford them.66
Just as every car needs a number plate, so every radio has to
have a Callsign, for the same reasons of tracking
and administration. One example of this is in aircraft. You will
see painted on every aeroplane, something like G-AVIR. This is
not the number plate of the aircraft but its radio callsign. To
avoid confusion if the line is a bit muffled, there is an agreed
list of words that stand for each letter of the alphabet, called
the international phonetic alphabet.
The words had to be carefully chosen so that every race and culture
could pronounce them and not get them confused. That is why a
pilot of the aircraft just mentioned would call up the tower and
say " Woodvale tower this is Golf Alpha Victor India Romeo,
taxi clearance".67
Why did I mention this when I promised you could use ordinary
language? The reason is that some administrations will issue
a licence on the condition that every message starts
and end with the callsign that they will decide upon. It will
be printed on the licence document. So you may get stuck with
"Lima Delta one five zero this is Whiskey Alpha three three
five" when you would rather say " Hello Fred this is
Bill, over". Your technical expert or administrator will
probably tell you what callsigns to use. Having said that, you
soon get used to it and I have many friends such as G0FTU, who's
name I can not always remember!
You will recall that I said that the other person you wish to
call should be listening to his radio. Actually this is not always
the case, and he may be holding another conversation or doing
something else just with the radio in earshot. You will first
have to get the attention of his conscious brain, make his 'ears
prick up', by what you say before waffling on with the question
you were wanting to ask. The best way is to call his callsign
and/or his name twice, then give your callsign and wait for him
to call you back. If he doesn't, then try again a few moments
later. You may say "Aidman one, aidman one, are you there
Brian? this is aidman two, over".
Because you have a virtual party line, you should obviously not
call until you have listened long enough to know that there is
not already another conversation going on. Simplex is a very unforgiving
one-at-a-time system and you will rudely bring the other conversation
to a halt ( unless of course your business is more urgent, in
which case, do explain this by starting with the words 'Priority!,Priority!'
or 'Break Break'). While you are talking, unknown to you, there
may be other users impatiently hopping from foot to foot saying
" get on with it you gas bag", so keep things as to-the-point
as possible, and always make it clear when you have finished the
conversation by saying something like 'over and out' or 'clearing
the channel'.
This is not an instruction manual but I mentioned these points
because it shows that you do need to think of training for your
users if you expect to get value for money for your handhelds.
Encourage your people to try them out, the moment of crisis is
too late for them to become familiar with them.
This is the favourite question for users and the most dreaded
one for the experts, who roll their eyes upward, draw a deep breath
and then don't really answer the question at all. To find out
why, lets take a closer look at our handheld.
The bulk of the handheld is probably the battery, in a clip at
the bottom. Then there is the transceiver itself, with knobs and
switches on it. Then sticking out of the top, is a part physically
small and unglamourous, but at least as important as the other
parts, a 'rubber duck'. This is actually not
rubber but a helically wound steel antenna
protected by a plastic outer sleeve. It happens that lower frequencies
need bigger antennas, so in fact, to make the antenna of a size
sensibly proportional to the radio, VHF or UHF frequencies are
used in handhelds. Otherwise you would end up with floppy fishing
rods which snag on everything and break the radio.
In theory a VHF or UHF radio signal has an infinite range, after
all, the astronauts on the moon in 1969 told us of their 'giant
leap for mankind' using VHF radios very similar to the handhelds
in use today. You are not in space, but on the ground, and if
I may make a point, quite close to the ground too, as many users
clip the handheld to their belt when not in use. It happens that
VHF and UHF don't penetrate through thick walls very well, and
not through earth at all. This means that the range is 'line of
sight' only.
You know as well as I do that this is not at all true, so what
is the explanation of the fact that UHF radio works so well in
built up areas when it should not? VHF radio waves have the property
that they bounce off objects they encounter rather well. UHF is
even better yet, so this explains why UHF is preferred for handhelds.
Imagine you lived in a chateau where every room was a copy of
the hall of mirrors, except that the mirrors where badly tarnished
and the windows nearly opaque. You can see that you could communicate
from room to room by a flashing lamp very easily, especially in
the dark. This is how the world looks to a UHF radio.
Now you can see why defining range is so difficult. You may have
a lucky spot at both ends and have a range of tens of kilometres,
but you may also get a disappointing few hundred meters. Finding
out what the range is, is a matter of trial and error. Every time
you change position, you should call up someone else to see if
you are in a 'dead spot'. Sometimes just putting the radio to
rest on a window shelf is enough to fix the problem, sometimes
a more elaborate solution is needed. In any case, regular radio
checks are a good idea as you will have no
warning when you or the other party does move into a dead spot.
Happily there are plenty of tricks for improving this situation
and we will now move on to explain them.
By now you realise that the secret is not in the electronics,
rather in the humble but very important antenna.
The simplest thing to do is to ask someone to talk for a few moments,
say count to 10, then move the radio around until the signal is
strongest. This may put the radio in an awkward position for speaking
into it, so an extension microphone can be used to make using
the radio more convenient.
of the Antenna |
If that doesn't work, you can try extending the antenna out of
the room altogether. This is only possible where the antenna can
be unplugged from the radio, or an extension lead can be plugged
in. An extension lead can then be plugged into the socket where
the antenna just came out, and the extension lead,
(specially made from 50 ohm co-ax cable and fitted with co-ax
sockets of the correct type and gender), can be lead out of the
room and to the highest point it will reach, (or the point with
the clearest view towards the place you want to communicate with).
However the extension lead will have some loss of signal, which
will get worse as the cable gets longer. In fact the cable should
be only about 100m long at the most, unless you use special (more
expensive) so called 'Low Loss' cable.
You cannot use the antenna that just came off your radio. You
must use a special design intended to work away from the radio.
However there are many good designs available 'off the shelf'.
Suitable models include, the dipole, the base loaded
whip, the ground plane radial,
the Slim Jim or the helical counterpoise whip and
very many more.
There are as many opinions as their are experts about which is
best, but the bottom line is that you are trading size and weight
for efficiency. Remember that you have to personally carry this
antenna on the 'plane and across rubble for days in order to fix
it up, the shop won't deliver it for you. I recommend the lightest,
easiest quarter wave whip with helical counterpoise, Ideally,
these should be supplied with a large, strong clip, so that they
can be quickly clipped onto a pipe or veranda rail, or failing
that, they can be taped into a good position or tied with string.
=REPORT=REPORT=
The St.John Ambulance brigade
use this technique at, for example, football grounds, where the
metalwork in the frame of the stands make handheld performance
very poor despite the very short distances. A small whip antenna
with a helical counterpoise is clipped to a position clear of
the metalwork, then a length of co-ax cable is led into a first
aid post, situated under a metal stand. An ordinary handheld radio
is then plugged in to the cable and powered by its own battery.
The results are always very satisfactory and the cost is a small
fraction of that of building a permanent base station which may
be used only a few times a year. With practice, a very satisfactory
antenna can be rigged up in about half an hour.
In any event, I can assure you that it is worth the effort, the
difference of even modest height is like night and day. The losses
in the cable are more than compensated for by the better antenna
position. The problem is that you have now sacrificed mobility.
You can easily use your ordinary handheld to connect to the external
antenna, no problem. There is then no security problem
as when the room is left unattended, the radio can be just clipped
to someone's belt and carried off. But as it will take a few
minutes to fix up the antenna again, you may decide to leave the
antenna fixed up in position until the location is no longer needed.
The next obvious logical step is to rig an external antenna system
up and leave the radio connected and in the room all the time.
This has the advantage that any user has reassurance that the
equipment will always be there when needed. However this is only
practical where security is assured, or there is usually someone
there. However if this is so, then the set-up could be in place
long enough to be worth investing some hours in siting the external
antenna in a really good spot. What you now have is a Base
Station, this is a theme to which
we will return later.
If you have a really good spot for your antenna, with a good view
over the area, then you are really on to something good. Whereas
individual handhelds may be out of contact with each other, they
could well be in good contact with you at your base station.
If there is someone at the base station, then they can write down
messages from one handheld, and repeat them to another, overcoming
some of the serious limitations with handhelds.
I want to stress here that the secret is in the position of the antenna, mostly its height, and not the power of the transmitter or anything else. A perfectly ordinary handheld connected to the antenna by an extension lead is just as good a base station as a more elaborate set up. However, there may be justification for something more elaborate and I promise to explain all as we go. I am going to come back to the subject of base stations, but now I think it is time to change subject to that of a Mobile station.
A rather funny name this, as mobile means moving and station means
not moving. The reason for this odd name is that the licence for
a radio transmitter is called in law a Radiocommunications Station
licence, so legally at least you have a mobile radio station.
A mobile station means that the equipment is mounted in a vehicle
and is designed to be operated while driving and on the move.
(or else it should be called Transportable).
I make no apologies for saying again that the important thing
is in the antenna. Vehicles have the advantage that weight
is less critical a problem so a much bigger and heavier antenna
can be fitted to a vehicle. The antenna will have a greater 'gain',
meaning signals will sound stronger. Furthermore the metal in
the vehicle itself helps the whole effect to be even better, but
this is only so if you install the antenna in a good position
and bond it well to the earth of the vehicle.
A further point is that as vehicles tend to be on the open road
and in clear open spaces more than a person is, then the range
of line of sight from the antenna is probably going to be much,
much more than from a handheld. Whereas a handheld
may give 2km range, a mobile can have a 20km range.
You don't have to have a permanently mounted radio in the vehicle
to gain these advantages. In the case of an emergency there may
not be time to install a mobile radio into the vehicle, or security
aspects may go against the whole idea. You can use a so called
'Magmount' antenna. This is a quarter wave or three quarter wave
antenna with a powerful magnet on the bottom. The antenna is mounted
on the roof of the vehicle and right in the centre of the roof.
It is held in position by the magnet, only direct brushing by
trees will dislodge it.
The feeder cable can then be let into an open window in the vehicle,
and an ordinary handheld can be connected to the magmount. The
radio can then be connected to the cigarette lighter of the vehicle
to draw power. This then gives the flexibility that you have a
charged handheld to use when you get out of the vehicle. You should
then disconnect the magmount, locking it up in the car, and connect
the rubber duck to the radio for portable use. This arrangement
is used by many radio amateurs for example, and is highly effective
and secure.
Up to now, I have been saying that power doesn't matter very much,
and antennas are the secret, but now I will have to say more about
power levels. As mentioned before, handhelds have
such poor antenna positions that the range will be limited more
by topography than anything else. Even though the signals do bounce
as I have said, there is a loss each time this happens, so the
signal gets weaker as it bounces each time to reach the other
unit. You might think the solution would be to simply raise the
power of the transmitter in the handheld, but there is a problem.
About two thirds of the size, and certainly the weight of a handheld
is its battery. This needs to be big enough to power
the radio until the user can get back to base and recharge the
battery. Recharging can take from 4 hours to
16 hours depending on the design of the charger, but usually the
battery in a handheld is designed to be used during a working
day of about 8 hours, and charged in the rest of the night. If
your day is longer than 8 hours then a better alternative is to
use batteries that can be unplugged from the bottom of the handheld,
and replaced with another one which was charged earlier. (obviously
you need to have enough chargers to charge both at night).
Actually if your battery does go flat, you may get no warning
of this and be missing vital messages , so in practice it is good
to change a battery about half way through the day, during lunch
break. This means carrying your spare battery
around with you to do this, or arranging a fresh battery for pick
up at the place you have lunch.
Handhelds use very little power when just listening on the channel
for a call, but very much more when the user talks. Typically,
a battery life may be quoted at 8hrs standby time (listening without
speaking) or 30 minutes 'talk' time, or sum of the two.
Therefore to make the batteries last longer, they would have to
be much bigger and heavier. The irony is that they would soon
get bigger than the rest of the whole handheld. There is only
one way to reduce battery size, that is to reduce transmitter
power.
However we have just seen that a mobile station may have a greater
range because of a better antenna, and thus because of that, it
will be worthwhile having a higher power transmitter. This in
turn will be possible because a vehicle battery has much greater
capacity than a handheld one, so the extra current drain is not
a problem.
We need to think of this at our base station. If you think you
will ever want to communicate with a mobile station, then you
should use a higher power transmitter at the base station, or
you may be able to hear the mobile calling you, but the mobile
won't be able to hear you replying. This is where your transportable
unit comes into it's own. Transportables have higher output power
than handhelds, so in addition to being larger, they also have
larger and heavier batteries. This is why the resulting unit looks
so ungainly. In addition, they also often have their battery chargers
built in to the unit. This is important because it will prevent
the all important charger being forgotten or put on the wrong
truck and sent in another direction (which has happened).
Transportables usually come with a rubber duck helical antenna built in, intended for use while on the move, but to use this when stationary would be to throw away the advantages of them. You should use a transportable in conjunction with a temporary external antenna, such as one that can be clipped to a fitting in a good position.
If you are in the happy position of being in a good spot all day,
then it will be worth while the hours it will take to put the
antenna in a really good spot and even use or improvise a modest
mast to improve the height. If you now have such a base station
you would be using it frequently to repeat messages for handhelds,
so you would perhaps assign someone to permanently keep an ear
on the channel at all times. However you may have the problem
that the spot which is good for a base station is not ideally
where staff would be in attendance at all times, so the site for
a base station may turn out to be a compromise between these two
factors.
By the way the term base station refers to the way you
use the site, not to the type of equipment installed there. You
do not have to install an imposing panel looking like Heathrow
approach radar to make it a base station. You may find that the
base station is a rather disappointing sight, a scrawny looking
radio rather like the one you have seen in the vehicle that brought
you. No matter, it is how it is used and where it is sited that
makes the difference, not what the equipment is.
=Report=Report=
The Lebanese Red Cross/Crescent
have to provide their own communications for the city of Beirut,
which was shattered by the recent war. They have their central
control situated in a high spot in the mountains just facing the
city, and thus are able to contact both stations in the city and
in Lebanon and Syria to relay messages for the Red Cross/Crescent.
They also pass personal messages of a humanitarian nature from
members of the public who hopefully submit desperate notes in
handwriting. (there is nothing else in most villages but the Red
Cross/Crescent radio). Impressed by how well this was working
I visited the base station, to find a small team of very enthusiastic
young volunteers, men and women, Christian and Muslim, bent over
a homely, improvised table with a dozen very ordinary VHF 'mobile
type' radios (apparently) haphazardly jumbled about. Hand written
notes in Arabic were being passed from one person to another with
speed and relayed on. They were a little embarrassed at the 'informal'
technology, but I assured them that they were doing much better
than some well equipped radio rooms I have seen, because of how
they were using their equipment rather than how expensive it was.
By the way, today they do have a splendid hi-tech control room,
but I hope the superb morale of the Lebanese Red Cross/Crescent
communications department is not changed.
One solution to the problem of having to have the Base Station
in an inconvenient position is a 'remote controlled' Base station.
In this arrangement, the base station itself is placed in a position
which is best for the antenna system. While
the controls are placed at a position where you can expect staff
to be present. This is done by using specially made basestations
which can be remotely controlled. There then has to be a cable
from the basestation to the remote controller. In most designs,
ordinary telephone cable can be used, then temporary cabling rather
like that used in field telephones can be rigged, enabling the
placing of the base station on the top floor of an adjacent building,
while the controller is in the office, perhaps at street or basement
level.
For a more permanent arrangement, a private wire
can be arranged from the local telephone administration, connecting
the two points. This will however cost you a installation fee
plus a quarterly fee for the maintenance of the line. This is
the method used by HM68 Coastguard and the Air traffic control authorities
among others. This explains their fantastically long reach as
they select towers on top of high hills for their basestations,
while the air traffic controllers headphones are connected to
them by telephone lines (private wires).
If a private wire is not practical, or there are not staff at
any location to handle traffic, then another alternative can be
tried. The repeater.
Usually called simply Repeaters or sometimes Relay Stations,
these automatically repeat messages just as the radio operator
would do at the base station, (if he were not having a break).
Naturally it does not do it by writing the messages down and speaking
them out but another way.
The receiver at the repeater receives the incoming message as
usual, but instead of putting the voice out on a loudspeaker,
the output is connected straight into the 'microphone' socket
of the transmitter. The receiver has circuits to detect when someone
is talking, and switches on its transmitter, boosting the signal
and putting it out of its own transmit antenna, (which is obviously
in the best position you can possibly find). The other handhelds
receive this strong signal from the repeater transmitter, and
so hear loud and clear signals from the sending handheld, giving
the impression that the handheld itself has a greater range. This
is the system used by for example police forces, which explains
why their handhelds seem to have such a good range.
However their are some snags with repeaters. For technical reasons
that I will have to explain later, if you set your radios to work
with repeaters, they then cannot work without them. Therefore
if your repeater is not working either because of a fault, loss
of power, it has been stolen, or it never seems to have made
the right truck somewhere, all of your radios will not work until
you fix your repeater.
Also, if your handhelds stray out of the area of coverage of the
repeater, say by driving to another town on the other side of
a hill, they will not work with each other, which will confuse
the users no end. If you choose to use repeaters you must guard
them with zeal. Someone will have to check them to change the
batteries or top up the fuel in the generator at least every 8
hours. You have just put all your eggs in one basket, so you must
take extra care with the repeater.69
Because of the vulnerability of repeaters, you will need to have
a fall back strategy, but in order to understand the problems
and solutions with them, I will have to get more technical about
channels.
Probably somewhere on your handheld or transceiver there will
be a control marked CH or Channel. Typically it will have some
positions marked A-B or 1-6. It may seem that contacting another
radio would be as simple as just selecting the right channel,
unfortunately this is not so and there are many complications.
To examine them lets just take a short step back and look at how
radio works.
In the days before radio, carrier pidgeons
were used to carry messages. When the pigeon arrived at the destination,
it was ignored. The important thing was the message strapped to
its leg. When radio first came in, the term carrier wave was often
used as an analogy with the pigeons. The carrier wave
transports the message to the receiver, where the carrier wave
is discarded and the message is extracted and read.
However, here the analogy ends. For one of the useful things about
radio, is that the carrier can be at various frequencies. A part
of the transmitter will set the frequency of the carrier before
the message is put on, by a process called Modulation,
in another unit called the Modulator. In the receiver at the other
end, a special part of the receiver called the Tuner,
can let in only the frequency wanted by the operator. The allowed
in carrier then has the message removed by a unit which does the
opposite to the Modulator, called the Demodulator.
If we set the tuner of the receiver to the same frequency as the
carrier at the transmitter, and if we use the same type of demodulator
as the transmitter had modulator, then the radio link will work.
Actually there is only one modulation system commonly used in
handhelds today, the FM system (12.5khz separation or 25khz separation)
so you would be unlucky to have a modulation system mismatch.
Frequency is another thing.
Apart from some exceptions which I promise to come back to later,
you will likely have applied to the host government in the country
you are operating in for a (PMR) or (Private Mobile Radio Licence).
You will then be allocated a frequency by the government, rather
than your choice. You may be lucky enough to have permission for
more than one frequency, but again, they will be set by the government.
To stop people illegally using frequencies for which they do
not have a licence, most governments forbid the use of radios
in which the user can select any frequency, but rather, specify
channellised equipment.
Prior to the introduction of Synthesizers, a crystal would be
fitted into the radio, one for each frequency used, by a technician
in a workshop. Today this is done by computer or diode programming,
but it means that the user can not select the frequency directly,
only select the ones fitted into his radio. There are several
problems with this.
One problem is that if your radios were programmed by different
technicians, they may have been programmed in a different order
to other sets. Therefore the frequency on channel 1 for one set,
may be channel 3 on another, and channel D on another. Never
assume different handhelds will work together until you have checked
every channel. If they don't work, don't assume that they are
not programmed, but test all channels until you know which are
which. The best thing is not to let this happen to you by carefully
controlling who programmes your radios and having some kind of
plan to standardise things. If you have the luxury of having the
frequencies written on a plate on the back of the radio, this
is better, but some organisations insist that the actual frequencies
be kept secret.
If you are working with a different organisation, then very likely
their sets will be on different frequencies to yours. There is
no point in saying, call me on channel two, because their channel
two may be a different frequency to yours. On the other hand,
if you are going to be working with another organisation a lot,
you will have to tell them the frequency of your channels so that
their engineer can programme their sets accordingly.
You would then need to arrange that the common frequency appears
on the same position of channel knob in the sets of both organisations,
as people are sure to say, 'call me on channel 2' rather than
'165.475MHz '. Interworking is not always
possible. Sometimes regulations or jealousy prevent this information
from becoming available so you will need to check that this is
OK before doing it. Sometimes the technical details of the radios
do not make it possible, for example if one organisation has VHF
and one has UHF.
There is a further complication regarding repeaters.
Remember I said that the repeater listens to a handheld then transmits
it out by its own transmitter. But this should be impossible because
the receiver would then become jammed by its own transmitter,
and never hear another word from the handheld. Quite true, so
a tricky trick is used. The transmitter puts the signal out on
a different frequency to the one the receiver is tuned to. This
is called the Duplex system.
The upshot is that the handhelds have to know to listen to the
output frequency, but when the PTT button is pressed, re-tune
to the repeater input frequency. Because the repeaters antennas
are usually higher than the handhelds, the repeater output frequency,
or handheld input is called the downlink. The handheld
output frequency which is the repeater input is called the uplink.
It would be too much to expect operators to remember all of this,
so the channel selector knob is programmed to arrange this automatically
when you select a certain channel number. So you can see that
some channels are two frequencies!
The bad news is that if the repeater were faulty,
or not put up yet, then the handhelds would not
hear each other because they would not be set to listen to the
transmit frequency of each other. There are two solutions to this
problem. The best one is to apply for a simplex
frequency in addition to your duplex pair. This
means that you manage without a repeater if you didn't have one
by simply changing to the other channel. The problem is that everyone
would have to know this and change accordingly.
Another idea is to programme one of the channels to the output
frequency of the repeater, but arrange simplex programming on
that channel. This could cause confusion because someone would
be sure to hear the repeater when flicking channel knob, then
wonder why no one could hear him when he calls. If you have only
one licence for one duplex channel , but have two channel radios,
then programme simplex mode on the downlink frequency. This has
the advantage that users can be warned to switch to the other
channel when the repeater's failure is learned of, because they
will still be listening to the downlink frequency in receive mode.
Again, you would need to explain what you had done to your users,
so some form of instruction is needed or your investment will
be wasted.
A further complication is that the government may not allocate
a duplex channel to you, in which case you cannot use a repeater.
In that case, you have the option of a remote base station arrangement.
Remote basestations also offer the advantage
that if they fail, handhelds that are in range can still talk
to each other, and to mobiles or transportables, so the problems
of working in failure mode are less severe.
Another problem with repeaters is that a handheld could quite
easily stray out of the area of coverage of the repeater. If the
area of operation is larger than the area of coverage of the repeater,
then another repeater will have to be built on a site suitable
for coverage of the new area. There are two problems with this,
firstly the users will have to know what the coverage areas of
the respective repeaters are and they will have to know of and
have their radios programmed with the frequency for the other
repeater. The other problem is that it is not possible to communicate
with users on the other repeater.
One solution to this problem is to couple or link the two repeaters
together, either by a landline link or by a radio link.
=Report=Report=
The USA Radio Amateur Civil Emergency
Service (RACES) have the privilege to do this. Upon a command
tone from a handheld station, the amateur radio service repeaters
will pick up and relay anything that the other one(s) in the same
group can hear. This results in the coverage of the handhelds
becoming region wide. -RACES
To overcome the problem of users having to keep re-tuning the
radios, more ambitious trunked radio systems are in use. With
these, the radio automatically scans for the strongest signal
and re-tunes to it. This does mean that the radio has to have
the appropriate control systems built in, and it has to be correctly
programmed.
In multi-channel 'pool' systems, each repeater station has not
just one channel, but several channel available for use. The same
repeater can then be used by different unrelated services, all
of whom benefit from the repeater's coverage. When a user presses
the push to talk button on the handset, a short data message is
sent from the handheld requesting an uplink channel to the repeater.
If there are no spare channels available at the repeater, then
the user hears a low pitch 'boop' sound, followed by a 'pip-pip-pip'
sound when a channel has become free and been allocated. When
the 'pip-pip-pip' has been heard, the user can now speak.
In the mean time, all the other handsets which are programmed
to be in the same group as the sending handset will have been
'paged' by the system, and will have tuned in to a downlink frequency
on the repeater who's service area they happen to be in.
More advanced versions such as the Ericsson/GE EDACS system are
digitally scrambled, making unauthorised overhearing, by journalists
for example, impossible. EDACS also offers the possibility for
a handset to 'join' and 'unjoin' groups as the needs requires.
For example, a Red Cross unit would be only in the Red Cross group
normally, but once on the scene, may decide to join the same group
as the local fire/police/medical services are on in order to co-ordinate
their efforts better.
The advantage of this is that there is virtually no limit to the
size of the area that can be served by such a system, while there
is no knob twiddling to be done by the user and so it feels just
like a simplex walkie- talkie to him.
The disadvantage is that 'ordinary' radios will not work with
a trunked system unless they are specially programmed to do so.
This means in fact that you have to be given radios by the operators
of the trunked network. This could present a problem as they
are quite expensive and so it is unlikely that there will be many
floating spares at very short notice.
Also, the system needs to be set up by engineers and so is unsuitable
for use in the first phase of a disaster. However it is ideal
for the case where regional planning policy provides for such
a system for the local emergency services, for instance. If you
are planning ahead for disaster communications in a known area,
try to get permission to use the local administration's trunked
network and obtain handsets and mobiles on their system.
Citizens band as it is called in the USA, UK and other countries,
refers to a band of frequencies which have special rules. Any
private citizen is free to go to the Post Office and purchase
a CB licence, renewable annually, entitling him to set up a radio
transmitter provided it conforms to certain rules. So far, this
is really not different to anything else mentioned above. The
result is that there is such a large mass market for sets which
conform to these rules, that the prices of the transceivers on
these bands tends to be about one quarter of that for any other
band. If cost is your priority, then this may be for you. However
there are some things that you need to be aware of.
For one thing, not all countries have a band allocated to citizens
personal radiocommunications, so it could be illegal to use them.
Some countries have their CB frequency band on a different frequency
to the 27MHZ used in the UK and the USA, so the price advantage
may be lost as cheaper equipment will not work. Additionally,
the USA specifies AM modulation whereas the UK specifies FM.
Another problem is the frequency itself. 27MHZ is a frequency
with big problems. Most of the time it acts like VHF, as a purely
line of sight mode, but not bouncing off walls of buildings very
well, reducing its effectiveness in built up environment. However
it does perform well at rolling over gentle and smooth terrain.
The problem is that due to the influence of the sun,
every 11 years it becomes liable to long distance 'skip'
causing its signals to bounce off the Ionosphere
and giving the band fantastic ranges. Well what is wrong with
that, you ask quite rightly? The problem is that now you will
have strong interference from USA and S America which will make
the channels hard to use for local messages as they will be swamped
by strong signals from excited (and illegal) high power stations.
A further problem is to do with the wavelength of 27MHz. It is
about 11 meters long, as opposed to about 70cm for UHF. This apparently
boring detail has a profound effect on antenna size. For example
external antennas have to be about 5 meters
long, making them much larger heavier and more expensive than
the titchy UHF equivalents. The biggest effects though are on
the handhelds. A whip on a handheld would have to be at least
2.5m long, like a fishing rod, in order to be efficient. Even
if you try helicals, the sizes become like horse whips and are
not really handy.
By far the biggest problem is the popular success of the band.
Many thousands of ordinary people, and in particular young operators
having their first taste of communications technology are on the
CB. As they are not required to pass an exam in procedures, this
means that discipline on the band is notoriously bad.
To add to that, many CB users feel that their band should be used
only for personal use, and greatly resent the use of the band
for 'serious' use. You can see why; commercial users would block
it all day with traffic that should really be sent on the proper
commercial frequencies set aside for that purpose. Therefore you
may find yourself subject to hostile 'jamming',
and a great deal of intimidation designed to make you move over
to a proper commercial frequency.
On the other hand, if you are operating in an area where a disaster
is in progress, CB users are unlikely to feel that way, and on
the contrary, you may find may useful local contacts who are in
a position to be of help to you . Nearly all countries supporting
CB have disaster relief networks such as 'React' to
help you in this way.
Whether legal or not, you may find that the CB band is the only
one which is common to all agencies working in some areas. We
saw before that interworking between agencies
can be fraught with technical difficulties, but you may have CB
in common with them, in which case the channels are the same frequencies
for both organisations. Unfortunately, repeaters
are forbidden on the band as duplex working is not allowed.
CB equipment is so relatively cheap that it is not a bad idea
to pack at least one transportable with external antenna, and
perhaps a handheld too, just in case it comes in handy. If it
doesn't, you can always use it for shopping trips.
Amateur radio, (or Ham radio)
is another set of international laws enabling private individuals
to operate radio stations for their own self training and entertainment(see
part 1, 3.4) In this respect it is like CB. But there are also
many differences, many of which are very important to know, so
without giving an exhaustive lecture about amateur radio, let's
look at some of the more important points.
Let me return to the theme of handheld radios again.
You will recall that some of the problems with CB are associated
with the large antennas and liability to jamming. Amateur radio
does not suffer from these problems because there are many frequency
bands allocated to amateur use, one of which is in the VHF band
and one in the UHF band, both of which are ideal for handheld
units.
Amateurs are required to sit an exam before being allowed to take
to the air, and are required to keep good behaviour or they risk
losing their licence. All of which adds to greater discipline
on the amateur radio bands. A further plus is that repeaters are
allowed on these bands, and furthermore, a large network of them
already exists.
Local amateurs are probably well drilled in the arts you need
for communicating in the local area. They will understand the
local topology, for example, and already know what is possible
and how. They will also know about the coverage of the local repeater
system and packet nodes. Even if you decide to deploy your own
system, Amateurs can advise you about what to deploy where and
even be able to help you with some of the hardware you may need.
Best of all, it won't cost you anything!
Another advantage is that the Amateur radio bands are defined
by international law, so you will have a common pool of agreed
frequencies to use for interworking with other
organisations. This has the advantage that there will be no need
to wait for a frequency to be allocated to you, you could start
to use the channels immediately.
With all these plus points, you may wonder why everyone does not
use the amateur bands. The reason is that in law it is strictly
forbidden for any person who does not have an Amateur radio licence
to operate on the band. So you would need to either take a Radio
Amateur with you, or get the users to obtain their own licences.
In practice the situation is much better. The International Telecommunications
Union (ITU) is very well aware of the practical problems faced
by disaster and aid organisations in moments of crisis, and are
also well aware of the benefits that radio can bring. In Resolution
640 (see 5.2), radio amateurs are encouraged
to 'meet the needs of international disaster communications'.
There is a full consideration of all this in chapter 5, but here
is a brief summary.
The British regulations, for example, say that a licensee can
allow a 'representative of a user service organisation' to use
his equipment, but only under his ' presence and direct supervision'.
As to what is the definition of a 'User service
organisation' and what constitutes 'direct supervision' depends
of the interpretation of the rules by the government in who's
territory you are working.
In the case of breakdown of authority in the area concerned, this
may provide you with a way of circumventing red tape and getting
equipment into the area as you won't be intruding on any existing
users frequency. This fact alone may be enough to allay fears
from existing users, and create less barriers to get you on the
air as soon as possible. Invoking resolution 640
provides you with a legal framework for operating, which will
keep you out of trouble, provided you obey the locally applicable
regulations but you must demonstrate absolute maturity in how
you exercise the privilege so provided.
It would be illegal to use the Amateur bands for an extended
period for a long term aid operation. Another point is that you
have absolutely no right to hog any channel, or to cause interference
to any other Amateur operator. Whatever the case, finding someone
in your organisation or team with the will to obtain an Amateur
licence is obviously no bad thing.
There are however security implications in using the Amateur service,
I have covered this before in part 1, but I thought this a good
time to repeat it again. The Amateur Radio Operators working with
you are unlikely to embarrass you, but many others will be listening
in with great interest. It will be like doing your laundry in
the town square, with passing strangers looking on. Ideally you
would like to solve this problem by using data systems
such as packet radio, in which case you would
want to scramble the data before sending. The problem
is that it is strictly forbidden for an Amateur station to send
messages in anything other than 'plain language'.
By contrast, your organisation rule book may insist that you preserve
the confidentiality of those you are serving, making passing such
information in such a public forum out of the question. This
issue means that the use of Amateur radio may be limited to logistical
matters, but in any case this will depend
on what the policy of your organisation, the policy of the host
nation regarding sending coded messages by amateurs, and how urgent
your need is.
A further problem is that amateur networks are designed to relay written messages from net to net until they arrive at their destination. It takes quite some minutes for even a simple message to be spoken over the air, written down, checked, and spoken again to the next net controller etc. until the message arrives at the addressee. If this requires, for example, four repetitions of the message, then it can take 20-30 minutes to ask a question and get a reply. Again, packet operation improves this situation.
Whatever we do, the range of VHF and UHF radio systems will be
about 50-100km at best, so what if we either don't have a high
spot to rig our antennas, or the range to the next base is more
than the range of our equipment?. One answer is HF Radio.
There is another better book dealing with the setting up of HF
radio stations for aid organisations, "Where There Is
No Telephone", (see
bibliography) so I will not repeat the fine work covered in its
material. However, while you are waiting to get your copy, I
will go over some of the main points.
For a fuller discussion of how HF radio works, see the Appendix
" How HF Radio Works". Basically we need to remember
that we are reflecting our signals off the underside of the ionoshpere,our
marvellous shield, protecting us from radiation in space and making
life on earth possible. However the shield is built to keep radiation
out, not radio in. It is different under the day part where the
sun is stronger and the shield is higher and more active, than
it is under the night time part where it is lower. As we rotate
under it, the frequencies that will work well by day will not
work well by night.
The bottom line is that you will need to have at least two frequencies
or more, (at least 2MHz apart), to give reliable HF radio contacts.
It then depends on the skill of the operators to decide which
frequency to use, but it is always better to use the higher one
by day and the lower one by night. The best thing would be if
we could get our experts to predict the best frequencies for us,
and then apply for licences at frequencies near
to the best ones selected by our experts.
The sad fact is that this will not be the case. We will have to
apply for a licence for a frequency from the government of that
country, but we will be just one of many applicants. The result
will be that we will be stuck using the frequencies that the government
issues. Therefore we may find that our frequency is only any good
at certain times of day, leaving us cut off the rest of the day.
If this is so, it is important to carry our regular radio checks
with the other stations in our organisations to see that they
are still in contact with us. Over a period of a year, the pattern
will emerge of how our network is performing.
Further bad news is that your licence may insist that you share
the frequency with other users, and specify a time for you to
use the frequency. If you are in a skip zone (dead
zone) at that time, you are out of luck, and should
re-apply to the government explaining your problem.
Whereas with VHF, the secret is the height of the antenna, in
HF radio, the secret is in the frequency you use. You should
get expert opinion about what frequency band to apply for.
frequency |
Once the licences are issued and their terms and conditions are
known, only then should the equipment be ordered and purchased.
The licence may specify certain technical restrictions on the
radios and antennas to be used, so you should get an expert to
look over the details for you before you purchase to make sure
that the equipment will meet 'type approval'. Type approval
varies from county to country, and is different from Europe to
Africa for example. Pester your salesman until you are quite happy
that the equipment meets the type approval for the country in
which it will be used , there are lots of bad stories about this.
See 3.1.3
The type of antenna you buy will depend upon the frequency you
are intending to use, the physical space that you have to erect
it and the range and direction of the other station or stations
you are intending to call.
There is more information on this in "Where There Is No Telephone"
and in part 1 CH 3.1.3 of this book, but here is a summary of
the main points.
Once the frequency has been decided upon (by the host government)
you now must specify this to the supplier of the antenna. If you
have been allocated more than one frequency, then it is possible
to have the same antenna designed to work with several frequencies,
in which case you must specify this to your antenna suppliers.
Another alternative is to use Broadband antennas,
or Long Wire antennas with an automatic
or manual Antenna Tuning Unit.(ATU).
Or you can use temporary 'bobbin type'
antennas which are physically wound out to the right size when
the frequency is chosen. This is better for those on the move
as it is very compact.
In any case you may end up with an antenna which is physically
about 50M long, so you may have to take this into account when
selecting antenna type.
If you are communicating to another place, the direction of which
is known, then a beam is better, concentrating your
power in that direction. If you are working mobile stations then
an 'inverted V' might be better, offering both vertical and horizontal
polarisation.
Good installation of HF antennas is very important, especially
with respect to their height, bearing and earthing.
Make sure that whoever installs the antenna has the instruction
manuals from the maker and has access to advice about the installation
of it.
The choice of make and model of radio is much less important than
the frequency and the antenna, but you should choose something
that your people can understand, and has a reputation for reliability
and prompt maintenance in your area and is type
approved in the country you are working in. One way of simplifying
things is to buy locally.
If you have been allocated more than one frequency, then a scanner,
allowing you to listen to the frequencies one at a time, at say
one second intervals, is a very good idea. Then if callers don't
get through on the higher frequency, they might try the lower
one. The problem is that if you don't know that the higher one
has faded out, you may be listening to a dead band without knowing
it.
Scanning receivers can be programmed
to switch from frequency to frequency so that you can listen on
all the frequencies that you may be called on. Naturally this
means that the calling person needs to make a call at least 15
seconds long in order for the scanner to visit that frequency
and open the speaker long enough for the person to recognise
his callsign. Separate scanners have to be connected in such a
way that they will be disconnected from the transceiver when transmit
is selected, by connection to an external RX antenna socket on
the back of the transceiver.
A much better way is to specify a transceiver which is capable
of scanning by itself, not all models offer this but it is highly
recommended.
The Amateur service can be used in a disaster, provided the Host
government has given its permission. By invoking ITU Resolution
640 and the Tampere convention, you can
use the HF radio bands allocated to the Amateur service ( see
ch 5). This will also solve the problem of interworking
with other groups in the area. Amateur bands in the 3.5, 7 and
10 MHZ band are all excellent for local contacts, but as usual
you must organise who listens to what frequency and when.
Amateur radio transceivers can be purchased which can also be
used in a general coverage mode and
thus be used both on amateur and commercial frequencies.
This will enable the same radio to be used for local calls and
for long distance phone calls via a coast station such as Portishead
Radio. Another important point is that
Amateur bands are not restricted to just voice communications.
Other more advanced data communication
modes are very common, indeed were developed on the Amateur bands.
To see why you would want to get an already complicated situation
even more complicated. Let's look at them on the next section.
There are many radio data systems, but by far the most common in 1996 are:
Before we look at them, we must ask, why spend time and money
on them when we can make do with something simpler? Perfectly
good question. Technical whizz kids just love gadgets, so they
are likely to insist on their indispensability sometimes for reasons
less than logical. Data communications systems will cost you more
to purchase. Not only because you will need special, (but not
too expensive) extra circuits, but because you will need a computer
or terminal to process the data.
Now, I have used computers every day for many years, in fact the
whole of this document was written on various lap top computers.
I would never be without one on my travels around the world, but
I still can't decide weather I love them or hate them. A fixed
desk top computer connected to the mains
is one thing, but when you start to travel with a computer it
is quite another. Is it robust enough to handle the bad knocks?,
did you remember to charge it? Where is the charger? Yes, computers
are not totally reliable yet. If your PC won't do the business
for any one of a hundred reasons, you will have egg all over your
very red face Trust me, I know.
Never trust techno-wizzgadgets. If you are really serious about
reliable communications, then always have a back up
plan, preferably a simpler system, to fall back
upon if your flagship sinks. For example you may arrange a voice
check on the link say two or three times a day
at a scheduled time convenient to both operators. If the data
system has failed, you will learn of this at the 'sked' and be
passed any missing traffic.
Now that I have said that, I still think that Data communications
systems are a very good idea, why? Because if they can be connected
to a regular radio, and if they are working, good. If not, then
you have not lost anything provided you take the kind of precautions
just mentioned.
=REPORT=REPORT=
In one recent case, a DRCF engineer
was sent on a very dangerous journey through a civil war zone
with a mission to find out why a Humanitarian aid communication
system was not working. The problem?, nothing wrong with the equipment,
but people were too busy to sit near to the radio all day, so
very often callers would call the station while no one was there.
Hearing no answer they assumed that there was a technical problem,
and having lost faith in the system, stopped using it.
Wouldn't it be nice if you could just write out a message for
the station at the other end at a printer on their
desk, or in their car. Then they could read it when they had time,
a kind of do-it-yourself Internet. Of course you
would want something that told you if the message got through
or not, but think, you could write your message and get on with
your very important work instead of wasting time with knobs, dials
and roger-wilcos.
You may smile and sigh at this fanciful dream from the far future
but don't. Its here now, it definitely works, and its relatively
cheap.
The Packet radio system ( I will discuss AX25)
is most suitable for VHF and UHF systems. It gets its name because
of the way it converts your data into 'packets' with an address
on the outside and the contents on the inside. You connect a small
box called a Terminal Node Controller (TNC)
to your ordinary radio's microphone and headphone socket, you
don't even have to open up the radio. Then you connect either
a computer or a 'terminal' to the box. Terminals can take the
form of a small thermal printer with a keyboard attached, such
as the famous TI703, or some portable electric typewriters can
be adapted for this job.
To use the system you just type "connect
station 1", for example into the keyboard. Then
it writes " connected to station
1". From then on anything you type comes out
at the other end on the screen or paper, perfectly simple. If
the other person is there at the time, you can even hold a two
way conversation. At the end of the message you type "disconnect"
and it replies "disconnected". There are many advantages
to having messages in text, and we have covered them in chapter
1.2.3 , so if you have not read that, please do so now.
You may wonder what if the station is out of range of your VHF
set. Normally, if you do not have a repeater, you
would be out of luck, but packet radio has another very pleasant
surprise up it's sleeve.
TNC's talents don't end at just connecting as in our first example.
They can also take in messages and then pass them on to someone
else who is in range of it, but out of range of the sender. This
is called Digipeating (digital repeating). Any
or all stations can be digipeaters. You can pass messages over
thousands of miles, if you know the routing to send it.
AX25 needs the sender to type in the route like this Connect
station 1 via station 5, then all is the same. However
some more intelligent systems can work out the routing for themselves.
If you are using digipeaters which are usually in the same position,
and which are normally switched on, then digipeating is ok, but
otherwise some other ideas are worth looking in to.
Suppose my equipment is out of range of the sender or the other
station is not always switched on, or I am a mobile station and
my route via the digipeaters is different from the usual, then
I won't get anything, so what now? The most common fix is to designate
one of the stations to be a mailbox. This will have to be one
which has a good power supply as a computer will now have to be
on all the time to act as a mail server, in
other words be running a special programme and preferably one
which is in a position of good radio coverage.
To send a message to the mailbox is also simple, the sender types
"send station6 at
mailbox1"
instead of the usual command. To retrieve messages, you just
connect to the mailbox via the digipeaters as usual, then after
typing in a password, you can privately read your mail.
There are many exciting ways of using packet radio, but this is
not an exhaustive manual on all modes so time to ask another question.
What if you are out of range of any VHF working digipeaters? There
are two methods, satellite systems, and the HF radio equivalent
of packet, TOR.
This system, called 'Satellife' (see appendix) was invented especially
for aid organisations by volunteer communications experts at Volunteers
in Technical Assistance (VITA). A packet radio
Digipeater/mailbox is built aboard a
Low Earth Orbiting Satellite (LEO).
The satellite passes low over the earth about four time per day.
You type your message into your TNC, then it waits until
the satellite passes over next time, and beams the message up.
At the same time, messages become beamed down by the satellite.
It is rather like a global roving mailman.
The plus side to this is that not only is the equipment very inexpensive
to purchase, but the service is free. The system has access to
Internet in order to traffic messages to users
not so equipped. There are more details about this in the appendix.
Teleprinter Over Radio (TOR)
can also be known as Simplex Teleprinter over Radio (SITOR)
or Amateur Microprocessor Teledata over Radio (AMTOR).
They are more similar than they are different.
In most ways, TOR is used just like packet radio is, but there
are some differences also.
There are in fact packet radio systems that work over HF radio.
These have the advantage that they can send the full ASCII character
set, making it possible to send messages generated by computer
mail programmes. However straight packet is much less reliable
over HF radio and so a special version called PAKTOR has been
developed and I will come to that later. For now we will stick
to TOR.
TOR is used in a way very similar to packet. The user first types
into the keyboard the receiving station's selective callsign,
then waits for a 'connected' indication from the terminal. From
then on, you can type out information that is guarantied to arrive
just as you typed it, on the other station's screen or paper.
This is achieved automatically, by sending the letters you typed
three at a time, and then checking that they are OK at the other
end. If they are not, then they are repeated until they are correct.
All this is done automatically so there is no need for the users
to know about any of this. A big plus is that it can work even
if the equipment is un-attended, thus freeing
people for more important jobs. Tor is very mature now and is
used by such organisations as the CICR(Comitee International Red
Cross). There are also mailboxes
available for TOR just as there are for packet.
The disadvantage of TOR is that for reasons of history, it can
only transmit letters of the alphabet, numbers and a few punctuation
symbols. You can therefore not transfer ASCII coded
computer data over it directly, but of course programmes exist
for filtering out unsupported characters, if you do write the
message on a computer and forget.
The Pactor system is a highly successful development from the
TOR systems just mentioned. It took the best of the TOR and Packet
systems and combined them into one. It was invented by a group
of German radio amateurs who wanted to exchange computer data
files and found the limited character set of AMTOR
too restrictive for their liking. There are three big advantages
of Pactor.
1) It can transmit the whole ASCII character set,
in other words upper case and lower case letters, and can transmit
all of the symbols appearing on your computer keyboard.
At first this may seem like only a small victory, but it means
that pactor can carry files generated by electronic mailing systems,
for example. Another less obvious advantage is that it can transmit
computer files which are not messages at all, such as spreadsheets,
or even programs themselves.
2) It transfers data much faster than TOR, four times faster,
at a rate of 200 Bauds for Pactor as against 50 for TOR. there
is also a version transferring data at 800 Bauds. (However this
is still reletively slow compared with PSTN line and modem).
3) More advanced error correction systems
are used so that the chances of the message arriving without corruption,
even over a bad circuit, are better.
The Humanitarian aid community soon showed interest in this mode
and a special version was developed for them, known as Swiss-PTC
(Pactor Controller). It was a big hit and generated high demand
for traffic. It is not exactly the same as normal amateur pactor
in order to discourage unintended listners from copying information
not intended for them .
=Report=Report
In one case, a journalist
was 'listening in' to SITOR signals across a Red Cross frequency,
using AMTOR equipment, when he intercepted some private
remarks from a Red Cross field team intended for internal use
at the Red Cross HQ. He illegally used the contents of the message
he had intercepted to write a newspaper report
which was so sensational that it caused a big diplomatic incident.
The result was huge costs to the Red Cross, due to the cost of
relocating the persons mentioned in the article. Though Humanitarian
aid organisations are hardly the CIA, they do work in very tense
environments and so there is always the need to prevent messages
getting into the wrong hands and being taken out of context, not
to mention mischievous use of information by unscrupulous journalists.
To improve speeds still further took much more effort from the
experts. More advanced modems and dedicated data coding chips
were then added to the system in order to develop a faster and
yet more reliable system which would have a speed of 800 Bauds.
However with so many stations already using pactor and Swiss
PTC, it was arranged for the new system to automatically recognise
the correct system and select that one, while remaining compatible
with ordinary SITOR as well. The new system became known as PTC-2.
Pactor is now the favourite system for use by Humanitarian aid
organisations at time of writing in June of 1996, and such as
the ICRC, IFRC, UNHCR etc. use
it as standard. In fact it is part of the IFRC automated electronic
mail system. It enables Red Cross
offices in areas where there are no data services, to access the
electronic mailing system in Geneva and all without
the aid of radio operators in the radio room. The main advantage
is that, because the Red Cross have private frequencies,
there are no costs to pay other than the first cost of the equipment.
Continuous Tone Controlled Squelch System (CTCSS)
is offered on most VHF and UHF sets. It often happens that you
have to share a frequency with another user, and their constant
chatter is bothersome to listen to, leaving you to turn your volume
down so low that you can't hear your own people calling you.
In a CTCSS scheme your sets emit a continuous tone while the PTT
is pressed, but this is not heard in your loudspeaker. Instead,
a circuit inside your set checks to see if the signal is one of
yours, and if so, switches on the speaker. If not, then the speaker
stays silent and your nerves are spared.
There are however some rather disturbing down sides to CTCSS.
One of them is that if you recall, only one user at a time can
use a frequency, so how can you tell that another user is not
on the frequency? You can't, neither can they. They might be blasting
across your calls and wiping you out without knowing it, and you
likewise.
Hopefully they are fitted with a system which will not let them
transmit unless the channel is not occupied, but if you are also
so fitted, there is potential for a problem. If you press and
talk, but the channel is occupied, you will transmit nothing but
think you are transmitting. Actually there will be a light or
beep indication on the control panel of the radio, but will all
of your people think of that? They might either think a message
has got through that hasn't, or lose faith in the system when
it doesn't work.
=Report=Report=
The volunteer St.John Ambulance
brigade in London, England are
a front line ambulance group. They supplement
the London Ambulance Service and are often faced with a busy day
of calls from the public, needing vital life saving assistance
at once. The Ambulances are dispatched from the HQ near Baker
St., in the west end of London, by simplex radio system
in the VHF band. Suddenly without warning, a very powerful station,
callsign 'Zero Base', started to come on the same frequency
as was used for ambulance dispatch. It often happened that urgent
messages to ambulances were lost, garbled and delayed when this
new station just transmitted across the weaker ambulances. Pleas
to the dispatcher of the intruding station were ignored. In time
it was discovered, by St.John engineers, that a private security
company had been allocated the same frequency as the brigade,
but were using CTCSS in order to have 'privacy'.
CTCSS does not give real privacy and you must understand
what is actually happening when you use it.
A further problem is, suppose another organisation needs to contact
you urgently and tunes to your frequency expecting to contact
you. You won't hear them unless they also know of and have programmed
in the CTCSS tone.
Frankly I think it isn't worth using CTCSS in simplex mode given the problems, unless the interfering stations are always weaker than yours.70 However it is used by the UNDHA for example in their repeater systems. We must make sure that our repeater will not pick up random interference (of which there may be plenty) and block our repeater by holding it in the transmit position. By using CTCSS, the repeater will only open when our mobiles are transmitting. The repeater downlink should be stronger than any adjacent signals so the problems are much smaller than the advantages.
it is an illusion. You cannot hear other stations on the same frequency, but they can easily hear you. |
Selective Calling (SELCALL) is another scheme to overcome the
problem of having to listen to other people's chat. There are
various methods of it but the basic idea is the same. Each station
has a built in circuit board with a unique code. Only when the
code is heard will the speaker be switched on. The sender of the
message must first send the SELCALL code before trying to call
the other station. SELCALL produces a very distinctive sound,
like dyslexic pan pipes.
There are however two features that SELCALL offers that are different
from CTCSS. One is that you can call all or only one station.
You can arrange it so that when the SELCALL is received, a bell
sounds in the building or the horn sounds on the vehicle. This
could alert the staff to an incoming call without them having
to be in earshot of the radio at all. Another feature is called
revertive calling. With this, you will
get an indication of some sort at the sending end if the receiving
station received the code and has set off its alert horn. This
can give you reassurance that the system is working.
However there is also a problem with SELCALL. It often happens
that key leaders are doing more than one job in on going emergency.
Suppose for example that the Duty officer has the SELCALL 101.
When you call this SELCALL his personal radio and only this one
will switch on. This is fine if he is carrying that particular
set. Suppose that same person is also acting as first officer
of the Disaster Action team at the same time. To call the First
officer the SELCALL would be 102, for example. This would mean
that the officer would have to carry both handsets in order to
receive both calls. The situation would become more complicated
if he then got in a vehicle and found that his handheld will not
work so well inside the metal of the car, as the car mobile station
does with its much better antenna.
Given time, some quite bizarre scenarios can occur resulting in
people having to carry several handsets around. and despite all
that, have to remain near to a transportable set to receive calls
intended for him in a supposedly fixed position. With SELCALL
it is possible to bring back some of the bad old problems with
phones and mobile phones.
The solution is for a person who is away from the radio which
is normally assigned to him, to defeat the SELCALL
system so that he can hear calls for him. This is done by pressing
a 'def' button on the radio or, via a menu, defeating the SELCALL
system. It also means that callers need both to SELCALL him and
give a spoken call so that he will hear the call if listening
by ear.
Another solution is for the sender, upon not receiving a response
from the called mobile, to then send the group call SELCALL.
A group call SELCALL means that the sender enters in a code which
is recognised by all of the mobiles in a certain group. Having
opened the speakers on all mobiles, the sender can then speak
out the callsign and name of the person required. When the person
answers, he can state the SELCALL of the radio he is using, and
the call can be set up again thus closing the other radios off
during the conversation.
A pager is a small and light radio receiver. It's size and weight
mean that it is far more convenient to carry personally than,
for example, a mobile phone or a two way radio. They are designed
for optimum battery life, so that they can
last about one month before the battery has to be changed. They
are usually powered by an ordinary disposable battery of the type
that can be purchased from nearly any general store. To add to
that, they are much cheaper to buy and about one fourth of the
cost to run than for example a mobile phone.
A typical use for them is for callout alert.
In some models, there is a loud tone when the
pager is called, in some there is the option of a vibration alert
so that the user will not be embarrassed if in a meeting or sound
sensitive area. In this case the user will have to have pre-arranged
the meaning of the alert, and either go to a pre-determined meeting
point or call a phone number. Some models of pager have more than
one paging sound in order that several different predetermined
messages can be sent.
More expensive models feature a small screen which may have either
numbers or letters and numbers on its screen. In that case, a
message can be left on the screen for the user to read later should
he not hear the beeper. The pager usually remembers the last 10
messages. The sender can now send a phone number to be dialled,
or a radio callsign to be called, or even leave a message (usually
of up to 255 characters) giving further details of the reason
for the alert.
These days pagers have become the backbone of many organisation's
callout plan, with most emergency services depending on pagers
to alert key staff quickly in the case of emergency. However there
are some disturbing aspects to paging that you have to be aware
of and have prepared for before you trust them totally. First
though, lets review how they work.
Pagers are radio devices usually working at frequencies around
160MHZ. The area of coverage of them will depend entirely on the
coverage of the radio base station network to which the user has
subscribed. If the user roams out of the area for which he has
paid a subscription, then the base stations in that area will
not be programmed to call the pager and the call will be lost.
If the radio waves become blocked to the user, for example if
the user goes underground or in a screened place in a building,
then the call will be lost. The problem is that if the alert did
not reach the user for any reason, the sender will not know this.
Pagers are usually one way devices and so the sender does not
know if the call succeeded or failed. If the user fails to respond,
the sender just has to keep paging and re-paging until the user
answers.
If the base station has been disabled
by a disaster, for example by having the mast knocked down by
a storm, then the signal will not be transmitted at all. Like
all radio base stations, Paging transmitters do not stand alone
but need two vital services from the ground, Power and Line. A
typical Pager station has enough battery back-up
for about 8-16 hours operation without mains power. A long power
outage will stop that station from working.
The paging stations have to know what pagers to call. To do this,
the paging station receives a so called 'Paging list'
from a control computer, usually situated very many miles away.
This paging list in turn must come to the station usually by telephone
line private wire. If the lines
are down to the station then the station will have no paging list
to send.
The sender has to alert the paging computer system by phoning
the office of the paging company and either speaking to an operator,
or typing the message from his phone pad. If the telephone system
is out of order, then you cannot call the paging centre.
For a small area of operation, say over a 10KM radius, a 'stand
alone' private paging system can be
installed. The coverage area of the system will now depend entirely
on the position of the antenna of the transmitter. These systems
are usually basic tone only systems but have the advantage that
they are independent of the local telecom net, have no running
costs apart from the initial cost of the equipment, and are usually
very quick to install. On the down side, You do need a radio licence
for such devices unless the government has allocated a special
general paging frequency for such private
systems.
Apart from the same vulnerability to disaster as other conventional
systems suffer, paging systems often only cover areas where there
are concentrations of business users, that is, not rural areas.
This is so because the profit margins on paging operations are
quite small, whereas the cost of a paging station may be just
as high as for any radio base station. There may be future systems
operating from satellites to offset this problem, when installed,
users would have global availability. However if the user cannot
call his office to ask for instructions, the usefulness of these
global pagers is much reduced, so in fact paging may be best used
in conjunction with another mobile communications system.
In the future it seems that paging will have competition from
the mobile phone sector. The latest
mobile phones are only slightly bigger and heavier than a pager,
and the user has to carry a phone anyway in order to reply to
the page. As the latest mobile phone systems are digital, there
is little complication in building in paging capability into the
phone itself. In the Short message service (SMS)
offered by the GSM (Global System for Mobilecommunications)
system for example, messages of under 255 characters are passed
over the call set up channels, so that the message charge is very
low.
The message is stored in the phone as numbers or text in much
the same way as a pager, including a helpful beep. The big advantage
is that the GSM system positively knows if the message was received
or not, and is able to notify the sender. It
is even possible for the user to reply to the sender to acknowledge
what action he will take. It seems that there are no complications
to adding such a service to the future satellite services, and
so they all plan to offer such a service.
In the future this will mean that the sender can call the message
centre over a satellite link, and have the paging message sent
down on a satellite link also, meaning immunity from ground disaster
at last!
Line Extenders, also called 'Radio in the local loop',', these
are a method of extending a telephone line
by radio. A station is set up in a town where there is working
telephone system, and a line is connected to the station. At the
other end, a telephone is connected to a special device, which
carries out the conversion of signals automatically. Versions
also exist enabling many mobiles to access the line, thus enabling
telephone service to be extended to them.
Line extenders are a mature and reliable product now, and they
are used all over the world to provide telephone service to areas
where the wiring does not penetrate. The equipment is compact
and fairly cheap. The problem is that it is only as good as the
local telephone exchange that you have connected to. If international
connections in the area are poor, you will have not gained much
over the other global methods, except perhaps cheapness. In a
disaster, the local phone system will be either destroyed or severely
overloaded, so it may be best not to trust only to this method.
Long term aid missions though can benefit from this arrangement
very cheaply.
Many users of the communications systems mentioned so far are
heartily fed up with what we have provided. They are very unhappy
with the fact that they almost always have to read a complex looking
manual and spend hours by trial and error before they can use
the system which their engineer is so satisfied with.
What seems so much like second nature to engineers is actually
hostile to users who feel that they are much too busy to fiddle
with such irrelevancies. We are living in a new era, the 'customer
is always right' attitude means that users are much less likely
to put up with us techno-people if we don't deliver what they
want.
Just about everyone can use a telephone. That is why the mobile
phone service is so popular. This is
a great technical achievement. Behind the scenes, millions of
dollars worth of computers and a huge network of base stations
are invisible to the user. That is why when asked what they would
really wish for, nearly all aid workers rock their head to one
side, sigh, and confess that they want a mobile phone.
The public mobile phone system, also known as the cellular phone
system is properly known as the Public Land Mobile Network (PLMN).
Mobile phone systems work in a way similar to the other systems
we have described. They need base stations to connect to. In the
case of a disaster, they are not likely to be working. This is
because few base stations have diesel generators, and usually
have battery backup for only 8 hours of service once the mains
goes off. Also, they rely on lines or microwave links going to
a parent computerised switching system called the Base Station
Controller (BSC) or Mobile Telephone Switching Office (MTSO).
If these lines are disrupted, or the BSC has failed, then you
are out of luck.
Even if the PLMN survives the disaster, one big problem is that
most base stations have capacity for less than only 30 calls
per cell. In a disaster, the working stations are sure to be busy
with calls from local people, and you may have to wait a long
time before there is a free channel at the base station to carry
your call. You also have the problem of finding someone to sell
you the mobile phones for the system in operation, and setting
up a valid subscription to the service. This
will be very hard as the local people will no doubt have beaten
you to it.
The operator of the system has a different perspective. When asked
"is your system still working", he will look at his
toll ticket tape, recording the money earned, and reply with a
smile of satisfaction that it is working very well indeed, thank
you. They rarely remember to mention that the control channels
that set up the calls are completely overloaded, and in fact users
are finding the system nearly useless because there is rarely
a free channel when anyone tries to call them, the call then fails.71
Other users in the cell may have bottomless pits of money at
their disposal, and so having seized a channel, they hold it sometimes
for days in order not to lose contact with their office. In fact,
most systems offer the capability for the operator to allow only
calls from 'emergency services' to get through. In practice this
is seldom switched on because of the loss of money this would
involve. This is a sensitive subject and one which operators are
often reluctant to discuss.
If the area has the Global System for Mobilecommunications (GSM)
operational in the area, you are in a much better position. GSM
phones are standard over the whole world, so you could bring GSM
phones from Britain, and use them in Beirut or Siagon without
a problem. If people in Britain phone you on your usual number,
the system will find you wherever in the world you are, and put
the call through even if the caller has no knowledge of where
you are. This is called International Roaming,
and is a great triumph of GSM.
Unfortunately there are still some snags. It may be that the operator
of the PLMN in the disaster area has not signed a Roaming
agreement with your operator at home, in
which case roaming will not be possible. A bigger problem is that
the GSM system is not by any means universal, so there are many
places where incompatible systems are in use, so your phone can't
be used. Also, in may countries, mobile service is provided only
in cities, leaving no service at all once outside well populated
areas.
Several manufacturers make quick fit emergency mobile phone systems.
They consist of a kind of advanced base station, and special mobile
phones for use with them. The problem is that they usually only
offer connection within the area that the base station covers.
Sometimes an outside line connection is available by satellite
connection by dialling a number but usually not. The big problem
is that to do this they require several duplex frequencies, one
for each simultaneous call plus one for the control frequencies.
You could not use it unless the government authority in the area
agrees. This could take quite some time. In addition, it is much
more expensive than the conventional systems just described but
not any more effective, so you would need to justify the cost.
Another solution is the DECT system, a self organising mobile
communications system rather like a mini mobile phone network.
This has been described in ch 6.2.1.
At first, position finding may seem to be an unnecessary complication
to an already expensive and complex operation. but consider for
a moment the kind of problems faced by field staff. In the first
phase, a 'rec' team will have to assess the needs
of the prospective clients. Often, the team are driving in a place
where they have never been before, and often without the aid of
road signs because they have been destroyed by the disaster, are
in an unreadable script, or have never been provided. Even a map
is useless unless you know your present position. Upon reaching
the scene of the greatest need, they will now have to find the
name of the place that they have found, but again, will they be
able to do that, or unambiguously pronounce the name of the place?
Having compiled their report and moved on, the main supply vehicles
must now find the same place, so that the 'clients' identified
by the 'rec' team can be helped without delay. Finding and then
re-finding places becomes so difficult that many operations leave
this job of distribution to local militias or other 'helpful'
persons. The result is often that the supplies end up in the hands
of 'sergeant Bilko' types and find their
way into the black market economy rather
than to the needy victims. Clearly, delivering the supplies that
you have paid for to the users that you have intended is much
better.
Safety is another factor. Should your field staff
get into trouble and urgently need help, the rescue teams
cannot help unless they accurately know the position of the distressed
field team. This is why, at sea, the very first thing a ship must
send over the radio during a mayday call, is
its position. If the radio then fails, the rescue ships at least
know where to go to find out what is wrong.
These then are among the many reasons why a humanitarian aid field
unit may want quite accurate position fixing. Until about 1995,
such devices were much to expensive and impractical for use by
such small NGO's with small budgets, but by 1995 all that has
changed. By that time, hand-held battery powered units with all
the desired capabilities were about USD 300-500, which is about
the same size weight and cost as one handheld radio. The dominant
system is use at the time of writing, at the end of 1996 is the
Global Positioning System (GPS).
By the turn of the century it is expected that most of the new
LEOsat satellite phone systems will offer position
fixing as a standard part of the service
and so very soon position fixing will become an indispensable
part of the many new products and services. For the moment though,
let us look at some of the ways of using GPS.
GPS was developed for position fixing at sea in the air, and for
the positioning of missiles. The GPS receiver on the ground finds
its range to two or more satellites that could be in view of him.
A computer inside the GPS unit computes its position based on
the range to those satellites and the position of the satellites
at the time the ranges were made. For the satellites to know their
position, they have to have accurate clock, so a further bonus
of GPS is very accurate time.
At sea or in the air a latitude and longitude position
is very useful. There are few other relative landmarks
to reference to anyway. On the ground however we want to find
our way along a road network to reach a certain town or village,
so for the position information to be any use at all, we would
need to have maps with the lat and long grid printed
over them. I have to tell you now that most useful road maps do
not offer this, whereas most useful lat and long maps are not
much good at showing ground detail and in any case cannot be purchased
at an airport petrol station.
The alternative is to use 'relative positioning'.
Suppose that you arrive at a city in the disaster zone, and are
given a road map, that you purchased at the airport petrol station,
to find your way to the next rendezvous. What you would do is
go to a place on the map which is very distinct. Go there (or
send someone there) and Using the GPS, find the exact position
of this place. It will now become a WAYPOINT. Record
this waypoint in your book and agree with other members of your
organisation the name of this waypoint and its absolute (lat and
long) position. You will have to do this because other teams
may have a different map with a different scale, colour code scheme,
icon scheme and grid system to the one you are using.
Your map will hopefully have a reasonable scale printed on the
border, and an indication of which way is north, though this is
usually (but not always) the direction pointing straight up. Now
mark the position of the place you want to go next. This will
be another waypoint, you can name it what you like but the place
name on the map is best (provided you can read and pronounce it!).
Using a ruler and divider, you can draw a line between the two
places and measure the line. You now know the direction and range
of the other waypoint. You can now type this information into
your GPS, and it will remember the location of the two waypoints,
and even calculate the absolute lat and long of the other waypoint
for you.
Well, that was jolly good schoolboy fun, but why did we do that?
As you drive down the rutted roads in the bad weather for hours,
you will probably wonder where you are and if you are going in
the right direction at all. Your GPS will probably be battery
powered, so rather than leave it on all the
time you should switch it on only when you need position information.
You would then switch on your GPS, and ask it what is the range
and direction, from where you are now, to any of the waypoints
you have entered into its memory. You will get a readout saying,
"270 degrees 7Km". Now you can pinpoint yourself on
the rather sparse map you have, even without any grid marks
on the map and even if there is no landmark at that point. Furthermore,
if you have a compass, you can use the direction for steering,
provided the road system is simple enough. However you must be
clear if the baring shown on the GPS screen, is the baring FROM
the waypoint or TO it (or you could be driving the wrong way..
it has happened).
When you arrive at the scene of some obvious need, you can ask
GPS for the position, and create a new waypoint at this spot.
You can then use the relative information about how far away from
another known waypoint this is, to draw its position accurately
on you map. You can also use the absolute lat and long position
to send to the other teams by radio, so that they can mark it
in on their maps and find their way more easily. They will also
know if they have got the right spot.
Used wisely, GPS can give a great deal of time and money saving
help, and all at very modest outlay. GPS will probably be in service
for many years to come and so you can invest without fear of the
equipment becoming obsolete very soon. However it is important
to remember to ask for a model that can calculate waypoints and
give relative positions, or GPS will be useless without lat and
Long maps, which you can bet will not be available to you. You
should also share waypoint information with other teams, and collect
positions from them. This not only saves misunderstanding, but
adds a significant safety factor, you never know when they will
fail to report and you will have to find them without being able
to communicate with them. You should likewise report to someone
else what waypoints you are expecting to be visiting before your
next communication.
There are other systems than GPS for position finding, some based
on ground based transmitter stations, such as Decca,
Omega and Loran. However these are vulnerable
to the user straying out of the range of the system, and to the
failure of the ground based radio base stations providing the
signals. The advantage of spaced bases systems such as GPS, Transit
and Glonass, is that they are immune from land based
disasters, and have global coverage.
In the future we could have advanced satellite systems offering
global mobile phone systems at a very
reasonable cost. When that happens, then the users will at last
have what they think they really need. It is also thought that
there will be a kind of satellite version of packet radio,
giving access to Internet. A world wide library
system called World Wide Web will make it
possible to for example fetch maps and photographs of a place
together with a detailed guidebook about it instantly on your
screen. You will be able to read this book on your screen as it
too will be on the WWW (it is hoped).
However this will not make your investment in the conventional
systems obsolete because the future systems may be just as prone
to overloading as the present ones are. Therefore you should consider
them to be your secondary system until they mature, well into
the first decade of the 21st century. It is an exciting future
for the communications industry, but also a confusing one, that
is why DRCF is here to help you. Future revisions of
Disaster Communications will include anything promising
that comes up. To do this we need your help, both financially
and with information.
There is also excitement on the legal front. Remember all the
legal hurdles to getting even a simple system set up? Well in
1996 there will be an International Convention on Emergency Telecommunications,
which, it is hoped, will clarify and simplify the situation. The
aim is to make moving equipment across borders easier and setting
up emergency communications systems rapid and efficient by bringing
in new legislation. It is hoped that many countries will sign
up for an agreement to allow a waiver of the usual red tape in
the case of an acute emergency, but of course there will be many
terms and conditions to be met by prospective foreign rescue teams.
The DRCF will be here explain them.
Everyone realises the need for better training of key staff in
the arts of Emergency Telecommunications. Not just techno- waffle
for the boffins, but down to earth clear grounding for the decision
makers in our business.
Many of the decision makers in aid and disaster work are intelligent,
experienced and highly motivated people. Few however have any
kind of telecommunications background and this often results in
the application of technology which is sometimes less than appropriate.
These are busy people who need courses that will fill their needs
for keeping up to date with todays can-do technology but keeping
the language at popular level.
The DRCF and several other groups are actively working
on establishing a framework for defining target groups for training
and developing such courses. It is hoped to be able to offer theoretical
and practical courses covering all aspects of this work, from
a co-operative and co-ordinated base, within a time scale of about
two years.
This book will be updated and expanded as experts submit more
input to it. In addition it is proposed to add smaller booklets
about topics which attract popular attention.
We have a lot to do before the International Decade for Natural
Disaster Reduction (IDNDR)
is out!
66In fact they go to the trouble of arranging 'talk through' systems on their duplex base stations to give this effect.
67See Appendix for the full International Phonetic Alphabet.
68The antennas for Liverpool Coastguard's Marine Rescue Centre at Bootle are on top of Blackpool Tower, giving a commanding coverage of the Irish Sea.
69The UNDHA portable repeater for use at a disaster site has enough self contained battery power for 24hrs sustained operation.
70A personal opinion, your experts may advise otherwise.
71During the Koybe earthquake disaster, the mobile phone system survived in tact. The operators claim that service was provided without overload throughout the rescue period- Ericsson.