27MHz CBThis system utilises 40 channels in the High Frequency (HF) range, which covers 26.965Mhz to 27.405MHz. These CBs use Amplitude Modulation (AM) and they usually come with upper and lower sideband (SSB) which helps increase range and performance. AM and SSB are not compatible with one another and for this reason the AM mode is encouraged to be used on channels 1 to 14 and the SSB mode on channels 15 to 40. AM signals can sometimes be fairly noisy and distances can vary from 5km to 10km in normal conditions. When SSB is used on a channel, distances between 15km and 50km can be obtained.
UHF CBThis system has recently been restructured by the ACMA and now utilises 80 individual 12.5kHz wide channels in the Ultra High Frequency (UHF) range, which covers 476.425MHz to 477.4125MHz. If you own a 40 channel system, please read the special section below "New Rules" to clarify what you need to do
These CBs use Frequency Modulation (FM) and have become the preferred mode of operation for many. Since UHF signals travel in a straight line, the terrain plays an important part in how well the signal is transmitted or received. For example, the transmission will perform quite poorly if the signal is blocked by hilly or heavily forested areas. On flat terrains such as open countryside, distances between 5 and 20km may be achieved. Distances of up to 100km can be achieved if one or both UHF CB units are elevated on say a hilltop. UHF signals are less prone to power line noises and can also provide clear and crisp communications without the long distance interference which is evident on 27MHz signals. UHF CBs can utilise a repeater station that retransmits the signals onto another channel. This can provide much further coverage and can be handy when you are out in the bush and you want to scan and talk to other fellow trekkers.
New Rules & Standards for UHF Radio
In simple terms, all simplex voice channels will transition to 12.5 kHz bandwidth, with new repeater channels created in the space between the existing channels. Utilisation of the first 40 channels remains available to the public without applying for a licence and without fees. However, if you wish to use the new repeater channels 41 to 43 & 46 to 48 you will need to apply for a new licence. Currently, licenses for channels 44 & 45 will not be issued to allow owners of channel 5 emergency repeaters more time to upgrade equipment to meet the new standards. Once the ACMA confirms that most emergency repeaters have been converted, then the 44 & 45 licenses will be issued to applicants.
The only tiny catch under the licence is; all users must operate in the allowed frequency range on a shared and cooperated basis and those users are all subject to the same conditions outlined in the licence. This means you must understand which channels are reserved for emergency use etc. See information further on this page for channel allocations.
Unfortunately, MOST (but not all) of the old 40 channel UHF CB radios are not upgradeable to include the new 80 channels, which means that to access them you will need to by a new unit. With that said, there are a limitied range of units that can be unlocked - meaning they can be converted from the 40 channel system to the 80 channel system, so do a check of your existing model first before assuming you'll need to buy a new one. The good news is that the ACMA has given a six year phase-in period during which you can continue to keep using your current 25 kHz radio. Beaware however that if you purchase a new unit, that there will be good deals going on through until late 2012 with units being sold by retailers that are not compatible with the 80 channels system. The AMCA has allowed retailers a grace period to allow them to sell off old stock.
UHF Radio Technical StandardsAll UHF Radios must comply with a technical standard across the board for manufacturers and private hobbyists to adhere to. The three major concerns are:
- Transmitting power for UHF Radios must not exceed 5 watts
- Operation of UHF Radio stations must only employ FM or PM (Phase Modulation)
- Necessary bandwidth of UHF Radios must not exceed 16kHz
Interference ManagementIn some cases, interferences may occur when a CB is operating near television and radio receivers. The ACMA has produced several booklets and information brochures on how to resolve interference problems. At the end of the day, it comes down to fair cooperation with the affected television viewer or radio listener to resolving any issues.
Breaches of the Class LicenceThe operator will no longer be authorised to operate under the class licence and would be liable for prosecution if breaches such as: operating on a frequency which is not permitted and using an emergency channel for non emergency use.
RepeatersUHF repeaters are special transmitting/receiving stations that are usually located in high areas to allow extended coverage. These stations, which are usually owned by businesses, farmers and clubs, allow UHF users to use them to re-transmit their signal. It works when you press your microphone button with the “Duplex or Repeater” button selected also. You must transmit between channels 1 to 8 (and now you also have access to 41 to 48) because the “Duplex or Repeater” selection will add 30 channels and will now transmit to channels 31 to 38 (and now also 71 - 78) on the repeater. The repeater, which previously collected the signal on 31 to 38 (or 71 - 78), then switches to its output channel 1 to 8 (and 41 - 48) to transmit simultaneously to say another radio user on the other side of the hill.
This can be hard to describe with words but if you can picture a device that needs two frequencies to work and it needs to keep these input and output frequencies as far apart as possible to allow the simultaneous receive and transmit (i.e. 31 to 38 for the repeater's input and 1 to 8 for the repeater's output). The further apart these two frequencies, the easier it is to keep the transmitter circuitry from interfering with the receiver circuitry. Therefore, you should not transmit to a repeater on channels 31 to 38 nor the new repeaters on channels 71 - 78. Please respect the fact that repeaters are erected and maintained by private individuals and you should keep the usage relatively short.
UHF Radio Channel AllocationBelow you will find a list of UHF Radio channel allocations. There are many channels that have been established by law including the Emergency channel 5 and the data transmission channels 22 and 23. The new 80 channel system does not change the allocation use of these channels.
- 1 to 8 and 41 - 48: These channels, which are established by law, can be used when sending a signal to a repeater which will help increase the communication distance
- 5 - This channel, which is established by law, can be used by anyone but only in an emergency situation
- 9 - Used for conversations
- 10 - Used by 4WD enthusiasts, clubs, convoys and in national parks
- 11 - Calling channel. This channel, which is established by law, is used to call or locate another station. Parties will then switch to another channel to continue with their conversation
- 12 to 17 - Used for conversations
- 18 - Holiday maker’s communication channel (e.g. when in a convoy)
- 19 to 21 - Used for conversations
- 22 and 23 - These two channels are used for data transmissions and is established by law. Voice transmissions are not allowed on these two channels
- 24 to 30 - Used for conversations. Note Channel 29 is specifically as a road channel.
- 29 - for Pacific Hwy (NSW) and Bruce Hwy (Qld) communications which are mainly used by truck drivers and other highway users
- 31 to 38 - These channels, which are established by law, are received by a repeater and re-transmitted on channels 1 to 8 to help increase the communication distance
- 35 - Can be used in case of Emergencies also
- 39 - Used for conversations
- 40 - Highway Communications which are mainly used by truck drivers and other highway user.
- 41 to 48 - new channels (use same as 1-8) are established by law, can be used when sending a signal to a repeater which will help increase the communication distance
- 49 to 60 - new channels can be used for conversations.
- 61 to 63 - currently reserved for future expansion
- 64 to 70 - new channels can be used for conversations
- 71 to 78 - new channels, which are established by law, are received by a repeater and re-transmitted on new channels 41 to 48 to help increase the communication distance
- 79 to 80 - new channels can be used for conversations
Summary:Channels 1 to 8 and 41 - 48 are repeater channels. Press the duplex button on your radio to use any available repeaters.
Channels 5 & 35 - emergency use only
Channels 22 & 23 - data only
Channels 31 to 38 and 71 - 78 - are repeater inputs, do not use these channels for simplex transmissions as you can interfere with conversations on channels 1 to 8 and 41 to 48.
Telemetry & Telecommand SystemsThis technology describes the transmission of data and related information via a certain frequency such as infra red or UHF. By utilising telemetry and telecommand systems via UHF signals, farmers can remotely control the operation and function of various types of equipment such as electric fences, water pumps and dam levels from many kilometres away.
- Programmable Scan Function - Scans up to 40 user programmable channels with both Group and Open scan functions available
- Remote or Local Installation Options - This can be mounted either remotely using the separate control head, or locally with the control head attached to the main unit
- Unique Page/Transpond Mode - Allows you to transfer an incoming Selcall to another radio if your radio is unattended
- Quiet Mode - Selectable on individual channels, the Quiet mode prevents incoming signals from being heard on selected channels unless preceded by your selcall code
- Overvoltage Protection - Special overvoltage detection circuitry protects the radio and warns of excessive voltage conditions by flashing the display
- Extra Channels - EXTRA receive channels available
- Inbuilt Selcall - Selective Calling with 4 or 5 digit ANI and fully user adjustable 5 tone transmitted Selcall Ident. Some units may allow naming of Ident for easier caller identification
- User Selectable Priority Channel - Lets you programme your normal working or local repeater channel for instant recall at the press of a button
- Feature Disabling Function - Allows scanning, squelch, duplex and priority functions to be enabled or disabled to make the radio simpler to operate
- Individually Programmable Duplex function - User selectable for only those individual channels in your area that have repeaters, leaving the others free for use as extra simplex channels
- CTCSS Ready - A built-in Continuous Tone Coded Squelch System provides quiet channel operation
UHF AerialThe general rule of thumb when it comes to antennas is the higher the frequency the smaller the antenna. A good example is the antenna size of a mobile phone, which uses nearly twice the frequency of a UHF Radio. Good antenna performance is important because it can assist your reception and transmission greatly. Antennas are also be made to have gain, which will increase the Effective Radiated Power (ERP) of the CB.
Helical WhipThe wavelength of 477MHz is around 62cm and the length of the antenna is very critical. This is the main reason why many 477MHz “Whips” usually come out of the factory pre-tuned. The most basic type of whip antenna is the quarter wave ground plane, which are about 15cm in length and are made of stainless steel or wire, for more flexibility. These relatively small antennas have a naturally high angle of radiation and are best used in hilly countryside. They work well with repeaters because they are ideal for carrying the signal from a low point such as your vehicle to a high point where the repeater may be situated.
GainA 4.5 to 6 dB gain antenna is great for all types of terrain and is suitable for most situations. Gain is measured in decibels (dB) and the higher the gain, the more power can be transmitted. High gain antennas usually have coils wound into the steel or fibreglass rod, increasing the length considerably. The clear advantages are that a 5 watt radio with a 6dB antenna can perform like a 20 watt radio because 6dB results in 4 times more power.
InstallationMost UHF aerials require a ground plane, which means they should be mounted on top of a metal surface. The best spot in this regard would be the centre of your roof. Unfortunately for some people, this may not be a great idea because it could require drilling through the roof for installation. Travellers also prefer to utilise their roof rack space for carrying supplies. If the roof is not on the cards, then other good locations to mount an aerial can include: the roof gutter, side guard or on the bullbar, which is probably the most common.
Mounting the Head & TransceiverFor some units, the in-car mounting will be very easy if the head unit is remote and small, such as in these pictures. Transceivers can be mounted in a hidden position under the dash or in a roof console.
Co-Axial CableIn all types of UHF antennas, feedline loss can be a constant threat in regards to performance. Bad feedlines can swallow up half or more of your transmitting power and therefore degrading reception. Loss can be determined by length and quality of the feedlines, so the use of thicker co-axial cables over thinner ones is a much better option. Some common cable specifications, each being 50ohm impedance and the loss figures on a 30m run are listed below:
- RG-58U series including the RG-58C has a loss factor of 13.5dB over 30m
- RG-213 has a loss factor of 5dB over 30m
Terminating the Co-Axial CableIf you have never done this before it is really very easy. You will need a soldering iron and a sharp knife such as a stanley knife or similar. Click on the picture below to see a bigger and clearer shot of the steps involved.
- A - Carefully cut the black insulation away about 3 cm then cut the outer conductor leaving about 1cm
- B - Fold back the outer conductor
- C - Cut the inner insulation about 5 mm from the outer conductor
- D - Slide some heat shrink and the outer piece of the connector or the entire area, then screw the fitting over the exposed outer conductor
- F - Solder the inner conductor to the end of the fitting
- G - Slide up to other parts and screw it together then place the heat shrink over the end and heat it
TestingIf you have a multimeter then set it to Beep or resistance check say 200 Ohm range - remove the antenna from the base and make sure that there is no short circuit (i.e no beep or not 0.00 on the Ohms test).
Handheld UHF RadiosHandheld models are also popular with obvious advantages of portable, the high advances in electronic technology and their increased affordability. These CBs range from as little as $40 to over $400 and provide as much functionality as the base station CBs. There are some top end models that have a range of up to 12km with an impressive 5 watts of TX output power. As well as being lightweight, ruggedly built with waterproof construction, these CBs are no toy. These units can be very handy for travellers in a whole range of situations.
Usually sold in sets of 2 handheld units you can lend one unit to another vehicle/person to enable UHF communication in an instant such as in the following scenarios;
- passenger leaves vehicle to check the track ahead and can use handheld unit to communicate back to the vehicle with information
- search and resuce situations involving 2 people (or as many handheld units are available) spreading out in different directions used in conjunction with an installed UHF system in a vehicle is an effective and sensible capability you can coordinate if planning a remote trip
- one party may wish to stay behind at the campsite whilst another member goes boating, fishing, bushwalking etc.
With handhelds UHFs you have an extra level of safety and peace of mind when heading off on solo excursions away from the vehicle, or campsite for minimal cost.