Chapter 6. HOW TO INSTALL A RADIO SYSTEM

Topics:

6.1	Where to put the equipment
6.1.1	The Radio Room
6.1.1.1	Radio Desk
6.1.1.2	Power supply
6.2	Installation
6.2.1	Transceiver
6.2.1.1	Cooling
6.2.1.2	Microphone clip
6.2.2	Power Supplies
6.2.2.1	Connections
6.2.2.2	Colour Coding
6.2.2.3	Plugs and sockets
6.2.2.4	Solar Panel
6.2.2.5	Battery
6.2.2.6	Fail to battery
6.2.3	Protection against lightening
6.2.3.1	Arrestors
6.2.3.2	Aerials
6.2.3.3	Transceiver
6.2.3.4	Static
6.2.4	Aerials
6.2.4.1	Aerial Supports
6.2.4.2	Aerial adjustment
6.2.4.3	Erection
6.2.4.4	In the Radio Room
6.2.4.5	Fitting a plug to a coaxial cable
6.2.4.6	SWR measurement and aerial tuning
6.3	Final Checks
6.3.1	Power
6.3.2	Netting
6.3.3	Operating
6.3.4	Look around
6.4	Mobile Installations
6.4.1	Transceiver
6.4.2	Power supply
6.4.3	Aerial

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Once you have obtained the radio equipment there will be an instinctive urgency to get it installed and working as soon as possible. However long term benefits should not normally be sacrificed for rapid results! The equipment should be installed by the most competent person available, see para. 5.1.4. for options regarding technician.

If you are using a technician unfamiliar with the various locations make sure you have as much information as possible about each site available for him to study before he visits them, when possible give him the opportunity of discussing a site with someone who is familiar with it. You should make sure you have all the necessary equipment ready for him to take with him and if equipment such as aerial poles need to be got locally you should advise those in charge at each location regarding the size of poles and that they are to have them ready for his arrival. Wherever possible unsuitable temporary arrangements, e.g. wiring, should not be fitted because once the transceiver is working this may never be changed. For example the limitation in performance caused by the loss of voltage in a long thin wire being used as a power lead from battery to transceiver may never be discovered. The resulting poor quality of transmissions may well become accepted as normal for that particular location whereas with more careful and proper installation things could be much improved.

You should allow adequate time for the installation by building in an allowance for delays which you, from experience, have learnt to expect. Bearing in mind the culture and traditions of the area you are in, for example, a long welcoming session before you can proceed with the work. If the equipment arrives at your HQ direct from the manufacturers in large packages it will need re-packing in suitable sizes for transporting by small aircraft, Land Rover or canoe to the various installation sites. You must ensure that any new packing is sufficiently shock-absorbent and waterproof.

Whether or not the equipment needs re-packing you should take every opportunity to check that all the items are actually there and if possible that they are working before despatching it to the various sites. Although everything is new and apparently working it is wiser for the installer to have spare parts with him to avoid delays and abortive journeys if a fault occurs during transporting or installing the equipment. Another point to consider is whether you may need documentation for the equipment you or your technician will be carrying. The need for this will vary from country to country. When you travel by air within Zaire, for instance, you have to pass through immigration and sometimes customs and you may need to prove to the authorities concerned that you are authorised to carry this equipment and that customs etc. have already been paid when it originally entered the country. So make sure that all the necessary papers are available including customs receipts, radio licences and written authority from your organisation saying who you are, where you are going and what equipment you are carrying. It is better to be prepared than to risk confiscation of the equipment.

6.1. Where to put the equipment

Ideally your technician should have sufficient time at each location to supervise each step of the installation and this ought to include time for inspection of the site and time for deciding the details of where best to locate the equipment. However in practise he may have only a short time to spend on each site or you may have no technician available and so you may need to do these things yourself. Therefore before you start any installation work look around your location and ask yourself where is the best place to put it all? Ideally you should select or build a room to house the radio equipment then clear a large area of ground of trees and any other obstructions then erect aerial poles of the required height. The solar panel would be mounted in an unshaded position and the battery would be adjacent to the transceiver. However in practice the ideal is rarely achieved. Indeed you may have little choice in locating your equipment in an existing building complex and it may not be acceptable to clear fruit trees such as mangoes which are a valuable source of food for the people. The aim should be to locate the transceiver within 25 metres of the aerial and as close as possible to the battery. It is important to locate the battery near to the radio because of the high current e.g. a peak of 20 amps, flowing in the connecting cable. However the solar panel can be further from the battery as the solar charging current may be only 1 or 2 amps.

6.1.1. The Radio Room

Try to find a permanent place for the transceiver and its battery. This place will have to be secure and you may have to fit burglar bars and reliable locks. It is not a good idea to have to carry the transceiver and/or its battery from its place of use during the day to a safe storage place at night. This practice could well result in unnecessary damage being done to the equipment because of constant moving and careless handling as well as causing inconvenience to those responsible for using and moving the equipment. In one situation where only one lady was available to carry a vented battery, her tee-shirts were spoiled from acid burns which could easily have resulted in hurt to the person. There was also the problem of keeping the transceiver dry whilst carrying it through wind and heavy rain to keep a scheduled radio contact. Conversation by radio is not private in as much that anyone with a suitable receiver can listen on your frequency. You may however wish to fit the equipment in a separate room which affords some form of privacy to the operator and prevents conversations being overheard. If this is desirable but not possible then the operator can wear earphones so preventing the distant end of the conversation being overheard. Rooms in which other people are working and talking, also rooms which echo should be avoided because the sounds in the room will be picked up by the microphone and transmitted as background noise. This will not help the person receiving your transmission as they may already be listening through the crackle of static and interfering transmissions. Any form of sound absorbing screens or the "telephone hoods" as used in airports can be of help. Provision must be made for keeping the equipment dry even if this means covering it and its desk with a plastic sheet. Tropical rain can penetrate roofs, windows and doors!

6.1.1.1 Radio Desk

You should consider the ergonomics of operating the equipment and so prevent any time-wasting exercise. The transceiver should be located on a table or desk of a suitable height for the operator to sit at and where there is sufficient light for reading and writing messages. There should also be adequate space for writing and for using a desk microphone. If this is to be a busy station it is helpful to provide the operator with a foot operated switch in place of the hand operated "press to talk" switch. In Zaire desks have been made specifically to house the radio equipment. These were made of solid hard wood and with a good padlock were safe and secure. The desk was designed so that it was impossible to close it without first disconnecting aerial and power leads thus reminding the operator of the vital necessity of this action. You must not make holes in the desk for these cables to go through, see Fig. 6.1. If an aerial selector switch is used it should be within easy reach of the operator not on a distant wall. If several aerials are used with an aerial selector switch, this switch can be fitted on the outside of the desk so that only the single cable from the switch to the transceiver needs to be disconnected. The fold-back lid of the desk can be used to display information e.g. lists of stations with their call-signs and times of operation, also the phonetic alphabet. The layout of the desk in Fig.6.1 provides for ease of operating and hence reduces operator time. The desk microphone and foot switch give the operator two hands free for writing and refering to any documents.

6.1.1.2 Power supply

Your power supply connections whether from a battery or mains should be a permament and reliable installation from the beginning, not a temporary and unsafe mix of wires and sockets as so often has happened.
MAINS. A mains supply will come from a socket on the wall or perhaps a socket hanging from a cable on a wall. You should firmly fix a socket near the transceiver because long mains cables on the floor or draped round tables and chairs are a danger to people and equipment. If your transceiver has provision for an earth connection on its power lead make sure that the earth pin on the wall socket you are using is connected and actually goes to an earth point.

BATTERY. The battery should be located as near as possible to the transceiver. Experience has shown that the only battery in a village that is not flat is often the radio battery. Disastrous results have occurred from disconnecting the battery, taking it to a vehicle, flattening it trying to start the engine and then reconnecting it to the transceiver with the wrong polarity. Therefore the battery should be in a secure enclosure close to the transceiver. One method is to screw the wooden case in which the battery was transported to the floor, then put the battery in and secure wooden bars across the top to hold it in. If it is a vented battery there must be room between the bars for making visual inspection of the acid level and for easy topping up with distilled water.

Where for reasons of security it is impossible to keep the battery permanently in the radio room then you should install a permanently fixed cable from the battery to the radio room rather than be constantly carrying it back and forwards. If this cable is to go between buildings then for safety reasons it should go underground. The voltage drop in this cable should be as low as possible and never more than one volt and this will in fact limit the distance you can have between battery and transceiver. For guidance on this note that the thicker the metal conductor inside the cable the less will be the voltage loss. Also the lower the current flowing in a cable the less will be the voltage loss. For example a conductor with a cross-sectional area of 3.25 sq. mm. will drop one volt over a length of 15 metres when the current is 10 amps or over a length of 60 metres when the current is 2.5 amps. So if your transceiver uses 10 amps on transmit your battery must not be more than 15 metres away. The best solution is to try to have both transceiver and battery located securely in the same room.

PEDAL GENERATOR. A pedal generator is not very noisy and if located in a room shared with other people it will not cause any more interference than a radio operator speaking into a microphone or the sound from a loudspeaker. The generator can have the transceiver mounted on it so that one person sits on it to both pedal and operate or it can be located adjacent to the transceiver's position so that one person pedals while another does the operating. Experience has shown that if one person pedals while a second transmits then the speech transmitted is much clearer and more understandable. The generator should be in a room which is as cool and has as much ventilation as possible.

6.2. Installation

A good initial installation will require much more work than a quick job of just putting the equipment on a table and erecting an aerial. But the resultant good reliability and hence availability of communications has shown that sufficient time spent on installation to be a cost-effective exercise. There can be a conflict of demands for funds in an organisation if each department is trying to keep its expenditure to a minimum. For example one department may have been responsible for funding the purchase of the equipment, another for the installation and a further for the operating. If there is no one person with technical understanding and financial responsibility for the overall project then inefficiency can result. In one radio handbook it is written " the efficiency of communications and the long term reliability of the transceivers are critically dependent upon correct installation and the use of a suitable aerial." Your equipment should have with it both operating and installation instructions, when ordering the transceiver you should have specified a technical manual see para. 5.1.1. Always read and take note of all instructions and try to follow them but you may find that in your particular circumstances this may be a little difficult. One of the aims of this book is to help you solve problems you will not find mentioned in your technical manual.

6.2.1. Transceiver

Ideally the first step in your installation should be to fit the transceiver into its chosen position as this will determine the length and routing of the connecting cables. When you have the transceiver set up with its power source ready and working then you should begin to get the aerial up because you will need the transceiver working to tune the aerial and test its effectiveness. However there are times when you may have to do it differently. For instance, if the time your radio technician can stay at a certain location is very limited it may be a good idea to get the aerial up beforehand as this can be a time-consuming exercise, always depending of course that the aerial can be sent on in advance and that there is someone at the location capable of following correctly the instructions you would need to send for erecting it. It is best to have your technician or some other competent person there to supervise all the details of the installation and this is what you should aim for. So now we will look at points concerning the installation of the transceiver.

6.2.1.1. Cooling

For security reasons the transceiver may be housed in an enclosed space e.g. the radio desk. In mains operated transceivers the regulator transistors can produce a lot of heat and require a fan to keep them cool. You should obtain the quietest fan possible e.g. axial flow type, and fix it on a sound absorbing mount if necessary. To ensure a flow of air around the transceiver it is an advantage to mount it on two pieces of wood about 2 inches square with holes drilled in the wood for any "feet" on the transceiver and the wood attached to the desk see Fig. 6.2.

6.2.1.2 Microphone clip

A hand-held or fist microphone is supplied with a clip for holding the microphone when it is not in use. The clips are intended to be fitted in a place convenient for resting the microphone e.g. dashboard of a car or the side of a desk. No provision in the form of holes, screws etc. is usually made for these clips to go on the transceiver but in practice they frequently end up attached to it. One clip was found attached by a single existing screw so that it had swivelled round and broken an indicator light on the front of the transceiver. Another example is of two holes drilled into the side of the transceiver case and self-tapping screws being used to secure the clip. Whilst this provided a firm fitting for the clip the screws protruded inside and made it very difficult to remove the case. More seriously if the screws had been put in a different place they could well have made contact with the components inside the transceiver thus causing damage to the circuits they were touching. So some thought should be given to the where and how of the apparently simple exercise of fitting a clip. When the transceiver has to be carried about it is an advantage to have the microphone clip on it because it means you do not have the microphone swinging around on the end of its cable but otherwise this should not be necessary. If you do need to fix it on the case first all remove the case from the transceiver and ensure that the screws will not touch any internal parts and that it will not make it difficult to fit the case back on. Note also the stiffness of the spring in these clips vary with the result that it is almost impossible to put some microphones in and out while it has difficulty retaining others. The spring usually takes the form of a piece of metal the angle of which can be bent to give the required tension.

6.2.2. Power Supplies

Your power supply is a most vital link in your equipment e.g. with no mains and a flat battery your transceiver is useless! So it is well worth while taking time and trouble to get it right at the beginning. Experience has shown that seemingly small things like misunderstanding the colour coding of a cable for instance can have quite an effect on vital equipment. A power supply depends both on its source of power and on its connecting cables for it to work well.

6.2.2.1. Connections

The power and aerial connections are usually found on the rear of the transceiver. These should be made as accessible as possible for disconnecting the cables or you can fit another plug and socket in the cables in a more convenient place. Transceivers have been and still are suffering severe and costly damage because incorrect power connections are made. Some have been destroyed because 230 volts AC mains have been connected to models designed to operate on 12 volt DC only. Some of the things you will need to check are as follows:

1. Are there internal connections or switches which change the transceiver to work from 12 volt DC, 110 volt or 220 volt AC? You should be able to make the appropriate connections by carefully following your manufacturers instructions. Some models may have switches on the rear of the transceiver which require adjustment by a screwdriver.

2. Are there two power leads provided which plug into the same power socket on the transceiver? One will be for 12 volt DC and when plugged into the transceiver will be connected to the 12 volt DC input pins in the socket. The other will be for your AC mains volts and when plugged in will be connected to the AC input pins.

For AC mains operation check that the transceiver is set to operate at the required voltage e.g. 110, 220 or 240 volts and fit a suitable mains plug i.e. of the type normally used in your area. This will avoid any confusion in the future. For DC operation there will be a positive and a negative wire which should be terminated in different connectors which are not interchangeable and which can be easily identified as positive or negative. If you are not using such connectors and have to remove the insulation from the wires to attach them to the battery terminal make sure that they are clearly labelled as positive and negative. A common fault in 12 volt DC supplies is the wrong polarity connection being made but transceivers can be safeguarded as explained in para.5.2.5.1.

6.2.2.2. Colour Coding

One reason for mistakes being made is due to the colour coding of the cables because no world-wide standard exists. As a result the colours of the cables in your equipment will depend on what each individual manufacturer decides or on what is demanded in the country of manufacture. Some combinations of cable colours which have been seen in use are listed below.

This lack of standardisation has lead to mistakes being made. An example of this was when a person making a connection on a 12 volt transceiver which had black as negative and white as positive was himself familiar with the AC mains system which has black as line and white as neutral with the result that he mistakenly assumed that on this transceiver black was positive and white was negative. If different coloured wire is going to be used for the same voltage connections then the cables should be labelled to show what voltage and polarity they carry and a wiring diagram should be provided. However in practice labels can come off and diagrams be lost especially if there are changes in staff. One can always tie a knot in the positive cable to identify it. It is recommended that you decide on a colour code for your wiring which will be used for all the equipment in your network, for example the traditional colours in UK for DC wiring was red for positive and black for negative. These should be used throughout the wiring from solar panel and regulator to the battery and the transceiver. Where necessary you should change the existing cable. Whilst this will involve additional cost it could well be repaid in saving future catastrophes such as the inability of a different person to reconnect any wires which have become disconnected.

6.2.2.3. Plugs and sockets

Plugs and sockets which will only fit together in one orientation will have a locating lug and key-way to ensure a correct fit. If the plugs are often pulled out e.g. for the power supply, it is worth painting matching halves of the plug and socket in the same colour, but one that contrasts with the rest of the radio. This will assist the person to fit the plug correctly and should reduce attempts at forcing the plug in the wrong way.

6.2.2.4. Solar Panel

POSITION.

In Equatorial regions the solar panel can be mounted nearly horizontal. Rain will clean the surface of the panel but there must be sufficient slope for it to run off. e.g. 15 degrees from the horizontal. Panels installed north of the equator should slope towards the south, those south of it should slope northwards. An approximate guide is to make the angle of slope equal to the number of degrees of latitude of the geographical location. The panel should have an uninterrupted view of the sun especially from 9 a.m. to 3 p.m.

FIXING.

When a panel is mounted on a metal roof note the following;

(a) it should be spaced at least 2 inches off the roof on pieces of wood to allow for cooling.

(b) the metal roof should be electrically connected to earth.

(c) the panel should be mounted below the highest point of the roof unless it is protected by lightening arrestors.

Solar panels have been installed on thatched roofs, this presents no problems provided the panels are mounted on a wooden frame which rests on the thatch. Wires can then be easily passed through the roof and secured inside either to the existing roof frame or to extra lengths of wood attached below the roof frame. In fact panels can be mounted on any suitable structure e.g. a wooden frame at ground level if this can be safe and secure. The extent to which it is mechanically screwed to its mounting will be determined by both the local type of storms and to the probability of it being stolen. Always use rust-proofed screws, do not use nails to secure the panel.

DIODES.

A blocking diode may have been fitted to the solar panel during manufacture, see para. 3.2.5.1. to para. 3.2.5.5. for description of various diodes. It is recommended that the blocking diode be removed or if this is not practical then shorted out and one should be fitted instead near the battery. The reason for this is that these diodes have been destroyed by lightening and so needed replacing. It is so much easier to test and replace a diode in the radio room than when lying on your back on a hot tin roof trying to work on connections underneath a solar panel. The diode connections should be made to rigid points e.g. soldered lugs rather than just connected to flexible cables as the movement of such cables could break the diode leads.

REGULATORS.

Where a solar regulator is used it may have a blocking diode within it. If the regulator is the "dump" type see para.3.2.6. you should mount the resistors so that they have a free circulation of air because they become very hot and should not be touched.

6.2.2.5. Battery

TRAVEL.

New batteries are available "dry-charged" i.e. there is no acid in the battery but it is partly charged. If you are travelling by air you may not be permitted to take a battery filled with acid so either a "dry-charged" one or a sealed one would be necessary. Do not forget to have sufficient battery acid available to fill the "dry-charged" one when you reach your location. The acid required will have a S G in the region of 1.240. Note that the battery will get very hot when it is filled with acid and the metal connections may be too hot to hold.

SECURITY.

Where there is need to prevent misuse of the battery as mentioned in para. 6.1.1.2. you can further safeguard it by sawing off the battery lugs along the dotted line in Fig, 6.3. Spade terminations of the type used on vehicles can then be attached by self-tapping screws or soldered to the lug. If available use a wider spade for the positive than for the negative. You can also paint the positive red and negative black or blue and scratch + and - on the battery as a further means of identifying polarity. If a vented battery is used and it is not housed in a wooden crate then stand it on a solid piece of wood larger than its base or in a plastic tray. This will prevent on overflow of acid from reaching the floor.

CONNECTIONS.

The cables connected to the battery should be via proper battery connectors. Crocodile or other types of clips are not suitable for permament use. Not only do they make poor electrical connection, especially as their teeth wear away, but they also wear away the battery lugs so preventing future use of proper connectors. The position of the positive and negative lugs are not the same on all batteries. Usually the lugs are both on one side of the battery so that if you turn the battery round the position of the positive and negative terminals are reversed. So if it has had to be moved do not automatically assume that the positive is still on your right ,for instance, as it was before, but always carefully check that you are reconnecting to the correct lug. When you install the power leads for the battery make them sufficiently long for connection to a different size and shape of battery for sooner or later you will need to replace it. Whatever method of connection is used on the battery all the metal parts must be covered with a good layer of an anti-corrosion grease.

6.2.2.6. Fail to battery

At least one make of transceiver has a 6 pin input power socket which accepts a cable and plug either from the AC mains or from a 12 volt battery. However the mains plug serves a second purpose by completing another electrical circuit because two of its pins are shorted. Therefore if you are installing your own "fail to battery" relay and circuit first check in detail what is connected to each pin of the transceiver power socket. A simple "fail to battery" circuit was described in para.3.2.1.2.

6.2.3. Protection against lightening

Another point to consider before commencing installation which many people are not aware of is lightening protection. When broadcast receivers first came into use in the early days of radio they used a long piece of wire for an aerial. This aerial had always to be disconnected from the receiver during storms to protect it from lightening strikes. So most people who used radios were aware of the problem. Today people are used to having portable transistor sets which have their aerials built in to the set so that the question of disconnecting aerials during thunderstorms never arises. When it comes to short wave transceivers the users must be made aware of the damage that can be caused by lightening and must be instructed in the necessary precautions. This is particularly important in countries such as Zaire where thunder and lightening are very frequent occurrences. For instance Kenya has a National Lightening Protection Committee which arranges the installation of lightening arrestors within that country. Where there is no such official advice and help available it is absolutely necessary to alert the radio communications users to the possible dangers and how to cope with them. Lightening can cause the failure of costly transistors and other components within a transceiver and can even destroy it altogether. It can also cause injury to the operator who attempts to use it during thunder or even to someone who happens to be by a radio at the moment of a lightening strike. The lightening reaches your transceiver by way of the aerial cable and in some cases by the power supply cable. We will now look at some of the ways lightening protection can be provided.

6.2.3.1. Arrestors

If you are not familiar with lightening arrestors take a look at the highest point of any building in your area. You may see lightening arrestors with several spikes pointing upwards and connected to earth by a thick metal conductor. The expectation is that lightening will take the easiest path to earth via the arrestor thus safeguarding the building etc. on which it is mounted. Arrestors can be mounted near to but higher than solar panels to give them protection. The conductor to earth should be capable of carrying 50 amps. A good earth can be made by burying a 6 foot water pipe or metal rod and keeping the ground damp.

6.2.3.2. Aerials

There are several methods of stopping lightening passing through the aerial and reaching the transceiver. The safest method and the most simple which has not been known to fail is to always disconnect the transceiver from the aerial after it has been used and never to use it during a thunderstorm. You must ensure that the radio operator has been given these instructions and understands their importance. Also these instructions should be displayed in a prominent position and in as many languages as may be necessary so that if someone other than the normal operator is using the transceiver they will know what to do. After disconnecting the aerial it can either be connected to earth or just left "floating" i.e. not connected to anything, but it should not be left within 30 cms. of the transceiver. Other methods of protection include gas discharge lightening arrestors which can be screwed into the coaxial cable between the aerial and its transceiver.

6.2.3.3. Transceiver

A limited form of protection is often found in transceivers in the form of "back to back " diodes connected across the receiver input. Both normal rectifying diodes and zener diodes have been used in this role. Transceivers powered from solar charged batteries should be disconnected from the battery when not in use because lightening striking the solar panel could be conducted to the battery and hence to the transceiver.

6.2.3.4. Static

Users of transceivers in dry desert areas across Africa have complained of getting an electrical shock when they touch the aerial or the transceiver to which the aerial is connected. The reason was because of a build up of static electricity on the aerial. In such situations it is necessary to have an aerial switch or other arrangement which earths the aerial either all the time that the transceiver is not in use or at least just before the aerial is connected to the transceiver to discharge the static. Its case should also be earthed to avoid the build-up of static.

6.2.4 Aerials

An aerial properly installed can stay up and operate correctly for many years. Therefore it is worth allowing sufficient time, for example several hours, for aerial erection. Attempts at forward planning are not always successful in some cultures. The sending of messages to one village to cut two straight 12 metre poles from the forest and have them ready for a certain day resulted in no poles being available that day! However , as soon as the technician arrived in the village the men departed to the forest, returning with the necessary poles four hours later. Whenever it is possible a competent person should install the aerial. Whilst it is time consuming for a technician to spend days away from his workshop, it is nevertheless a worthwhile exercise. There are many examples of incorrectly installed aerials. For example, in Zaire an aerial has been found erected at 90 degrees to the required direction and one where the coaxial cable was tied to the top of one of the poles while the one end of the aerial was almost on the ground! In Tanzania an aerial was supplied of the correct length but during installation pieces of the aerial had been cut off to make it fit between two posts.

6.2.4.1 Aerial Supports

Survey the site and decide the best location for the aerial and what sort of support you are going to use e.g. existing buildings and trees or poles.

1. Anchor points on buildings. Make sure that they are strong and secure enough to hold the weight of the aerial. Facia boards are not normally satisfactory. If metal hooks are fitted to wooden beams be aware of the fact that some woods rot rapidly in the tropics. Ensure that the aerial or its associated wire or rope will not rub against adjacent walls or overhanging roofs whilst swinging about in strong winds.

2. Trees. Palm trees can frequently be found in convenient positions to support aerials but the fronds need to be kept cut so that they do not foul the aerial. It should be allowed to hang a little slack because of the movement of the palm tree in storms could break a tight aerial. The same considerations apply to other trees used as supports. Fix the aerial to a rigid part of the tree, not on thin branches which wave about in storms.

3. Metal masts. Where no suitably located buildings or trees are available then aerial masts can be erected. Masts can be made from metal tubing e.g. galvanised steel, aluminium etc. depending on what is available. They will require guy wires about every 4 metres, depending on the strength of the pole material used. At least 3 guy wires are necessary at each point to give all round support. Barbed wire has been successfully used for aerial guys. If it is thought that the aerial will remain in the same place for many years then the mast and the anchor points for the guy wires can be set in concrete.

4. Wooden poles. In Zaire 12 metre wooden poles set into 2 metre holes in the ground have been used as aerial supports. Although the poles were painted with used engine oil some rotted after 3 to 5 years and had to be replaced. If set firmly into the ground these should be self-supporting and not need guys.

5. Movable bases. A mission in Zaire has found that they have had to relocate aerials because the radio room has had to be changed to different buildings. Hence they are trying out a movable aerial base made from pieces of steel e.g. two 1 metre steel bars in a cross and also old vehicle wheel hubs as anchor points for guys. These bases are all buried several feet underground but can be dug up when necessary.

6. Guidelines. The following should be aimed for but may not be achieved. Do not put the aerial parallel to electric power lines or other long pieces of metal wire. Do not suspend the aerial above a tin roof. Have some 20 metres of clear ground in front of the aerial, that is in the direction the power in it is to be transmitted. A horizontal dipole can be supported at each end. If thick co-axial cable is used then an extra pole can be used to support the centre of the aerial. Do not let either of the aerial wires touch this pole, it should be attached to the central insulator. A central support is necessary for inverted-vee aerials, see Fig. 2.5.

6.2.4.2. Aerial adjustment

The aerial will have been cut either to the correct length or if you have so specified to some 10 cms. too long to allow for tuning after erection. Ideally it should be possible to raise and lower the aerial by means of halyards of nylon rope and pulleys. One disadvantage of nylon rope was that after several years of exposure to the sun in equatorial Africa the rope broke easily. Also in some places a rope halyard is an attractive item and could well be stolen. Hard-drawn wire has been used instead as it is more durable and less noticeable than white rope. An alternative is to use an aerial clamp of the type shown in Fig, 6.4. This was developed by apprentices in Britain to serve the special requirements of being able to raise and lower for initial tuning then to leave the aerial erected whilst being able to recover the ropes. The aerial can be pulled up and lowered by he rope loop A. When adjustments are complete the aerial is pulled up and the eyelet will automatically be above the hole in the base. The rope loop B is now pulled down causing the metal rod to come down through the eyelet and to lock into the hole in the base. The ropes A and B are no longer needed and the knots in them can be untied enabling both of them to be pulled down to earth.

6.2.4.3. Erection

Do not attempt to erect an aerial if lightening can be seen or thunder heard. The length of the aerial together with its required direction and height will be determined from Chapter 2. Now comes the task of putting these theoretical ideals into practice. If the aerial is not going to be lowered for tuning then it should be the calculated theoretical length before erection. See para.2.2.1.

Having decided how and where the aerial will be erected uncoil it and its coaxial cable ensuring that there are no twists or kinks in it. If possible lay it out on the ground below where it is to be raised. This will confirm that the aerial supports are sufficiently far apart. Measure the length of each piece of aerial wire as a final confirmation that the aerial length is correct. These checks are necessary as shown by the following experience. While looking at two dipole aerials which had been in use for some years in Zaire one did not "look right ". Its SWR was checked and found to be 4 which was much too high. It was lowered to the ground and measured. One wire was the correct length of 12.3 metres but the other wire was 10.1 metres which happened to be the correct length of the two wires on the other aerial. A possible explanation is that there was a mix up of wires during manufacture of the two aerials.

Check the length of coaxial cable on the aerial although you know how long it should be, 25 to 30 metres are typical lengths fitted by manufacturers unless you specify a special length. Also ensure that the coaxial cable is secured to the centre insulator and not left to hang only from its coaxial plug. Wire or nylon rope can be used between the aerial insulators and the tree, pole or building on which it is suspended. See Fig. 2.1. If wire is used check that it does not touch the aerial wire. Also do not use pieces of wire whose lengths are the same as or within 1 metre of the length of any one piece of aerial wire or any multiple of aerial wire length. For example, a dipole for 7.305 Mhz will comprise two pieces of wire each 9.76 metres long. Therefore the supporting wire should not be between 8.76 to 10,76 metres, 18.52 to 20.52 metres etc.This is because such wires can be resonant parasitic elements and can have a detrimental effect on the aerial.

Having taken these necessary precautions and having securely fastened the aerial insulators to their supporting wire or rope you are ready to raise it into position. Note that your supporting wire or rope at this stage should be considerably longer than the amount you will finally need otherwise you will be unable to lift it into position especially if someone has to climb up a tree or ladder to fix it. The excess should not be cut until it is firmly and finally attached to its support. First raise and secure one end firmly to its point of suspension whilst taking care to remove any twists or kinks in wire and cable. If a pole is to be used to support the centre insulator, then erect this next, checking the aerial wires do not touch anything. Then the other end of the aerial can be raised and secured by its wire or rope to its support being careful all the time not to twist or make kinks in the wires and removing any that appear.

For aerials supported between solid buildings or rigid metal poles pull the supporting wire or rope until the aerial is reasonably straight. For aerials supported by trees let the aerial sag in the middle by up to 1 metre. If an aerial is 20 metres long and allowed to sag by 1 metre this will only permit an outward movement of 5 cms in both trees before the aerial is horizontal and tight. However it can be argued that the wind will be blowing both the trees in the same direction hence reducing any strain on the aerial. If thin wooden poles are used without guy ropes it is wiser to allow a little sag as a too tight aerial could cause the poles to break in a strong wind. Once the aerial is in position the coaxial cable can be routed to the radio room. The cable can be afforded some form of protection against damage by suspending it on poles some 3 or 4 metres above the ground. Do not use thin wire to attach the coaxial to the poles as this will cut into the cable. Either put some solid material between the wire and the cable or use cord or other broader material that has not any sharp edges.

6.2.4.4. In the Radio Room

When routing the coaxial cable to the radio room ensure that it does not rub on any rough surface or sharp edge e.g. the edge of a tin roof. Do not put too much pressure on the cable when making a bend rather let it be in a gentle curve. If there are several metres of aerial cable spare when it reaches the transceiver do not cut off the cable as it may be required if the radio is moved in the future. Do not coil up the excess cable but try to lay it out straight, in the roof space for example. Where the installation involves more than one coaxial cable label each one immediately you bring it into the room to avoid future confusion. SRoute the cables to the radio desk and then either to the aerial switch or to the transceiver. Aerial switch positions should be numbered e.g. 1 to 4. and the aerials connected so that they correspond with the channel number which they serve on the transceiver i.e. Aerial position 3 serves Channel 3.

6.2.4.5. Fitting a plug to a coaxial cable

The cable from your aerial will normally be a coaxial cable of which there are 2 common sizes. A thick one which is approximately 10 mm diameter and includes types RG 8/U, RG 213/U and URM 67. A thin one which is approximately 5 mm diameter and includes types RG 58/U and URM 43. The plug in common use is a PL-259, an additional adapter being required for fitting thin cable. If you have never soldered a plug to coaxial cable before it is recommended that you practice preparing the cable end using an extra piece of cable. Do not actually solder the plug on the practice cable. Step by step instructions for large size coaxial cable i.e. 10mm. Refer to Fig. 6.5.

1. Cut the coaxial cable (coax) to the required length.
2. Unscrew the coupling ring from the plug and put it onto the coax with the threaded end nearest to the cut end of the cable. Note. The coupling ring must be put on the cable first as it cannot be fitted after the plug has been soldered to the cable.
3. Remove 28 mm. of the outer sheath which is likely to be made of black plastic. This can be done by cutting round the sheath with a knife.
4. Using a small tip soldering iron and small diameter solder, apply solder to the braid from the point where the sheath finishes for some 15 mm along the braid.
5. Now cut the soldered braid , but not the inner insulation, with a fine saw or small tube or pipe cutter at 11 mm from the end of the sheath.
6. At a point 2 mm. from the cut in the braid now cut through the inner insulator but not the central conductor. Remove the cut piece.
7. Check that the coupling ring is still on the cable as instructed in step 2.
8. The cable is ready for fitting the plug. Gently screw the plug on to the cable ensuring that all the central conductor is inside the hollow central pin of the plug. Continue to screw the plug on to the cable, the thread on the plug will grip the black outer sheath and then the soldered braid should be seen through the solder holes of the plug.
9. With a small soldering iron with a small bit apply solder in the holes and solder the braid to the plug. Be careful not to overheat the cable in the plug.
10. Solder the central conductor where it protudes from the central pin. Now cut off any wire protuding from the pin and remove any excess solder.
11. Screw the coupling ring on to the plug and check that the assembled plug will screw into a socket.
12. If the far end of the cable is disconnected i.e. not yet connected to an aerial balun or a transceiver etc. then electrical tests can be performed on the cable.
13. If practical check there is contact, i.e. a resistance of only a few ohms, between the central pin of the plug and the distant centre of the coax. Also between the outer coupling ring and the braid at the distant end of the cable.
14. Provided there is nothing connected to the distant end of the coax check that there is a high resistance between the inner and outer connections to the cable. A resistance of 1M ohms or more can be expected. Note that if you are touching both the inner and outer conductors or both the metal parts of the meter probes, then you will be measuring your body resistance which could be only 200K ohms.

Fitting a plug to thin coaxial cable i.e. 5mm. e.g. RG-58A/V or URM43 or URM76. You will require the same plug PL-259 but also an adapter (Type UG-175/V) or reducer to enable the smaller diameter cable to be secured into the plug. Step by step instructions. Refer to Fig. 6.6.

1. Cut the coaxial cable (coax) to the required length.
2. Push the cable through the centre of the adapter such that the narrow end of the adapter is nearest to the cable.
3. Unscrew the coupling ring from the plug and put it onto the coax with the threaded end nearest to the cut end of the cable. Note. The coupling ring must be put on the cable first as it cannot be fitted after the plug has been soldered to the cable.
4. Remove 18 mm. of the outer sheath which is likely to be made of black plastic. This can be done by cutting round the sheath with a knife.
5. Ensure that the end of the adapter is level with the outer sheath.
6. Now cut the outer braid, but not the inner insulation, with a pair of small scissors at 10 mm from the end sheath. Remove the cut braid and fold the remaining braid back over the adapter. If necessary further trim the braid so that there is only 10mm folded over the adapter and it does not reach the tread.
7. At a point 2 mm. from the braid now cut through the inner insulator but not the central conductor. Remove the cut piece of insulation.
8. Apply solder to the central conductor.
9. Check that the coupling ring is still on the cable as instructed in step 3. and ensure that the braid is folded back over the adapter.
10. The cable is ready for fitting the plug. Gently screw the plug on to the adapter ensuring that all the central conductor is inside the hollow central pin of the plug. Continue to screw the plug on to the adapter, then the braid should be seen through the solder holes of the plug.
11. With a small soldering iron with a small bit apply solder in the holes and solder the braid to the plug. Be careful not to overheat the cable in the plug.
12. Solder the central conductor where it protudes from the central pin. Now cut off any wire protuding from the pin and remove any excess solder.
13. Screw the coupling ring on to the plug and check that the assembled plug will screw into a socket.
14. If the far end of the cable is disconnected i.e. not yet connected to an aerial balun or a transceiver etc. then electrical tests can be performed on the cable.
15. If practical check there is contact, i.e. a resistance of only a few ohms, between the central pin of the plug and the distant centre of the coax cable. Also between the outer coupling ring and the braid at the distant end of the cable.
16. Check that there is a high resistance between the inner and outer connections to the cable. A resistance of 1M ohms or more can be expected. Note that if you are touching both the inner and outer conductors or both the metal parts of the meter probes, then you will be measuring your body resistance which could be only 200K ohms.

6.2.4.6. SWR measurement and aerial tuning

The meaning of SWR has been explained in para 2.1 To measure SWR first familiarise yourself with the particular SWR meter by reading the instructions. However in many instances these are not available having been lost or mislaid. Examples of such instructions are: For single meter units there will be a switch labelled REF/VSWR or SET/READ or similar. Put the switch in REF or SET position and connect the meter between the transmitter and the aerial taking note of the labels on the sockets of the meter e.g. "Transmit" and "Antenna". With the transmitter giving a continuous output adjust the meter's variable control for the meter pointer to be at the REF or SET level on the dial. Methods of obtaining a continuous output can be obtained from the transmitter by:

(a) connecting a 2 tone oscillator into microphone socket
(b) unbalance the carrier null control.
(c) whistle or sing a continuous steady note into the microphone.

Now switch to VSWR or READ and note the meter reading which is the SWR. For two meter units: One meter reads power output to the aerial and the other the SWR. A variable control will need to be adjusted so that the power meter needle reads either full scale or at the SET position. The other meter now indicates the SWR. SPrecaution : never disconnect the aerial from the SWR meter when the radio is transmitting. The higher the SWR the less effective is the aerial. An indication of the percentage of power wasted i.e. reflected back from the aerial is given in Table 6.1.

Table 6.1.

The SWR can be measured once the aerial has been erected. For aerials that are difficult to take down and alter their length a SWR of 1.5 or less is acceptable and the aerial can remain as erected. For aerials that can be taken down easily the SWR should be adjusted to the minimum possible. To tune a dipole aerial first note its reading when erected e.g. 1.8. Lower the aerial and reduce the length of BOTH pieces of aerial wire by 3 cms. Do not cut the wire but twist it around the wire as shown in Fig. 6.7. Re-erect the aerial and measure its SWR, this could be for example 1.5. If at one stage the SWR rises after you have shortened the aerial increase the length again using some of the extra wire you have twisted around the aerial. Do not cut off the extra wire until the aerial tuning is complete.

6.3. Final Checks

All the preparations and the good installation should be rewarded by a good radio contact when you test the completed system. Arrangements should be made for a test contact at a specific time so that someone is listening specially for you but a final series of checks should be performed before the test transmission.

6.3.1. Power

1. Connect an ammeter in series with the solar battery charger. Record the value of charging current noting whether bright sunshine or dull and also the battery voltage.
2. Record the battery voltage with the transceiver:
   (a) switched off (b) on receive. (c) transmitting with a whistle
   or singing a continuous and steady note into the microphone. These measured voltages will depend on many factors, you could expect the voltage to fall by up to 0.5 volts when transceiver is switched on and by a further 1 volt during continuous transmission.
3. Connect a SWR meter in the aerial circuit next to the transmitter. Set the meter calibration control so that it reads power output at the particular frequency of transmission. Transmit by using a 2 tone Test Generator or by making a continuous loud note into the microphone. The meter should indicate a power output some 40 to 60 watts for a 100 to 150 watt pep transceiver providing the SWR is below 1.5. Higher SWR will result in a lower power output. Measure and record the SWR and power output for each channel with the transceiver connected to its appropriate aerial.

6.3.2. Netting

You will have specified the frequency of each channel in your transceivers when you ordered them. However the crystals in each set, although made to the same frequency, can differ by several hundreds of cycles. This difference sometimes can be heard when listening to a network of several stations. With the clarifier control set to give clear speech from one station when the next station speaks it can be necessary to adjust the clarifier and to readjust it when the original station is on again. This problem can be overcome by adjusting the frequency of all the transceivers to exactly the same frequency, a process called
NETTING

Ideally this will have been done already if:

• you have an accurate frequency counter i.e. one which reads to 1 or 10 cycles, and have set the crystal trimmer to give the exact frequency.
• you have brought the transceiver from your HQ station where you have netted the crystal to the frequency of that station.

If it has come direct from the manufacturer or has been used on another network, then check that it is netted onto your HQ station. The method of netting of each different make should be explained in the technical manual of the transceiver and some manufacturers e.g. AEL, make provision for this to be done in the field after the transceiver has been installed. You must consider how and when you are going to net your transceiver before leaving for your installation visit. However, if you do not have the technical knowledge or ability to net the transceivers it is not a major problem but simply means that all the stations will have to make greater use of their clarifier controls. As the crystals age so their frequencies change hence further netting can be performed. In an ideal situation this would be done after 3 months and 6 months and then annually. In reality many networks function without this being done.

6.3.3. Operating

Remove all your test equipment and go through the procedure of switching-on connecting any cables as described in the instructions. Let the operator perform all the operations and make a radio contact with another station at a prearranged contact time. At the same time you may check the operators method of sending and receiving and recording messages. Then let the operator switch off and disconnect any cables necessary. This sounds like an organised and controlled exercise however it can become chaotic as has been our experience of installing transceivers in remote African villages where these are to be controlled and operated by local people. You may have many interested villagers surrounding the building and blocking the light through the windows. For them to hear the voice of a known person hundreds of miles away causes great excitement and everyone in any position of authority wants to speak. So it is a good idea to try to instruct the operator in advance of the initial formal contact in as quiet a situation as possible.

6.3.4. Look around

Take a final look around and check to see if all is well with the equipment and that nothing has been moved or disturbed by all who had crowded into the room to see it working. Check that the cables on the outside have not be disturbed as well. Collect up all your tools and test equipment and make any final notes regarding the particular installation, especially the non-standard features as these are important for your central records and for future maintenance plans. Make sure that operating instructions and all other necessary information is left with the operator or person in charge in a secure and available position. Make sure they know how to top up the acid level in the battery and how long they can use the radio for each day whilst keeping the battery fully charged. After completing the installation of a system with a solar-powered supply designed for the needs of that particular station one usually gets asked questions such as: "Can we run a light off the radio battery in the evenings?" or "Can we charge another battery off the solar panel?" The answer must normally be "No, because then you will not have sufficient power for your radio and your equipment may be damaged by careless and incorrect connecting and disconnecting of the battery". Many faults have arisen from incorrect connections and radio batterys have been flattened and their lives shortened by extra or unauthorised loads. Impress on all concerned that the reliability of their radio link depends very much on how they use it and how they take care of their power source. Expatriate personnel are often very guilty of mis-use of batterys provided for radio use only. Where the radio battery may be the only fully charged one around there is a great temptation to use it for personal reasons but it must be understood that this must not happen.

6.4. Mobile Installations

Many HF SSB transceivers with power outputs up to 150 watts PEP are designed so that they can be used equally as well in vehicles or as a base station. Care must be taken in the mobile installation so as to make best use of this facility.

6.4.1. Transceiver

The mobile transceiver should come with its manufacturers special mobile mount. A common place to put it is below the dashboard in front of the passengers seat. This is a good location in as much as it provides some shading of the transceiver from direct sunlight and it can be operated by the passenger. Enough legroom should be left for the passenger if long duration journeys are undertaken. The mounting should allow the transceiver to be easily fitted and removed by authorised persons but some form of lock may be necessary for security reasons. A fist or hand microphone must be used and a clip for securing it fitted on or near the transceiver.

6.4.2. Power supply

A 150 watt pep transceiver operating from a 13.6 volts vehicle supply requires an average current of some 12 amps with a peak demand of 18 amps. Because of this relatively high current demand the transceivers power cable must be connected to the vehicles electrical system at a point where sufficient current is available. The current for the transceiver must not flow through any of the existing fuses because the fuse rating will only be sufficient for its present circuit. The cigarette lighter socket is not suitable for high powered sets though it could be used for 4 watts CB sets. The above constraints demand that the power cable for the transceiver must start from the vehicle battery and that you should install a 20 amp fuse in the cable. The nuts on the battery lugs on many vehicles were found to be worn round hence a grip rather than a spanner was necessary to release the nut. Also lugs were found loose on battery terminals as the terminals had worn thin hence some packing was necessary to ensure a reliable contact to the battery.

6.4.3. Aerial

You may have observed many vehicle aerials mounted on or near the rear "bumper" or "fender". This is not a good position because of the proximity of the vehicle body effects both the tuning of the aerial and the horizontal directions in which power is transmitted. Whilst mounting on a front wing is an improvement the centre of the roof is the most suitable location. The aerial will require tuning after installation Follow any instructions which you have concerning the tuning up of your particular aerial. For example a single frequency aerial can have a coil in the middle and a top section of stainless steel rod some 2 mm diameter. This aerial will have been designed so that 2 to 5 cms of the rod can slide into a housing and be locked by a screw. This enables the length of the aerial to be adjusted by several centimetres for tuning. If the rod is too long then cut off a centimetre at a time to achieve the lowest SWR. If you intend to use the vehicle for journeys with the complete aerial mounted then ensure that the aerial base is secure on a strong part of the vehicle body. The thin metal of a wing or a roof can become distorted by the force of the aerial when travelling so the body may need reinforcing. It is recommended that the aerial be completely removed from its base and carried inside the vehicle for journeys through the jungle. Otherwise overhanging foliage, bamboo etc. could soon damage it.