Topics:
| 5.1 | Costs |
| 5.1.1 | Capital Costs |
| 5.1.2 | Shipping |
| 5.1.3 | Customs Duty |
| 5.1.4 | Installation |
| 5.1.5 | Operating |
| 5.1.6 | Maintenance |
| 5.2 | Choice of equipment |
| 5.2.1 | Transceivers |
| 5.2.1.1 | Supply Voltage |
| 5.2.1.2 | Ease of maintenance and modification |
| 5.2.1.3 | Ease of use |
| 5.2.1.4 | Future availability |
| 5.2.1.5 | Protection |
| 5.2.1.6 | Channel Frequencies |
| 5.2.1.7 | Microphone |
| 5.2.1.8 | Power Requirements |
| 5.2.2 | Aerials |
| 5.2.3 | Power Sources |
| 5.2.4 | Test Equipment |
| 5.2.5 | Modifications |
| 5.2.5.1 | Reverse polarity protection |
| 5.2.5.2 | Microphone switches |
| 5.2.5.3 | Earphone socket |
| 5.2.5.4 | Squelch |
| 5.2.5.5 | Power light |
| 5.2.5.6 | Internal connections |
| 5.2.5.7 | Foot switch |
First impressions of the cost of a radio network can be deceptive. You may know that a basic transceiver can cost around £1,000 but before that transceiver and its associated equipment is installed and working the total cost can be up to £2,500. The cost of introducing a radio network can be divided into two parts. First there is the capital cost of the equipment together with the shipping, insurance, customs duty and installation which are "once only costs". Secondly there are the "recurring costs" of operating, maintaining and licensing the network.
5.1.1. Capital Costs
The £1,000 mentioned above is the cost of a basic transceiver. There are many additional items necessary as suggested in Table 5.1. which gives an indication of the approximate prices in 1988. Whilst not all the items listed will be necessary, you may require some of the additional facilities described in Chapter 9. The cost of the additions will need to be discovered at the time because they vary considerably with manufactures and time etc. An adequate selection of spare parts should be purchased with the transceivers. The manufacturers may have a recommended list of spares based on experience. Allow about 10% of the basic transceiver price for spares for each set you buy. Technical manuals of the transceivers must be obtained, preferably in the language of the country where they will be operated. The numbers of manuals will depend upon what provision you make for maintenance. If each station is responsible for maintaining their own sets then there should be a manual with each set. The purchase of major items of test equipment such as a signal generator or an oscilloscope will again depend upon your plans for maintenance, see para.5.2.4.
| Item. | Cost in £ |
| 150 watt pep SSB HF transceiver | 1,000 |
| Each additional Channel | 50 |
| Spare parts | 100 |
| AC power supply | 40 |
| USB and LSB | 80 |
| Hand-held (fist) microphone | 25 |
| Desk microphone | 80 |
| Earphones | 15 |
| Single dipole aerial | 150 |
| Broadband aerial | 300 |
| Aerial selector switch | 25 |
| Your specified modifications(para.5.2.5.) | 50 |
| Technical manuals | 10 |
| 12 volt battery | 80 |
| Solar battery charger | 250 |
| Mains battery charger | 50 |
The list may have to be extended to cover such items as petrol or diesel generator and aerial masts. The possibility of obtaining a discount price should be investigated especially if you are buying a large quantity of radios. Some manufacturers give concessionary prices to missions and aid groups, indeed some give gifts of equipment. Discounts of 10% to 40% have been obtained. Check if there is a tax on equipment when it is purchased e.g. Value Added Tax (VAT) in Great Britain, which need not be paid or can be reclaimed when you export the equipment. It is the resulting discounted price that must be considered e.g. a £1,000 radio with 40% discount costs £600, a £700 radio with 20% discount costs £560. You will have to make a list of your particular needs. If your set is mains operated and you wish it to switch automatically to battery operation when the mains fail, you will need a "fail to battery unit". If you employ a solar charger then you may not need a generator or a mains battery charger.
5.1.2. Shipping
To ship equipment from the country of manufacture to the country of use could take several days by air or several months by sea. Air freight costs more but the longer equipment is in transit the more likely is it to be damaged or lost so using the cheapest method is not always the most cost-effective in the end. It is usual for radio manufacturers to pack equipment in shock absorbent material in a cardboard box. You should instruct them or the shipping agency to further enclose the cardboard boxes in a strong wooden one. This is to give both added mechanical protection and to reduce the chances of cardboard boxes being opened and items stolen. Insurance may cover the cost of replacing any equipment stolen but the time and effort necessary to recover the cost, reorder and ship the replacements will mean a delay in the installation and availability of your radio network. Therefore any steps you take to prevent loss of equipment at any time is worthwhile. The following example gives some idea of the cost of shipping equipment by air freight from Britain to Zaire in 1986. You must, of course, make sure you have up-to-date information for your own estimates. It shows that there are other things beside the actual freight charges.
| £ | |
| To supply wooden box, pack band and mark | 35.00 |
| Delivery to the airport | 8.00 |
| Air freight charges on 147 kilos at £2.25 per kilo | 330.75 |
| Airway bill charges, documentation etc. | 20.00 |
| Insurance | 10.00 |
| Telex with flight details | 6.00 |
| Total | £409.75 |
If you have small amounts of equipment to come out the best and safest way is often for someone to bring it out with their personal luggage even if you have to pay excess baggage costs but you must make sure they have all the necessary documentation with them.
5.1.3. Customs Duty
The custom duty payable varies from country to country and can also depend on the type of organisation you are working with e.g. commercial, foreign government aid programme, church or mission. Some countries allow properly documented gifts of equipment going to non-profit making organisations to come in free of duty, others do not, while again others give this concession only to a few aid agencies. The regulations and duty payable can also be changed without much warning so make sure you get as much up-to-date information as you can. An example of what can happen is that the cost of equipment ordered in U.K. in 1986, as a gift to a church, was doubled by the imposition of customs duty just before its arrival a few months later. Previously all genuine gifts had come in free of duty for many years. In some cases customs duty is charged not only on the value of the equipment but on the total cost of equipment, freight charges and insurance. It is therefore important to obtain full details of all likely charges including any local tax and possible storage and handling costs. In some places it can be difficult to get accurate and reliable information thus making it hard to know whether or not the amount you are asked for is the true amount. If you are not familiar with the system it would be worthwhile using an agent who is known to be reliable by other missions or groups. You would have to pay for this service but it could save you time and money as an experienced importing agent would know what was legally required to be paid.
5.1.4 Installation
After you have imported the equipment into the country there will be further expenditure for transporting it, together with a technician to install it, to its final destination. The cost for this can vary depending on availability of transport and technician and the remoteness of the location. For instance, if there is no other way, it may be necessary to charter a small plane. The cost of a day's charter with Mission Aviation Fellowship (MAF) to a station one and a half hours flying time away was in 1988 in Zaire £300. A commercial charter company would charge double this. In practice however it is often possible to share costs with others or to make use of local transport. As regards the installation work it is very important to get things fixed up correctly. A properly installed station will function better and longer and be more cost effective, even if you have to pay a technician to do it, than one badly installed by someone who knows nothing about it. It is even worse still to use someone who thinks he knows what he is doing when he really does not. See chapter on Installation. There are several options open to you regarding using a technician:
Option 2. Use one of your personnel who has a practical aptitude and an appreciation of things electrical. If he reads and understands the information in this book and can follow instructions sensibly the installation should be successful.
Option 3. Obtain the services of a local technician either from another mission or group or from a local company if there is one. Costs may vary but could be £10 to £20 per hour.
Option 4. Use a technician employed by the manufacturer of the equipment. This is an expensive option as it could involve, for example, the cost of flying out the technician from U.K. and paying a daily rate of £300 for each day he is away from U.K. Therefore to get such a person to spend several days at a remote location in Africa could cost some £3,000.
5.1.5. Operating
Who will operate the radio? How long will they spend each day sending and receiving messages and getting answers to messages and passing on requests for help or information? At a small station the extra demand on people's time due to the introduction of the radio may be low so that it can be absorbed with no extra cost. At the HQ station of a large network it will be different. Here it may be necessary for someone to be available all day both to operate when required and to deal with messages. The question of employing and training a radio operator and the responsibility of who should pay his wages ought to be carefully thought out beforehand. There will also be a small cost involved in the provision of "log books" to keep a record of all messages both sent and received. This is usually a legal condition of your radio licence.
5.1.6. Maintenance
You should decide how you are going to maintain your network before you buy your equipment. There are many factors which will determine the annual maintenance costs and therefore this is a difficult figure to estimate.
The need for maintenance will be minimised by certain factors which include good quality control during manufacture, having safeguards built into equipment, by good design of installation at each station and by having good operating procedures. These are dealt with in detail in this book. If your network will have twenty five or more stations you should consider having your own radio technician and workshop unless you are in an area where good reliable repair facilities are available at reasonable cost from other sources. The initial cost of equipping a workshop with the basic test equipment can start at £1,000 depending on the technician's choice. See para. 5.2.4. for choice of test equipment. To this you may need to add the cost of providing a building and work benches and seats, lights and fans or an air conditioner.
Then there is the annual cost of employing the technician. This is one area of cost in which certainly church missions and to a lesser extent aid agencies have an advantage over commercial concerns. The annual allowance paid to an expatriate missionary radio technician working in an African country was about one quarter of that paid to a similarly qualified person by a commercial organisation. Once you have established a repair facility you will usually find that other groups will come to you requesting you to do repairs on their equipment. If your technician has time available to do this then this could be a source of income to help with your costs.
An alternative to setting up your own workshop may be to arrange for prompt and effective repair work through an existing organisation. Some individual groups have a reliable facility in their own area but a more widespread organisation is MAF who because it has to maintain the equipment in its aircraft have some workshops of their own and sometimes is able to offer repair facilities to others. In Zaire the Catholic church is spread over the whole country and has radios at some five hundred locations. It has its own organisation for the supply and repair of radios and also offers a repair service to other groups. The cost of using a repair service other than your own will consist of the transport costs of getting the equipment to and from the workshop, the cost of the technicians time e.g. £10 to £20 per hour and the cost of replacement parts.
After you have decided the plan for your radio network and obtained the necessary permission you will need to make your shopping list. If you have had to give details of your chosen transceivers in order to get your permission you should have already studied the next section!
5.2.1. Transceivers
There are many glossy brochures advertising radio communications equipment. Pictures show vehicles with aerials sweptback as they speed across the desert or through the forest and the equipment is claimed to be "highly reliable for all conditions". Such claims are meaningless unless data such as the "mean time between failure" (MTBF) is quoted for specific operating conditions and this data is normally not available. Organisations such as MAF make a study of transceivers suitable for use in countries in which they operate and may be able to advise you. You should aim for the simplest transceiver that will satisfy your needs. A leading manufacturer of transceivers recently introduced a new crystal controlled model by claiming: "You do not have to be a computer programmer to operate it or an electrical engineer to repair it!" There now follows a list of some of the things to look for when selecting a transceiver.
5.2.1.1. Supply Voltage
You should discover what voltages are actually available at the site where you intend to install a transceiver. For example you may be told that a 220 volt AC mains supply is available but in reality this could fall to 185 volts at certain times. The voltage requirement of a transceiver may be given as one fixed voltage e.g. 220 volts or it may be able to be set at any one of several voltages e.g. 210, 220, 230 or 240 volts. Enquire from the manufacturer the AC voltage range over which the transceiver will really operate as this may be greater than that quoted in the specification. One British transceiver was found that would operate satisfactorily when the main voltage had fallen to 190 volts. Battery voltage. There is generally a misunderstanding about the voltage required for a battery operated transceiver. You may find a transceiver which is said to operate from a 12 volt DC supply. However the specification for such equipment is usually based on an input voltage of 13.6 volts because this is the voltage of a vehicle battery on charge i.e. with vehicle engine running. When the transceiver is operated from a battery which is not on charge at the time then the voltage supply may well be just 12 volts and the specification may be different. For example a transceiver which produces 150 watt PEP with a 13.6 volt supply may only produce 100 watt PEP at 12 volts. Be aware of the real voltage which will be available and ensure that you obtain a transceiver that will operate satisfactorily from that voltage.
5.2.1.2. Ease of maintenance and modification
Can the transceiver be easily dismantled for servicing? There are some, e.g. the TWC ones from U.S.A. and AEL from the U.K., which have plug-in circuit boards. This means that the components are built onto a board which can be simply unplugged from the chassis of the set and an identical replacement board can be plugged in, should a component on the circuit board fail. With such a system it is often possible for someone with little radio knowledge to locate and correct a fault by simply taking out and replacing each board in turn with a new board. It is then easier to send a single faulty board to be repaired at your nearest radio workshop than to send the whole transceiver. Please read para.8.6.2. on maintaining your network for further details of this procedure. Can the transceiver be easily modified e.g. to add an additional frequency? In the case of Traeger (Australia) this was done by adding a single circuit board whereas some radios will require several components to be soldered into various parts of the transceiver. Ensure that the Technical Manual for each set contains full circuit diagrams and testing procedures with numerical values. If you require more detailed information ask for this as part of the purchase arrangement, otherwise additional information may be more difficult to obtain at a later date.
5.2.1.3. Ease of use
An explanation of controls etc. was given in para 3.1.3. You do not want the front of the transceiver covered with controls and indicators that the operator may never use. The minimum controls necessary for a SSB transceiver are: ON/OFF, VOLUME, CLARIFIER and a CHANNEL SELECTOR if more than one channel is fitted. A SQUELCH control and a TRANSMIT indicator will also usually be found. The use of earphones has proved successful for hearing weak signals under noisy receiving conditions. Some transceivers have a earphone socket, others can be modified to have one. If you want this facility, check on its availability and order as necessary. see also para. 5.2.5. If you expect to use the transceiver on both the mains and DC battery operation from time to time, find out what is involved in changing from one to the other. Is it by a switch, changing plugs or soldering wires? Will a separate unit for operation on AC mains be required? Some transceivers have their AC power supply unit built into them, others do not. External power supply units require interconnecting cables, plugs and sockets, all of which can wear out or be damaged and thus be a source of failure.
5.2.1.4. Future availability
It is wise to standardise on one model of transceiver if it has proved satisfactory but unwise to buy a model that is about to go out of production. This may be difficult as manufacturers do not always give advance notice when a model is being withdrawn. After production of a particular model has ceased spare parts are usually available for several years. Before you buy the equipment write to the manufacturer and ask for how many years are they going to supply spare parts. You may get a more realistic answer to a written question whereas an enthusiastic salesman's response to a verbal question may be: "No problem, spares will be available for the next ten years!" Two years later when that particular salesman has left the company there could be difficulty in obtaining spares. You will need to consider how easily and rapidly you will be able to communicate with the manufacturer. Do you have a common language in which to discuss technical questions? How rapidly can you obtain equipment and spares? It may be advantageous to select a manufacturer, or certainly an agent, in the country in which you are working or in your home country. With foreign manufacturers you will be subject to fluctuations in the exchange rate when performing currency transfers. It should be noted that whoever you are dealing with, you will possibly encounter delays in the postal system when enquiring or ordering from overseas.
5.2.1.5. Protection
You should enquire if there are any protective devices built into the transceiver to protect it from damage by lightening. These usually take the form of diodes which give limited protection, in practice the aerial ought always to be disconnected from the set when it is not in use. see para.7.2.2.5. Some transceivers are "reverse polarity protected" i.e. the 12 volt DC supply can be connected to the transceiver the wrong way round without damaging it. See para.5.2.5.
5.2.1.6. Channel Frequencies
Transceivers which are not synthesised only have a limited number of channels see para. 3.1 and 3.1.3. For these you will need to specify the required frequencies for each channel, including whether it is USB and/or LSB, and you will need to choose a transceiver which will provide the necessary number of channels.
First you must list the frequencies which have been authorised for use by your own group.
Secondly you may need the authorised frequency of some other groups. e.g. MAF frequency for a location with an airstrip.
Thirdly there may be certain frequencies on which you want to listen i.e. receive but not transmit. List these as channel frequencies but qualify with RECEIVE ONLY. For example, there may be members of your organisation in another nearby country with whom you are not permitted to communicate by radio. However you can listen to their transmissions on their particular frequency and similarly they could listen to you. Note if you have for personal use a short-wave broadcast receiver, preferably digital, that has a SSB facility you could use this to listen to any frequency.
Fourthly if the country in which you are operating permits amateur radio and you have or are likely to have radio amateurs in your group then you could allocate one or two channels to amateur frequencies. Such channels have been used in the past with some success in Africa for a missionary net on 14.19 MHz. The merit of this arrangement is that a limited amateur facility is provided at the cost of one or two extra channels rather than the cost of a complete amateur transceiver. The reverse has also been done when amateur transceivers have been successfully modified to provide the authorised mission frequencies.
Lastly you ought to have at least one channel, possibly two, spare for future use as you may well find at a later date that it is necessary to add a further frequency. So now you should know the number of channels you will need and you will be able to select a transceiver that satisfies your demand. There are two frequencies associated with a channel. There is the CHANNEL frequency which is the actual frequency transmitted and there is the CRYSTAL frequency which is often 1650 KHz higher than the CHANNEL frequency. When ordering crystals for a additional channel or for replacement, either definitely state which frequency you are giving or state both the channel and crystal frequency.
5.2.1.7. Microphones
The most expensive transceiver and elaborate aerial system will not permit you to speak to anyone if your microphone fails!. Although the microphone is one of the least expensive items of a radio system many people try to save money and buy cheap ones, often with disastrous results. Prices in 1988 for hand-held or "fist" microphones varied from £12 to £36. When a hand-held microphone is in use there is continual movement, both of it and of its connecting cable. There is also the temptation of passing it from one speaker to another often involving the stretching of its cable to its furthest extent! It is also easy to put it down carelessly or even to drop it on to a table or desk or to let it swing from the end of its cable. All this constant wear and the occasional bump is often the cause of failures which could be avoided if a desk microphone is used which can cost £60 to £85. They are normally left in the same position on the desk or table and apart from pressing the on/off switch at the beginning and end of your message it does not need to be handled.If considered necessary a desk microphone can be securely fastened to the desk. It is recommended that you use a desk microphone and also have a hand-held one as a spare. In any case you should always keep a spare one available as it such an essential part of your equipment. Microphone types are classified as dynamic or ceramic and their impedance as high, medium and low. You will need the microphone to be compatible with the stated needs of the transmitter, in other words the manufacturer will tell you what sort of microphone you must use with a particular transceiver. See also suggested microphone modifications in para.5.2.5.2.
5.2.1.8. Power Requirements
Transceivers are available to operate from either one or more voltages e.g. 12v DC, 110 or 220 to 240v AC. If the transceiver circuits operate from 12v DC then an additional power unit is necessary for operation from 230v AC. Conversely a transceiver requiring 230v AC will need a power unit for it to operate on 12v DC. These units will either be inside the transceiver case or in a separate case connected by a cable.
5.2.2. Aerials
For a single channel set a single aerial will most likely satisfy your need but it will depend on your directional needs. See para.2.2.3 and 4. A single dipole can be used for all frequencies within +2% or -2% of the centre frequency for which it was cut, see para.2.2.1. Up to four dipoles can be combined with in multipurpose configuration to cover a range of frequencies see para.2.6.1. A broadband aerial, see para.2.6.2. should be considered for more than two frequencies as its cost can be competitive. Check that the all weather power rating of the aerial is sufficient for the power you will be transmitting. This is unlikely to be problem as aerial ratings of 1Kw. PEP. and above are common and your transmitted power may be a maximum of 150w. PEP.
5.2.3. Power Sources
It is the externals to the transceiver that often cause the failure of a radio station e.g. microphone or power supply. Table 5.2. can be used for selecting a reliable and suitable source of electric power. For more detailed information on each source read para. 3.2. on Power Supplies. In particular note that if you choose solar power it is an advantage to have done your own calculations to obtain an estimate of your needs before you buy the panels see Para.3.2.4. One user found that the quantity of solar panels they had purchased on the advice of the supplier were insufficient for the task they had specified. It was later discovered that the supplier had intentionally underestimated the need in order to quote a lower and more competitive price. The result was that they had to buy more panels at a later date after experiencing frustrating delays in setting up their operation.
Table 5.1. Selection of Power Source.
5.2.4. Test equipment
A simple item of test equipment is the multimeter which measures voltage, current and resistance. The original multimeters consisted of a meter with a moving pointer (analogue type) and a range and function (voltage or current) selector switch. More recent versions have a numerical display (digital type) of three or four digits and automatic range selection, only requiring a function selector switch. Whilst digital displays are more robust than moving pointer types they do require a battery to power them. Examples of multimeter prices are:
Analogue type £20 to £150. Digital type £60 to £140.
Multimeters have proven useful wherever there is a radio because most people are capable of using them to measure mains or battery voltage and testing fuses. If you are equipping a radio workshop you can spend from £1,000 to £10,000. The choice of equipment should be made by the radio engineer who will have experience and preferences. A modest workshop would contain an oscilloscope (£300 to £600), a signal generator (£100 to £200), multimeter, SWR meters, transmitter dummy load, soldering irons and various tools. The amount of test equipment necessary can be minimised by using a spare transceiver as a transmitter to provide a test signal for a receiver being repaired, then as a receiver for testin a transmitter.
5.2.5. Modifications
If the modifications suggested in this section do not exist in the transceiver you select then they can usefully be added. This may be costly if performed by the radio manufacturers so you should first obtain a quotation for such work. Missions and aid agencies may have a radio engineer amongst their home base supporters who could do the modifications at low cost. However it is important to make sure a volunteer engineer is really competent to do the job before you let him touch your equipment! If you do have a radio engineer able to help you in the country where it is manufactured he could visit the manufacturer for the final testing of the equipment as this would be an excellent opportunity to check that your written specification has been interpreted as you wanted. If such a relationship with your manufacturer can be established it will give you confidence in their equipment and their ability to serve your future needs and it may be useful to them to have feedback from someone using their equipment in your particular area. Such an arrangement with one particular firm in UK as been of great help to the author. Suggested modifications will now be explained.
5.2.5.1. Reverse polarity protection
As everyone should know a 12v.DC battery (e.g. a car battery) has a positive terminal and a negative terminal. The power cable coming from your transceiver will have a positive lead which should be connected to the positive terminal and a negative lead which goes to the negative terminal. Many times these leads have been wrongly connected with disastrous results to transceivers resulting in having to replace expensive transistors. The leads on the cables should be labelled but labels can be removed and replaced incorrectly. They are also often colour-coded e.g. black negative red positive but different colours are used by different countries and by different manufacturers so causing mistakes to be made. The safest thing to do is to provide protection which will prevent the reversed voltage reaching any components should the wrong connection be made. Three methods of providing this reverse polarity protection will now be described.
5.2.5.2. Microphone switches
There may be several switches on your microphone, e.g. high-low impedance and VOX, which can usually be set and left in one position. Therefore it would be safer to fix these in the required position by altering their wiring. Impedance only on the switch shown in Figs. 5.5 and 5.6, it may appear that shorting pin A to C would be sufficient but Low Impedance could still be selected. Therefore it is necessary to remove the wire from Pin C and connect it to Pin A. If a transceiver has a VOX position it means that whenever you speak into the microphone you will automatically transmit without pressing the "press to talk" control providing the microphone is switched to VOX. If you do not have a VOX facility on your transceiver or if you will not be using VOX then the microphone VOX control should be wired to the normal position.
The "press to talk" control normally operates two switches inside the microphone as shown in Fig. 5.5. One switch shorts out or disconnects the microphone during reception. This is a facility not required in most modern transistor transceivers because the power is automatically removed from the microphone amplifier during reception. This switch causes problems when it does not make good contact and often one can hear transmissions going on and off every few seconds due to an intermittent contact. When the switch is not necessary the wires should be removed from it and the microphone permanently connected as shown in Fig. 5.6. This leaves the switch free for other use. The second (transmit) switch turns the transceiver on to transmit and should be left to operate normally. However the now disconnected microphone switch can be connected in parallel with the transmit switch as shown in Fig. 5.6. to give extra reliability.
5.2.5.3. Earphone socket
When earphones are plugged into their socket it is usual for the loudspeakers to be disconnected automatically. The earphones used should be of similar impedance to the loudspeaker they are replacing e.g. low impedance phones for a low impedance speaker.
5.2.5.4. Squelch
The squelch control, see para. 3.1.3., can present a problem to inexperienced operators. If the squelch control is set for high level signals then weaker ones can be missed altogether. One aid agency in Kinshasa requested the help of a radio engineer because they could no longer hear any of their other stations. On turning the squelch control on the front panel the engineer was able to hear all stations without any problems. There was no fault at all in the transceiver, the operator had actually set the squelch control so high that no stations could be heard. In situations where the squelch facility will not be used the control can be wired so that it is permanently off. This can be done by removing the wire from the "variable" arm of the control and soldering it to the "squelch off" end. To indicate that this has been done the squelch control knob can be removed from the front of the transceiver.
5.2.5.5. Power light
The simple power light, see para.3.1.3., can be replaced by a two state LED (indicator light). The LED can be green when the +12 volt DC supply is in excess of say 11.6 volts and then it changes colour to a flashing red when the voltage falls below that. Supporting circuitry is necessary to operate these LEDs but this indication is particularly useful when the transceiver is operated from a battery and no voltmeter is available. A competent radio engineer should be able to design such a circuit using transistors and zener diodes. A circuit used by the author is given in Fig.5.7. The LED was Radio Spares (RS) 588-112.
5.2.5.6. Internal connections
Maintenance of a transceiver can be carried out rapidly by a technician visiting a remote location if all the main components are on plug-in circuit boards. However some transmitter HF power amplifiers have their connections made via soldered wires e.g. the high current connection to the power supply. This can be modified so that the connections to the power amplifier are routed via plugs and sockets e.g. the power supply can be via high current snap-on car electrical type connectors.
5.2.5.7. Foot switch
This is simply a foot operated version of the microphone "press to talk" switch. Pressing the foot down on it causes the radio to transmit removing the foot returns the radio to receive. The foot switch can be wired in parallel with the existing "press to talk" switch on the microphone so that either can be used.