Chapter 8. HOW TO MAINTAIN A RADIO NETWORK

Topics:

8.1	Staff
8.2	Cost and Payment
8.3	Spare Parts
8.3.1	Fuses
8.4	Tools
8.4.1	Basic Tools
8.4.2	Workshop Tools
8.5	Routine Maintenence
8.6	Fault Finding
8.6.1	False Indications
8.6.1.1	Power Light
8.6.1.2	Transmit Light
8.6.2	Do It Yourself
8.6.2.1	Trial and Error
8.6.2.2	Diagnostic Aids
8.6.2.3	Testing Diodes
8.7	Workshop Repair
8.7.1	Requirements
8.7.2	Instructions
8.8	Contract Maintenence

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There are several aspects of a radio network which have to be satisfied if it is to give a continuous satisfactory service. These aspects are dealt with in each chapter, the importance of each has been stressed e.g. choice, installation and operating of the equipment. However you are unlikely to end up with a perfect system. There will be failures in the radio equipment, some of which may be due to design or manufacturing faults, others to poor installation or bad operating practices. Wherever possible the author analysed the faults which occurred in the radio systems in Zaire. This frequently showed that either the fault was not in the transceiver itself or if it was it had been caused by something external to the transceiver. The various ways to safeguard the transceivers and prevent some faults occurring are in the chapters of this book, for example see para. 5.2.5. After you have taken all reasonable precautions, there will still be the failures. It may be due to a fault within a semiconductor which is beyond your control or it may be due to somebody in a hurry forgetting to disconnect the aerial and thus allowing lightening to damage the transceiver.

Therefore you must make some provision for the maintenance of the whole network. Within a few hours of the author arriving in many towns and villages in Zaire the fact was known that a radio engineer had arrived and requests were made to look at transceivers that were not working. Enquiries revealed every time that no spare parts were kept, no manual or circuit diagrams were available and no provision had been made for maintenance. Hence the resulting situation of unserviceable transceivers which were unlikely to work until someone got round to taking them to a repair facility within the country or often in another country. A maintenance philosophy which relies on all faulty equipment being sent to a central workshop for repair and then being returned to their stations is not always appropriate for developing countries where there are very few such workshops and transport arrangements are difficult. If the equipment was not originally installed by a competent radio technician then when one becomes available he should make an inspection and upgrade as necessary all the installations.

8.1. Staff

There are often very few qualified full-time radio engineers or technicians working for missions and aid agencies in the developing countries of Central Africa. In July 1988 the author knew of no other radio technician working with any Protestant mission in the northern half of Zaire an area of about 500,000 square miles where there are many radio networks. The need for short-wave communications is decreasing in the developed countries as satellite systems take over therefore there are now not so many communication engineers available who have had experience with short-wave communication. So in countries where short-wave communications are important, nationals need to be trained in this aspect of radio engineering. This, however, is a long term solution. An interim solution could be for several co-operating organisations to provide a technician in turn, e.g. for 2 years who will service the equipment for all the organisations. Another person could also run a programme to train nationals as technicians. It will be necessary to be aware of the visa and work permit regulations of each particular country before you plan to send in expatriate personnel.

8.2. Cost and Payment

The maintenance facility may be allowed an annual sum of money to perform a service to an organisation or it may have to be self-supporting financially. The financial arrangements should be well defined and estimates of the various costs made at an early stage see para. 5.1.6. It should be decided who will pay for:

1. Repair of transceivers in the workshop including time and parts.
2. Travel and accommodation costs of a technician visiting a distant station.
3. Recurring replacements e.g. batterys.

Also how the payment will be made especially in countries where bank cheques are not in common use and where bank transfers of money can take a long time. In these circumstances money is usually physically moved around the country with the attendant hazards. Examples of costs in 1987 were $15 an hour for a missionary radio technicians time when working on equipment of other churches and missions. One commercial firm would send out a technician from Britain to work in Africa for the cost of his travel, accommodation plus o300 per day. The costs of either providing a radio maintenance facility for your own use or using someone elses facility are considerable and must not be underestimated.

8.3. Spare Parts

If you are providing your own maintenance facility or even if you have arranged for a visiting technician to repair your equipment you should hold a range of spare parts. Providing you hold a good stock of spares your transceiver can be repaired rapidly and returned to service. The cost of spare parts was mentioned in para. 5.1.1. It is recommended that the spares should be kept at the central maintenance facility rather than having a full set at each station. This reduces the capital cost, e.g. 1 spare item for every 10 transceivers rather than 1 item with each transceiver. Originally the author put some spares with each transceiver in Zaire, however over a period of several years many of these spares were lost. This mainly occurred when there were changes of staff and when staff were absent for long periods. There are sometimes advantages in having the spares with the transceiver, for example when you are able to call upon the services of a nearby radio technician. If there is no recommended list of spares from the manufacturers or you do not wish to use the list then a guide to the selection of spares is given in order of priority.

1. Plug-in circuit boards or modules.
2. Mechanical parts which are liable to wear out e.g. switches, press buttons, relays and variable resistors such as volume controls.
3. Hot filament devices e.g. thermionic valves and indicator lights, not LEDs.
4. Plugs and sockets which are unplugged daily, e.g. aerial and power connections.
5. High power transistors used in the transmitter.
6. Loudspeaker and microphone.
7. Non standard components which are special to the particular transceiver.
8. A selection of transistors, resistors and capacitors if possible chosen by the person responsible for maintenance.

Keep an up to date list of all the spare parts you hold. Where the parts have an identifying number always use this to aid the identification of the correct part. An additional completely spare transceiver can be worth keeping at the central workshop so that this can be used as an immediate replacement for a faulty transceiver. In real life it has been found best to await the arrival into the workshop of the faulty one before dispatching the replacement. Otherwise once the replacement transceiver has arrived at the distant station the need to send back the faulty one seems less urgent. Indeed the known existence of a spare serviceable transceiver in the workshop can present a problem in some cultures. When there is a long waiting list of places requiring radio equipment the head of the organisation may not fully appreciate the need to have a little used spare transceiver. However if it is pointed out that it will be necessary to purchase a new aerial, battery, solar charger, microphone etc. to go with the spare transceiver to make a complete station then the idea may not appear so attractive.

8.3.1. Fuses

Most modern radio equipment requires replacement fuses of the non-repairable type, that is where the fuse wire is enclosed in a glass or ceramic tube. On opening many fuse holders it has been found hat the fuse has blown and a piece of wire had been twisted around the fuse to keep the equipment going. The fusing value of the added wire was usually in excess of the fuse rating. Information on the fuse rating and fusing current of copper wire varies from different sources. In general one can say that a current which is twice the "fuse rating " will blow the fuse. If you have no proper fuses an indication of the size of wire to use instead is given in Table 8.1.

Table 8.1. Fuse Rating of Copper Wire.

8.4 Tools

The decision of what tools to provide for the places which have a transceiver should be based on what you expect the people to do. It may be that you do not wish anyone to attempt to do anything to the transceiver if it fails. It has been proved necessary in some places to paint in white paint the instruction "Do not open" in three languages on the cover of the transceivers and to also seal the screws which secure the cover with white paint. This instruction applied to all personnel, expatriate as well as local. No tools were supplied to these places.

8.4.1. Basic Tools

Providing you are confidant that the provision of tools to the people will not cause damage to the equipment, that the tools will not be lost or broken through misuse and that the people are competent to use all the tools i.e. including the multimeter then the following list is recommended.

1. A selection of screwdrivers to fit the necessary screws of the particular installation only.
2. Spanners if necessary. The modification of battery terminals see para. 6.2.2.5. means spanners for battery lugs are unnecessary.
3. A multimeter to cover the voltages and current in use and to measure resistances from 0 to 10M. A digital meter with an accuracy of only 3 digits e.g. to read 12.6 volts, is suitable. An analogue meter i.e. one with a pointer moving on a scale, should have suitable ranges. For example to measure a 12 volt solar supply system which may be between 10 to 18 volts, a meter scale of 0-20 volt DC will give a much more accurate reading than a scale of 0 to 50 volt DC. A 250 volt AC range is necessary for measuring mains voltage. Also check the manufacturers quoted accuracy for the meter which should be less than plus or minus 3%.
4. Where a multimeter is not supplied then a 230 volt mains bulb of 40 watts to 100 watts, fitted in a bulb-holder with two insulated cables, can be used carefully for checking the presence of mains voltage. Similarly for 12 volt systems a 12 volt car bulb can be used. If the bulb is to be used for testing a solar panel then the current consumption of the bulb should be less than half the current producing capacity of the solar panel e.g. a 12 volt 0.3 amp bulb to test a 12 volt 1 amp solar panel.
5. One or more of the following types of soldering irons should be made available.
   (a) Mains soldering iron to suit available voltage e.g. 110 volt or 230 volt. A small iron of about 20 watts for printed circuits and one of about 40 to 60 watts for coaxial cables.
   (b) 12 volt DC iron for use from either a vehicle or a radio battery are available at 30 watts.
   (c) Fire iron. These irons have no heating element and require heating by a flame e.g. charcoal fire or blow lamp.

8.4.2. Workshop Tools

The requirements for the workshop should be decided by the chief radio engineer of your organisation or this may be delegated to the technician who will be working in the shop. The choice of equipment should be made by a person who is knowledgeable about current electronic equipment and maintenance philosophy. The tools can consist of the basic ones mentioned in para.8.4.1. together with the more major items of para. 5.2.4. For transceivers which comprise mainly plug-in circuit boards a spare transceiver can save many items of test equipment.

8.5. Routine Maintenance

In the history of radio engineering there was an era when "preventative maintenance" was in vogue. A time was given for the expected service life of various components in the radio and these components were then changed well before they were expected to fail. Hence the radios were taken out of service for maintenance at arranged times and few unexpected breakdowns occurred. However this was an expensive method of maintenance and is now more usually found in areas of activity where the reliability and availability of equipment is important at any cost.

The situation likely to be found in a developing country is one in which it is often difficult to ensure that even the essential basic routine maintenance is performed. When questioning a driver if he had checked the oil level in the vehicle engine he said that it was alright because whenever the light flashed on the dashboard he put oil in the engine. The light was the oil pressure failure warning light!

In countries where the main object of the people is the need to survive and eat today, there is little thought for the needs of tomorrow so this attitude affects their ideas of maintenance. If the radio or the vehicle works today then all is well. If it does not work then it needs maintenance. An understanding of this attitude and the reason for it is necessary when instructing your staff about routine maintenance. The routine actions necessary should be included in the operating instructions given to all stations. An example of this is given in para. 7.2.2.7. and will depend to a large extent on the particular equipment at each station and on the capability of the operators. The most important points are listed below.

1. Check the acid level in a vented battery each week and refill with distilled or rain water.
2. Prevent the growth of corrosion on the battery terminals. Clean and cover with petroleum grease as necessary.
3. Clean the solar panel especially during any dry season when it should be checked every two weeks. In dry, dusty and desert areas it may be necessary to clean it more frequently.
4. Prevent the build-up of dust on the transceiver and microphone. Keep covered inside desk or with a dust cover when not in use.
5. Trees and vegetation grow rapidly in the tropics. Cut down branches before they have grown over or are touching the aerial and its cable. Stop creepers growing up aerial masts and cables.
6. If there is any means of measuring the state of charge of the battery e.g. voltage indicator or hydrometer, then record the state each day before using the transceiver. This record will give advance warning before a battery becomes too discharged due to (a) over use (b) under charging or (c) end of battery life.

8.6. Fault Finding

When a fault occurs some preliminary investigation should be made by the radio operator as discussed in para.7.2.3. Sometimes what the operator thinks is a possible fault can simply be that he has not followed operating instructions e.g. the RF Gain or Squelch control is in the wrong position. In any case the checks mentioned in para.7.2.3. should be done by the operator before contacting the maintenance person. Also the tests mentioned in para.8.6.2.1. could be done by the operator if the person responsible for maintenance considered this suitable. This can be done even if you have the option of calling in a radio technician and should be done before sending the transceiver off for repair. The amount of testing you want an operator to do should be specified when the equipment is installed and the relevant tools and written instructions left.

8.6.1. False Indications

Indicator lights are provided on transceivers to give confirmation that certain parts of the transceiver are working. Unless the indicators actual position in the circuit is known or its operation fully understood these lights can sometimes give a false indication.

8.6.1.1. Power Light

The DC power protection circuit of one make of 150 Watts PEP HF SSB transceiver is shown in Fig. 8.1. When the transceiver is connected to the 12 volt DC supply the 12 volts will go immediately to the power amplifier circuit via a 15 amp fuse. No voltage will be connected to the rest of the circuits until the transceiver is switched on when the Power light will be lit. If the 5 amp fuse blows this will be indicated by the Power light being out. However if only the 15 amp fuse blows the Power light will remain on so giving a false indication that the power is being supplied to all parts of the transceiver. Once the situation is understood the presence of 12 volts on the power amplifier can be verified by speaking into the microphone thus causing the Transmit light to flash provided the rest of the transmitter is working.

8.6.1.2. Transmit Light

This light indicates that RF voltage is present. The point at which the light is connected to the circuit depends on the particular design, see Fig. 8.3. If the light is connected to Point A it only means that transmitter power i.e., RF voltage, is available at that point. A fault in the filter could prevent any power reaching the aerial. A light connected to Point B simply shows that power is available at the RF filter output but it may have to pass through an aerial change-over relay before it reaches the transceiver output socket. Even if the power is reaching the output socket the aerial could be disconnected or have a fault and the Transmit light would still flash. Therefore you should be aware of the difference between what the light is labelled and what the lights actually indicate.

8.6.2. Do It Yourself

In such areas as house repair and car maintenance the idea of "Do it Yourself " (DIY) has become very popular in recent years. Various guide books and aids have been produced to help the "man in the street" do the job that was previously done by a skilled craftsman. Some jobs have turned into disasters whilst others have been successful often depending upon the aptitude and ability of the person doing the work and the standard of the DIY instructions. There exists a shortage of skilled technicians in many developing countries and so DIY can have an important place. Much care must be taken when introducing DIY into the field of radio communications engineering and notice must be taken of the sayings such as "a little knowledge is a dangerous thing" and "it can do more harm than good". However providing the DIY instructions are sufficiently well defined and also rigidly adhered to then this method of maintenance can give useful results. Before reaching this stage of repair the operator should have performed the Fault Finding procedure given in the sections of 7.2.3.

8.6.2.1. Trial and Error

It is possible for a person with little or no technical knowledge to perform tests on the parts of a radio system and in some cases effect a repair. The following tests are examples and further tests could be devised to suit your particular system. It should be noted that the results of these tests are not always conclusive.

1. Symptom. Transmit light flashes but no stations heard although noise from the receiver.
Test: Where an aerial switch is in use remove the coax aerial cable from the switch and connect it direct to the radio.
Result:

(a) Stations are now heard and normal contact is possible means a fault in either aerial switch or cable between switch and transceiver.
(b) no different then do next test.

2. Symptom: Noise from the transceiver loudspeaker but no stations are received on any channel.
Test: Disconnect the aerial. Turn RF Gain to maximum. Adjust AF Gain or Volume to give a reasonably loud noise (or hiss) from the loudspeaker. Touch the central pin only of the coax plug of the aerial cable to the centre of the transceivers aerial socket, being careful not to let the outer ring of the plug touch the transceiver.
Result:

(a) Noise from loudspeaker increases and possibly some stations heard. This means the receiver is working.
(b) Noise from loudspeaker remains the same.

3. Symptom: No noise from loudspeaker at maximum volume.
Test: Reduce volume control from maximum and plug in earphones.
Result:

(a) no noise in earphones when volume at maximum means a fault in the transceiver, probably in audio amplifier circuit.
(b) noise in earphones means either a failure of the loudspeaker or the circuit to it which may be via contacts in the earphone socket.

4. Symptom: The transmit light is on all the time that the transmit button is pressed although nobody is speaking into the microphone.
Test: Unplug the microphone from the transceiver and connect together the "press to transmit" contacts in the microphone socket.
Result:

(a) no difference. Fault in transceiver e.g. gain of microphone amplifier too high, amplifier oscillating or carrier balance needs adjusting.
(b) light is out means either wire open circuit on microphone or gain was too high in microphone amplifier.

There are disadvantages in this method of "trial and error" replacement. For example if there was a fault on the main part of the transceiver which had in turn caused the fault on the module then the replacement module would suffer the same fault. Therefore this method of repair should only be used when no better system is available.

8.6.2.2. Diagnostic Aids

One method used to test transceivers is to have a purpose designed test unit with a keyboard which is plugged into the transceiver. This unit then performs certain tests and measurements on the transceiver semi-automatically and displays the results on a screen. Such units have not been encountered amongst the missions and aid agencies in Central Africa.

A simplified and manual version of such test facilities exists in the form of three diagnostic boards designed by the author for the AEL 3030 transceiver which is produced by AEL Communications of Gatwick, UK. Whilst these particular boards can be only used in this model of transceiver, the principles of testing and indeed the circuits are suitable for other makes of transceivers, especially those from Trans World Communications Inc of the USA. The diagnostic boards are fitted, only one at a time, into the place of existing boards in the transceiver. An example of the tests which Test Board 101 can perform on the AEL 3030 is given in the following instructions which accompany the board. The circuit of Test Board 101 is shown in Fig. 8.3. This board has a row of LED lights along its top edge, numbered 1 to 7.

Test Board 101.
Switch off transceiver. Remove any mains power lead. Remove printed circuit board PC 101 and plug Test Board 101 into the same socket. Ensure aerial and microphone are connected and mains if used. Switch on the transceiver.

OBSERVE LIGHT NUMBER	YOU OPERATE	CONDITION OF LIGHT	THIS INDICATES	YOUR ACTION
1.	Press	Light	Correct	No action.
	transmit	flashes
To	button
Test	and	Off	No input	Check connections to
the	speak		from	microphone. Repair as
micro-	into		microphone	necessary. Otherwise
phone.	microphone.			try spare microphone.
2.	Transceiver	Off	Correct	No action.
Tests	on
that	receive	On	Relay	Short in microphone
12v			locked	leads to transmit
is being			on	button. Repair or
switched			Transmit	use spare microphone
to the
Transmit	Press and	On	Correct	No action.
circuits	hold on
	transmit	Off	Relay not	Break in microphone
			operating.	leads to transmit
				button. Try spare
				microphone. If fault
				remains change relay.
3.	When	On	Correct	No action.
Tests	transceiver
the	is on	Off	No 12	If 12 volts present in
12volt	transmit		volts on	Tests 2 or 4 then fault
supply	and also on		PC 101.	in the transceiver.
	receive.
4.	Set on	On	Correct	No action
Tests	Receive
that		Off	Relay	Check for short in
12volts			locked on	transmit button. Try
is being			transmit	spare microphone.
switched				Change relay.
to the	Press and
Receive	hold on	On	Relay not	Break in wires to the
circuits	Transmit		operating.	transmit button.
				Change relay.
		Off	Correct.	No action.
5.	Rotate
Tests	Squelch	On	Correct.	No action.
if the	fully
Squelch	anti-	Off	Squelch	Replace Squelch
control	clockwise		control	control.
is worn.			worn.
	Rotate	Slowly	Correct.	No action.
	Squelch	goes
	slowly	off.
	clockwise.
		Goes	Squelch	Replace Squelch
		out	control	control.
		instantly.	worn.
6.	No
Tests	operations	On	Correct	No action.
Loud-
speaker.		Off	No circuit	Check connections
			through	to loud speaker
			loudspeaker.	and earphone socket.
7.	Rotate	On	Correct.	No action.
Tests	Audio
if	fully	Off	Audio	Replace audio
Audio	clockwise.		control is	control.
control			worn.
is	Rotate	Slowly	Correct	No action.
worn.	Audio	goes
	slowly	off.
	anti-
	clockwise	Goes out	Audio	Replace Audio
		instantly.	control	control.
			is worn.

8.6.2.3. Testing Diodes

Select the OHMS range on a multimeter and connect the diode between the leads. Measure its resistance and then reverse the leads and measure its resistance in the reverse direction. In one direction the resistance should be low e.g. 10 to 300 ohms, and in the other direction it should be high e.g. 1 Megohm = 1,000,000 ohms or more. If the diodes resistance is similar to these values then it is serviceable.

8.7. Workshop Repair

The aim of all users of radio communications equipment should be either for their own organisation to have a radio workshop, providing they have sufficient equipment to justify this, or to have definite arrangements with other workshops to repair the equipment. Workshop repairs is a subject on its own and no attempt is made to explain the methodology of repair. The cost of maintenance was mentioned in para.5.1.6. and of equipping a workshop in 5.2.4. The other aspects of staff, payments and spare parts have been mentioned in paras.8.1 to 8.3.

8.7.1. Requirements

To perform satisfactory repairs in a workshop it is necessary to have:

• A qualified and capable radio technician.
• Adequate test equipment, tools and working space.
• A reliable source of sufficient electrical power.
• A secure and dust free room with adequate lighting and ventilation.
• A store of sufficient spare components and parts.
• Technical manuals for each type or model of transceiver to be repaired.

8.7.2. Instructions

Radio operators should be instructed and encouraged to perform the test specified at their station before sending the equipment to the workshop. They should be instructed to send the microphone with the transceiver and any separate mains or other power unit used. Also the power cable and plug, aerial switch and its connecting cable if used. It must all be packed in a way suitable for the mode of transport.

8.8. Contract Maintenance

Contract maintenance should be considered where there exists a reliable commercial radio repair facility which will usually be in a large city e.g. as in Nairobi. Also where there exists means of transporting equipment to and from this facility at reasonably frequent intervals. The actual economics of each organisation will be different and you will need to compare all the advantages and disadvantages involved.

The questions and costs to ask of a proposed provider of contract maintenance include: Retaining fee, labour cost per hour, overheads involved in obtaining and handling spares, equipment transportation arrangements, technicians travel and accommodation, and the maximum time from reporting fault to completion of repairs if this is definable.