UHF CB Radios

Understanding UHF CB Radio
Max Erskine, a member of the Bi-Tone West Coast Caravan Club, has written this article with the hope that it will explain in laymen’s terms the intricacies of the UHF Radio which is growing in popularity among caravanners in Western Australian Clubs. Max spent 12 years in the RAAF as an engine fitter and 27 years in the 1960”s and early 1970”s (10 years of this in Woomera) working on and operating Jindivik the Australian designed pilotless aircraft. Max also lived in Nowra, NSW, for 19 years and operated Jindivik for the RAN at the Jervis Bay Range Facility in the ACT. In Nowra, Max served as an Emergency Operator for CREST and was Secretary of the South Coast Branch of the Wireless Institute Civil Emergency Network for several years. He is an avid amateur radio operator, now in his 13th year, and enjoys operating both voice and Packet (digital)) communications within the amateur bands. Ed.

UHF CB Radio is a designated part of the Radio Frequency Spectrum, administered by the Australian Communications Authority (ACA) that has been designated to operate on a ‘class licence.’ This means any individual has the privilege to purchase and operate an approved transceiver under the conditions specified by the ACA without requiring an operator’s licence. To prevent confusion and ensure satisfactory communications for every person that wishes to use this part of the Radio Band certain protocols have been laid down. In the past, when licence fees where required, the Government Authority (formerly Department of Communications) gave all licensed people a document setting out operating procedures. These are still required to be maintained and some breaches are treated very seriously by the ACA. Of course the normal law abiding citizen will not have any problems in this regard. Interfering with emergency communications on the designated emergency channels 5 & 35 would be considered a serious breach of operation. Using the radio in an abusive and threatening manner would also be a serious offence. The operating procedure of the UHF radio is similar to the AM type sets operating down in the HF (High Frequency) or 27 MHz (cycles per second) part of the Band.

Consult the handbook if required and switch the set on. The usual arrangement is an “on/off volume control” just like most mantle radio sets. Turn the volume up slightly and then find the “squelch” control. Turn this fully anti- clockwise. Select the channel change control and turn this to a channel that is not in use. (Nobody operating on it.) Now turn the squelch control clockwise slowly until the hiss from the speaker cuts out. Turn the control clockwise just a fraction of a turn (about 1 mm or less) more of a turn in the clockwise direction to ensure the radio is adequately squelched.

SO……. What is the squelch control?
Well, the old AM sets had a squelch control also but generally there was so much noise on the HF part of the frequency that by the time you “squelched” it out you couldn’t hear any other signal except stations transmitting at a very close distance to you. Please note that some of the later model transceivers have an auto squelch or a system that allows preset squelch stages. Consult your particular set’s handbook in setting these up.

Not so with UHF CB.

When you have set up the squelch control as previously described even a very faint signal will “break the squelch” and you will be able to “copy” what is being transmitted very clearly. Of course the volume control should be set to suit and this may require adjustment depending upon individual conditions, just like your sound system in your car requires adjustment in “audio” level from time to time. Please note that some of the later model transceivers have an auto squelch or a system that allows preset squelch stages. Consult your particular set’s handbook when setting up.

The UHF CB radio has 40 channels. Some of these channels have been allocated for certain purposes and, whilst the “rat bag” element in society will do as they please, it is required that informed law abiding citizens like ourselves operate in accordance with protocol. Therefore the following describes the allocated use of channels.

  • Channels 1 to 8 Repeater receiving channels (Duplex Operation)
  • Channel 11 Call channel (Used to call up another station and then go to a clear channel of mutual choice)
  • Channel 5 & 35 Emergency channels only
  • Channel 31 to 38 Repeater input channels (Duplex Operation)
  • Channel 40 Road or ‘Truckies’” channel
  • Channels 9, 10, 12 to 30 and 39 are general use channels, (if no one’s talking on them already)

A repeater is a transceiver located at an approved high vantage point and used to extend vastly the range of the UHF CB radio.

Your radio has a button on it marked “Duplex.” When this is selected (refer operating handbook) and the radio is set to a repeater channel (1 to 8) and there is a repeating station that can hear your transmitted signal, you will be able to transmit through the repeater. While your radio is set say on channel 3 and you press the PTT (Press to talk) button, the radio automatically transmits on channel 33, and when you “let go the PTT” it receives on channel 3. This is the same for all the repeater channels. Try pressing the button and seeing if you can hear a repeater station “come back to you.” (Not on channel 5 thank you.) How will you know if you an access a repeater station? You will hear the repeater transmit a Morse code ident and there will be a “tail” follows the letting go of the PTT. That is you will hear a “carrier” on the radio coming back to you from the repeater station. What is a carrier? It’s just a means in which the message we transmit can be carried on. Pushing the PTT sends out a carrier……… when we talk through the mike we transmit intelligence (hopefully) that “modulates” the “carrier” and arrives at all the other receivers that are within radio operating range. Don’t forget that anyone that is within radio range can hear your conversation (it’s not like our good old cell phone) and especially over a repeater perhaps hundreds of people can hear you. No personal details please.

While UHF CB is more expensive than the sets operating down in the HF allocated CB Band, and compared to AM type receivers (not those which have SSB) the advantages are certainly a much clearer reception – a slightly more powerful transmitter, 5 Watts Carrier Power as opposed to 4 Watts for AM. For our purposes in the Caravan Club they are the way to go as they give excellent results over the distances we need on the road when travelling together in convoy or passing in opposite directions and exchanging information. They remain quiet and unobtrusive during your whole trip if operating on most of the channels that are not allocated, although when passing through towns or sometimes out in the country you may hear the occasional farmer on the channel

Most definitely NOT. The Australian Communications Authority decrees that no one owns any part of the Spectrum (as everything between Ultra Violet and Infra Red and beyond is called) and under Government Legislation and worldwide accords, the ACA administers the use of it and in fact certain commercial parts of the radio band are quite expensive to “rent.” We really are fortunate to have a share (at no cost) of this part of the spectrum.

When not going through a repeating station it generally depends upon the type of terrain you are located in. Let’s consider the Nullabor. Two vehicles operating say 5 to 8 kms apart will generally have little trouble communicating with each other. If say one vehicle is on the top of a rise it may well be able to communicate 25 kms. A general rule with UHF is “line of sight’. If you can see the terrain the other vehicle is located in you should be able to communicate. You don’t actually have to be able to see the vehicle. Under certain conditions you may be able to communicate a lot further. Some of the factors that will determine just how good a signal you can send or receive is dependent upon what type of antenna you have (a ‘gain’ antenna or just a ‘¼ wave’) and where it is located on the vehicle. Also how well the radio installation has been carried out will be a factor in signal strength. If transmitting through a repeating station the range of your communications is dramatically increased, depending upon the location of the station. For example a repeater station located at Roleystone will be capable of being accessed from just about all over Perth but don’t expect to communicate from within the “Polly Pipe”.

Other functions on your radio may include “Scan”, Group Scan”, “CTCSS”.

This selection button causes the radio to “scan” all the channels from 1 to 40 and pause momentarily when it detects a “carrier.” This enables you to listen to see if there is any activity on any of the channels in your area.

Just scans your selected group of channels. (See your operating handbook on how to program your set to do this).


THis stands for “Continuous tone-coded squelch system.” What’s it for? Well, your radio won’t need to worry about it most likely as it is an “optional extra” when you are buying the radio in the first place and the radio has the compatibility to have the little “chip” fitted in it and the buttons on the front panel to select it. What CTCSS does is to “squelch out” all signals sent except those that are received from a person or persons that you wish to communicate with which have the facility in their radio to “open your squelch” so that you can hear them and not everyone else on that particular channel. Why would anybody want that system? Well, let’s suppose you are operating a courier service and you have UHF CB and have it set on channel 11 (the ‘Call’ channel). Everybody in Perth is using channel 11 to call up their wife, brother, mother in law, friends and then move to a free channel that no one else is using. Well, you can’t hear them and can enjoy listening to your classical music on your beaut sound system or whatever while all this chat is going on. When the dispatcher wants to talk to you and send you off on an errand all they do is press the CTCSS Tone button on their radio and that particular coded transmission “opens the squelch” on your radio and they can then communicate with you.

You’ll soon get the hang of this and be able to enjoy yourselves. As a Caravan Club member, it has been decreed that the Club will be using channel 18. This is just an agreement between caravan clubs and we have no special privileges on this channel what so ever. If you are going through a town and somebody is using it for their purpose, one should act as if someone was holding a conversation in a group. Remember also, that they cannot hear you while they have-the PTT pressed in. You can only communicate with others provided they are receiving and not transmitting. If you attempt to communicate while another station is transmitting usually all transmissions will be garbled by those who receive them and nothing will be understood. This is called “doubling.” It is good practice therefore; to allow several seconds pause in between “overs” to allow any person who may have urgent need to communicate to put in a “breaker” Therefore, in the event of an emergency maintain your cool until a suitable “break” occurs in the “overs” and put in something like “Breaker, I have an emergency situation!” All emergency situations take precedence in the order of Life Threatening as top priority and all stations are to assist. Do NOT interrupt an emergency signal and do let the person you consider as the most experienced or closest operator, handle the situation. If there isn’t anyone else or you do consider you are in the best position to assist…… Go for it. In the event of needing to call an emergency on channel 5, try first (especially in Perth Metropolitan Area) with Duplex selected (through the 5/35 repeater) as there is an emergency Repeater Station in Perth. If that fails to produce a result go to channel 5 Simplex (not through the repeater). I hope that this article has provided you with a greater insight into UHF CB operation.

Happy operating.

Max Erskine VK6XME