29Mhz Radios Off Road

Section 1 (General)	Section 2 (Technical)
Radios	Electromagnetic Spectrum
Objectives of ORRA	The Radio Signal
The 29Mhz Band	Amplitude Modulation (AM)
Frequency Table	Single Side Band (SSB)
Kit	Antennas - General
Base Station Radios	Antennas - The 1/4 Wave
Mobile (Vehicle Mounted) Radios	The Loaded Antenna (Longer & Shorter than 1/4 wave.)
Portable (Hand Held) Radios	Antennas - Standing Wave Ratio (SWR)
Antennas	The Radio Itself.
Antenna Placement	Acronyms.
Antenna Fitment
Antenna Tuning
Multi-purpose Antennas
Magnetic Mount Antennas
Tips for Radio Fitment
Radio Frequency Interference (RFI)
Tips for Use
Radio Controls (AM & SSB)
Setting up your Transciever
Etiquette	[Back to Main Page]

Radios

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Objectives of ORRA

• Bringing together the Radio owners of member clubs of the AAWDC
• Establishing and maintaining Radio base stations and the proper running thereof
• Holding and arranging functions to encourage members in the proper use of their radios.
• Public service i.e. Accidents, Civil Emergency, etc.

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The 29Mhz Band

The 29MHz band stretches from 29.700 MHz to 29.999 MHz. There are 23 discrete fixed frequency channels numbered 1 to 23. The Off Road Radio Association is licensed to use three frequencies, (See Frequency Table Below.) in both AM and SSB mode (See Section 2 for AM/SSB discussion). We should be aware that this band is not for the exclusive use of the ORRA. We share it with many other users.

Other users of the 29mhz radio band include:

• The ski boat fraternity
• Civil Protection organisations (who also use commercial radio frequencies)
• The National Sea Rescue Institute (who also use commercial radio frequencies)
• Farming communities.
• The Land Rover Owners Club and the S.A. Jeep Club (both part of ORRA)
• Commercial businesses such as private ambulance services, security companies, delivery services,etc.

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Frequency Table

Recommended Channel	Frequency	Use
1 or 14	29,8725	General Open ORRA
2 or 16	29,8975	Open ORRA
7 or 15	29,8850	General ORRA (New)

The most used frequency seems to be 29,8975 - normally located on Channel 2 or 16.

Other 29Mhz frequencies of interest are:

Recommended Channel	Frequency	Use
3	29,7725	Ski Boat Open "A"
4	29,9350	Ski Boat Emergency
5	29,8350	Mountain
6	29,8475	Civil Defense
8	29,9725	Ski Boat "B"

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Kit

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Base Station Radios

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Mobile (Vehicle Mounted) Radios

When in use the user only has to have a microphone in hand. The microphone includes a push-to-talk button, which the user is required to push to place the radio in transmit mode. Releasing the button, automatically swops the mode to receive. There are many makes, Kenwood, Dragon, Icom, Philips, Yaesu, just to name a few. They are programmed to receive only the allowed channels, and in most cases are AM only (See Section 2 for description of AM and SSB).

Some of the Radios may be fitted with a SSB, Suppressed-Carrier Single Sideband option. However, one needs SSB functionality in both the transmitting and receiving sets to utilise this feature. SSB channels all the power into the voice signal (by removing the Carrier and one Side Band), thus can achieve up to 3 times the range of an AM set, for the same output power.

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Portable (Hand Held) Radios

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Antennas

Type	Pro's	Con's
Whip Antenna	Best Reception.	Excessive length, sways excessively and, due to it's strength, removes lights in parking garages.
Base Loaded	Good reception, does not sway excessively, fairly robust.	Longer than Top Loaded, so still tends to hit lights in parking garages.
Middle Loaded	Shorter Antenna, good reception.	Sways around badly due to weight of coil, low hanging branches tend to damage the coil.
Top Loaded	Shorter Antenna, excellent reception.	Sways around badly due to weight of coil, low hanging branches tend to damage the coil.

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Antenna Placement

The antenna should be mounted:

• As high as possible.
• As close to the center of the vehicle as possible.
• As far from interference from engine components as possible.
• Must be well earthed.
• Must not be "shielded" by vehicle surfaces.

Some of these are achievable even on our vehicles, but then we hit practical problems such as the antenna removing lights in parking garages, or getting wiped out by passing trees.

This really leaves us with three options.

The first option and also the worst from a reception point of view, is a base/middle or top loaded antenna fitted to one of the front fenders. In this case the top loaded antenna is normally the shortest and is short enough to miss most overhead lights etc, but sways around very badly. The reception is also affected by which fender it is located on, as the “ground plane” will be missing on one side thus giving worse reception to one side. Having said all that, this remains the most practical option for permanent mounting for recreational purposes. This will normally work for general convoy use, but severely restricts the range.

The second favoured option is to mount the antenna on the roof of the vehicle using a “Gutter Clamp”. The Gutter clamp makes the antenna removable and does not require holes to be drilled. A problem is that antennas are often destroyed by low hanging bushes and branches when fitted to roof racks and gutters. Here the choice of Antenna itself is open, but probably the best is the base loaded antenna due to its reduced “sprung” weight. This means that it will not sway as much and is mechanically more able to take the knocks.

This option will also provide different reception depending on which gutter is chosen, unless the vehicle is fitted with a gutter over the windscreen. Mounting the antenna in the centre of this gutter provides the almost ultimate spot. Some “Gutter Mounts” incorporate a method by which the antenna can be tilted without removing them from the gutter, should you wish to go into places with lower clearance.

The third option is to mount the Antenna on the Bush bar. This is a very practical mounting, does not require holes in the bodywork, but has severe restrictions in forward transmissions due to the lack of Ground Plane. Antennas should always be mounted so that the minimum length of the antenna is shielded by the vehicle’s bodywork.

Very Important: Never key the radio with the antenna tilted, removed, disconnected or touching any metallic parts of the vehicle, as this will most likely blow the output transistors of the radio.

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Antenna Fitment

• Beware that the antenna must be mounted so that the steel part of the antenna will never come into contact with parts of the vehicle while transmitting or the result will be damage to the radio.
• The Antenna cable does not normally have a Radio Adaptor fitted, so make sure that one has been supplied according to the requirements of your radio. This makes it easier to route the cable, as a smaller hole will be required.
• Before fitting the antenna to the vehicle ensure that the paint is removed from the clamping area (underneath, where it cant be seen) so that a good antenna earth will be established.
• Where antennas are mounted on a canopy, an earth braid (braided cable) may be required to connect the antenna base to the nearest vehicle bodywork. Steel canopies must be grounded to the body of the vehicle by means of an earth braid.
• Once the cable has been routed to the radio, the correct Adaptor can be fitted. This requires some skill with the soldering iron.
  Make sure that the co-axial earth screen does not touch the centre core, as this dead short will blow the output transistors of your radio at least. The connections must be electrically sound and mechanically strong to withstand vibration and movement. A short piece of “heat shrink” is recommended for finishing off the connection.

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Antenna Tuning

• The Antenna should be supplied with a Cutting Sheet. This will provide a clue to the correct Antenna length per frequency. Carefully study the Cutting sheet.
• Make sure you understand, the required length, from where to where it is to be measured, and that you are looking at the right frequency.
• Choose a Frequency in the middle of the range of frequencies you intend to use it on.
• Once you have determined these issues, proceed to cut the antenna at exactly (or a fraction longer) the indicated length. If you have an SWR meter available, cut the antenna 1 to 2 cm longer than required and then using the SWR meter, gradually cut small pieces off until achieving the best SWR.
  DO NOT CUT TOO MUCH OFF or you will ruin the antenna.

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Multi-purpose Antennas

• The Antenna Tuner / Matching Unit (Balun). This device allows the antenna to “tune” itself to the frequency of the radio and maintains an impedance of 50 Ohms at all times. Some power loss does occur and when working with a mere 5 Watts, this can be critical. When working on HAM applications where high power is applied, this loss is negligible, so this device is recommended for HAM use not 29MHz.
• Swopping Antennas. When purchasing antennas for your vehicle, buy one base and then select your antennas so that they all fit the same base. The Antenna Manufactures can help you with this. Basically this affords the luxury of one mounting point (or hole in the vehicle) and the ability to swop antenna’s according to the frequency spectrum of the radio in use. This method is a little more trouble, but ensures that you get all the power to the antenna and out into the atmosphere.

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Magnetic Mount Antennas

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Tips for Radio Fitment

• Radios can draw fairly high currents from the battery when transmitting as opposed to their relatively low current consumption while on standby. The electrical wiring must be able to provide for these surges, so use thicker wire over the shortest possible route, and include a fuse at the battery end of the positive wire. Do not connect into ignition switches or the vehicle fuse box.
  (It must be emphasised that any wiring connected to the battery MUST BE CONNECTED VIA A SUITABLY RATED FUSE! Failure to do this may result in a burned out vehicle, and an unsympathetic insurance company)
• Both Transceiver and Antenna must be well earthed to reduce spurious noise pickup. (If your radio interferes with your FM Receiver or GPS, check for bad earthing first)
• Ensure that you can see the dials easily from your driving position.
• At all times ensure that the connectors being used are of the right type and that they have been connected to the cables in the correct manner.
• If in doubt about a radio installation, get someone with the right skills to assist you or have it done by a professional. Do not take chances, as a bad installation can become a fire hazard.

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Radio Frequency Interference (RFI)

• Natural interference is caused by electrical storms, varying atmospheric conditions and sun spot activity.
• Man made interference comes from a great variety of sources including power lines, neon and other fluorescent lighting systems, in car electronic equipment, cell phone etc.
• Vehicle Interference may be caused by amongst others, un-suppressed ignition wiring, Alternators, Electrical Fuel pumps, ABS Brake gizmo’s, Electronic fuel injectors, (even on some diesels), Tyre and brake generated static, static build-up due to wind & dust action on antenna, etc.
  Most modern vehicles are quite well suppressed, and don’t cause much interference, however, as an example,…. Land Rover V8 fuel pumps, and Jeep 2,5litre Diesel Injectors are two known culprits for interference!

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Tips for Use

• Ensure antenna is connected and free from metallic parts of vehicle.
• Decide before departure, which frequency will be used by all vehicles on the trip.
• Ensure that all users know and understand the accepted radio practices and etiquette.
• When speaking keep the microphone close to the mouth, speak clearly and slowly.
• Release the Transmit button immediately on completing your message.
• Transmit your call sign at regular intervals.
• Display your call sign on your radio.
• If the radio is switched on, but reception appears to be dead, first ensure that the Squelch is properly adjusted. It may be necessary to turn it fully counter-clockwise to establish if there is any “static” on the frequency. Also check that you have selected the right frequency or channel.
• If the others cannot hear you, make sure that the microphone is plugged in. (this has really happened – more than once!)

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Radio Controls (AM & SSB)

• Volume - Adjusts the listener volume. Usually also includes the on / off switch.
• Squelch - Adjusts the threshold for incoming signals below which the audio circuits will mute, and above which the audio system will automatically switch on. Used to mute the radio when it is not receiving a signal.
• Channel Selector - Selects the operating channel, and thus the frequency.
• RF gain / ATT - Different radios either have a RF gain control or a RF attenuator switch. These controls are used to make the radio more or less sensitive depending on the operating conditions.
• Mic gain / DX mic - Adjust how much amplification is given to the microphone signal prior to the modulation process in a transmitter. Ideally used to set for maximum modulation of the carrier with no distortion.
• Delta tune / Clarifier / BFO (Rotating control) - Found only on a SSB transceiver. Used to clarify the received signal and take the “Donald Duck” out of the voice and make it intelligible.
• Delta Tune “+ 0 - ” (Switch) - Sometimes found on a regular AM radio. Allows the frequency of operation to be shifted slightly above or below the standard operating frequency of a given fixed channel.
• Noise limiter / noise blanker - Filter circuits that can be switched in to either reduce spurious noise or remove pulsed type ignition noise from the received signal. When used it compromises receiver sensitivity.
• Mode selector (USB, LSB, AM) - Selects the mode of operation (Upper Sideband modulation, Lower Sideband modulation, Amplitude Modulation.)
• Scan button. - On newer digitally controlled radios that have this function, this allows the radio to automatically scan through a range of frequencies or channels and look for the presence of a radio signal.

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Setting up your Transciever

1. Switch the set on and before keying the microphone, do the following:
2. Turn the Volume knob to about 75% Volume.
3. Select the desired channel, by turning the channel adjustment. The channel number should be displayed on the LED panel.
4. Set the Squelch knob to its lowest possible position. (We will set the squelch properly later.) You should hear a hissing sound.
5. Turn the Volume Knob until the volume of the hissing is audible but acceptable.
6. Set the power to the highest position, normally marked in Decibels (db). Most sets will have a 20 db and 40 db setting. The 40 db setting will provide the best transmission over a long distance, while for short distance convoy work, the 20 db setting will be fine. It will also prevent you “blasting” the other peoples radios, also called “over modulating”
7. If fitted with a Public Address (PA) option, switch it off, or to the Transmit (TX) position. The PA option is only used if the set has an external loudspeaker attached.
8. If you key the Transmit button on the microphone, the Transmit LED should light up indicating that you are transmitting and the level on the meter should indicate 5 Watts. Your friend should be able to receive your message and should respond to you audibly.
9. Now to the Squelch Adjustment. (Note: some radios are fitted with Automatic Squelch and thus the user cannot do the following adjustments.) While not transmitting and not receiving any signals, the “static” on the frequency is always present as the hissing noise. To stop the noise, turn the Squelch Knob slowly clockwise until it disappears. If you turn the knob back a fraction, it should re-appear.
   The correct setting is so that the static just disappears. If you now start the engine, the static levels will normally increase and thus the noise will reappear. Again, carefully adjust the Squelch higher until it disappears.
   While driving, the levels of static will vary from time to time and it may be necessary to re-adjust the Squelch accordingly. Some items that will interfere are overhead power cables and steel bridges. They are evidenced by a sudden “burst” of static, which disappears when you are clear of them.
   Do not reset the squelch for these occasions.
10. If you suddenly seem to have no reception, it is normally due to the Squelch being too high, so turn it fully off (normally counter-clockwise) and try again.
11. If the other station is almost out of range, you may have to turn the Squelch adjustment down, so that you can attempt to decipher the other vehicle’s transmission in-between the static noise.

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Etiquette

• Contrary to years gone by, it is completely acceptable to use your name as your Call Sign. If there is more than one “Jack” in the convoy, assign Jack1 and Jack2 (or even Jack Discovery and Jack Defender!) as call signs, or whatever means you wish to distinguish them from each other. When the vehicles are assigned specific places in the convoy, Alpha 1, Alpha 2... etc may work well.
• Remember that while you are holding the Transmit button, no-one else can use the frequency, so before transmitting, listen to ensure that the frequency is clear, before transmitting.
• Always ensure you have the other parties’ attention before making the full transmission as follows. First call “Jack, come in for Mike” or alternately “This is Mike calling Jack”. The other person should then answer, “Jack, reading you Mike” or “Jack standing by for Mike”. Once this has been established, continue with your transmission.
• Ending each transmission with “Over” is not absolutely necessary, but does indicate end-of-transmission to other users, and is considered polite.
• Between transmissions, allow other parties to “break-in”, by allowing a 3 to 4 second pause, before keying and replying to the previous transmission.
• Keep Transmissions short and to the point.
• Speak clearly, directly into the mic and hold the key down firmly all the time, while speaking.
• Keep a listening watch, and if you have to turn your volume down, first inform the convoy leader. Then remember to turn the volume up again and announce your return to the convoy leader.
• With very long convoys, or very bad terrain, it may be necessary to ask a vehicle in the middle to relay transmissions for the rearmost vehicles. In this case, ensure that the Radio Equipped vehicles are dispersed evenly throughout the convoy.
• The Convoy Leader must always remember to inform the non-radio vehicles of decisions taken on the radio, to keep them up to date on all issues.
• If you need to break in on a conversation, wait for the end of a transmission and key your mic, saying “Break, break, break”. Then release the key and wait for one the operators to invite you to continue.
• If you suspect that you have keyed your mic simultaneously with someone else, release it immediately and listen for the other transmission to end. After the appropriate pause, you can try to make contact again.
• Never, in normal situations, use the words “Mayday, Mayday, Mayday” on the radio, as they are reserved for life threatening situations only. Rather use the words, “need assistance”, “need medical assistance” or even “emergency” where the situation is non-life threatening.
• Beware of using the radio in game viewing conditions, you may scare the animals away or ruin someone’s videotape sound track.
• Do not allow children to use the equipment without supervision and be especially careful at border posts and roadblocks, not to make remarks that are in bad taste.
• Always ensure that your equipment is maintained in top condition, as it is really worrying even annoying when someone, who you had comms with previously, “disappears”.
• Most of all, be polite, courteous and don’t use bad language on the Air!

Although these guidelines may seem like a lot of effort, they make for easier communications and can make those long stretches on the road a lot of fun.

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Electromagnetic Spectrum

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The Radio Signal

• Amplitude modulation (AM) -Used by us on 29mhz. Cheap to manufacture but very susceptible to electrical interference and noise.
• Frequency modulation (FM) - Used for commercial two-way radio, amateur radio, broadcast. More expensive to manufacture but immune to electrical noise and interference.
• Single Side Band modulation (SSB) - Very efficient mode of modulation use extensively by radio amateurs. Not cheap when manufactured with a high level of stability.
• Pulse Width modulation (PWM) - Specialist modulation type used in digital data transmission. E.g. -personal pagers, satellite telemetry etc.
• Pulse Code Modulation (PCM) - Same application as PWM.

This paper will only deal with the two forms of modulation used in 29MHz equipment.

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Amplitude Modulation (AM)

• In a basic amplitude modulation system, the signal to be carried is mixed with a carrier signal in a mixer stage of a radio transmitter.
• This mixed signal is then filtered to derive only the required component, and fed to a power amplifier stage.
• The amplified result is again filtered and passed through a matching stage and on to the antenna system where it is radiated into space.
• In the receiver, the incoming RF signal is amplified and mixed with a local oscillator signal generated internally.
• Through appropriate filtering and mixing techniques, the modulating signal is extracted from the RF carrier, filtered and amplified to a level sufficient to drive a speaker.
• Relatively speaking, AM systems are simple to design and cheap to manufacture.
• These systems are however very susceptible to natural and man-made interference.
• AM is also not a very efficient modulating system resulting in a low level of effective radiated power for a given power consumption.

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Single Side Band (SSB)

• In AM, most of the RF energy is in the carrier, but at the receiver the carrier is filtered out and discarded. This is the reason for the AM system’s inherent inefficiency.
• In SSB, the carrier is deliberately suppressed at the transmitter, and then the system changes to utilise as much power in the sidebands as is possible.
• This mode of operation will generally result in a two to four fold increase in effective radiated power.
• The side effect of this however, is that both the transmitter and the receiver design is substantially more complicated, and thus more expensive.
• Also, if the design is kept simple to keep the cost down, then stability can become a problem and the advantage of SSB can be lost.

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Antennas - General

• A low power radio with a good antenna can often perform better than a high power radio with a bad antenna.
• Antenna length is critical to it’s operating frequency, under no circumstances can one say “... the longer the wire the better...”. There are only a few applications requiring special equipment where very long antennas are used.
• For our operation on 29MHz, the antenna length is vitally important for efficient operation.
• Apart from the antenna length, the physical attributes of an antenna will be dictated by the amount of RF power it is expected to handle when the radio is in transmit.
• It’s appearance is also a function of where on the vehicle and how it is going to be mounted.

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Antennas - The 1/4 Wave

• All antenna theory, design and manufacture is based on the starting point of the 1/4 wave radiator.
• From this theory, the simplest antenna that can be manufactured is the 1/4 wave dipole or the 1/4 wave whip antenna.
• On the 29mhz band a 1/4 wavelength is approx. 2750mm or ¼ of 11 Meters, which is the Wave-length of a 29MHz Transmission.

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The Loaded Antenna (Longer & Shorter than 1/4 wave.)

• A 1/4 wavelength antenna requires no special treatment and can be mounted on a mobile vehicle very simply. However not all people are prepared to fit a 2,75 meter long antenna onto their vehicle.
• Using an antenna length that is shorter than this 1/4 wavelength (or longer for that matter) requires a matching circuit that will ensure proper radiation of RF energy, as well as correct matching of the antenna to the radio.
• The simplest and most common matching technique is the introduction of a coil in the antenna’s length somewhere.
• Most of the short antennas used by members are the top loaded type, but centre and base loaded antennas are also available.
• Top loaded antennas work very well, but are susceptible to damage in the field.
• Base loaded antennas on the other hand are sensitive to the mounting location and can be difficult to tune.
• Shorter “loaded” antennas used on 29mhz suffer slightly on efficiency but this is not enough to outweigh the physical advantages of the installation in many instances.
• The choice of a long or a short antenna is generally personal and vehicle mounting dependant.

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Antennas - Standing Wave Ratio (SWR)

• The SWR measurement, when done correctly, is a quick and simple way of checking to see that the antenna is correctly matched to the radio.
• Although it is a very theoretical and technical subject, the SWR instrument is basically indicating how much if the generated RF power is being effectively radiated out into space by the antenna system.
• The function of the instrument is to indicate the ratio of RF power being fed into the antenna versus the amount of that RF power that is not being radiated successfully and is thus being reflected back into the transmitter.
• This reflected power can do damage to the transmitter electronics and should be kept to a minimum at all times.
• When the SWR is at it’s lowest reading, it means the antenna is successfully radiating all or most of the generated RF power, and little or none is being reflected back into the radio transmitter.

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The Radio Itself.

• Radio equipment is designed from the onset to operate in specific modulation modes and on specific frequencies. This means that equipment designed for a certain application cannot be easily converted or modified to work in other modes. 29MHz equipment is no exception.
• The design criteria for the 29MHz system, was for a low power, safe, cheap, short-range communication system and it is in this role that it works very well.
• Although a 29MHz set is a low power device it is strongly recommended that it be installed correctly to obtain optimum results.
• With a power output of only about 4 to 5 watts on AM and around 12 watts PEP on SSB, the radios are relatively cheap and do not need heavy cabling for high current draw.
• Unless used extensively in transmit mode a 29MHz radio should not run down a car battery. If uncertain, it may be advisable to start the vehicle every half an hour or so and let it run at a fast idle for around five minutes.
• Antennas are not very expensive or high tech and due again to the low power are not likely to cause RF injury if they accidentally come into contact with humans or animals while a radio is in transmit. High power antennas can administer a serious burn if touched while the mic is keyed.
• 29MHz radios are usually channelised and programmed to have the operating frequencies on fixed channel switch locations.
• A channelised radio makes operation very simple. But the user does need to know what frequency is programmed to what channel number, as this is not generally pre-defined.

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Acronyms.

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