ABOUT UHF CB

(Ultra High Frequency CB Radio)

 

 
 Channel: Frequency: Use: Channel Spacing:
 Channel 1
 476.4250
 Duplex - Repeater Output 12.5 KHz
 Channel  2
 476.4500
 Duplex - Repeater Output 12.5 KHz
 Channel  3
 476.4750
 Duplex - Repeater Output
12.5 KHz
 Channel  4
 476.5000
 Duplex - Repeater Output
12.5 KHz
 Channel  5
 476.5250
 Duplex - Repeater Output     (Emergency use only)
12.5 KHz
 Channel  6
 476.5500
 Duplex - Repeater Output
12.5 KHz
 Channel  7
 476.5750
 Duplex - Repeater Output
12.5 KHz
 Channel  8
 476.6000
 Duplex - Repeater Output
12.5 KHz
 Channel  9
 476.6250
 Simplex
12.5 KHz
 Channel  10
 476.6500
 Simplex     4WD Drivers - Convoy, Clubs & National Parks
12.5 KHz
 Channel  11
 476.6750
 Simplex     Call Channel
12.5 KHz
 Channel  12
 476.7000
 Simplex
12.5 KHz
 Channel  13
 476.7250
 Simplex
12.5 KHz
 Channel  14
 476.7500
 Simplex
12.5 KHz
 Channel  15
 476.7750
 Simplex
12.5 KHz
 Channel  16
 476.8000
 Simplex
12.5 KHz
 Channel  17
 476.8250
 Simplex
12.5 KHz
 Channel  18
 476.8500
 Simplex     Caravan & Campers Convoy Channel
12.5 KHz
 Channel  19
 476.8750
 Simplex
12.5 KHz
 Channel  20
 476.9000
 Simplex
12.5 KHz
 Channel  21
 476.9250
 Simplex
12.5 KHz
 Channel  22
 476.9500
 Data Only (No Voice - No Packet)
25 KHz
 Channel  23
 476.9750
 Data Only (No Voice - No Packet)
25 KHz
 Channel  24
 477.0000
 Simplex
12.5 KHz
 Channel  25
 477.0250
 Simplex
12.5 KHz
 Channel  26
 477.0500
 Simplex
12.5 KHz
 Channel  27
 477.0750
 Simplex
12.5 KHz
 Channel  28
 477.1000
 Simplex
12.5 KHz
 Channel  29
 477.1250
 Simplex     Pacific Hwy (NSW) & Bruce Hwy (Qld) Road Channel
12.5 KHz
 Channel  30
 477.1500
 Simplex
12.5 KHz
 Channel  31
 477.1750
 Repeater Input
12.5 KHz
 Channel  32
 477.2000
 Repeater Input
12.5 KHz
 Channel  33
 477.2250
 Repeater Input
12.5 KHz
 Channel  34
 477.2500
 Repeater Input
12.5 KHz
 Channel  35
 477.2750
 Repeater Input (Emergency Use Only)
12.5 KHz
 Channel  36
 477.3000
 Repeater Input
12.5 KHz
 Channel  37
 477.3250
 Repeater Input
12.5 KHz
 Channel  38
 477.3500
 Repeater Input
12.5 KHz
 Channel  39
 477.3750
 Simplex
12.5 KHz
 Channel  40
 477.4000
 Simplex     Highway Channel
12.5 KHz
 Channel  41
 476.4375
 Duplex - Repeater Output
12.5 KHz
 Channel  42
 476.4625
 Duplex - Repeater Output
12.5 KHz
 Channel  43
 476.4875
 Duplex - Repeater Output
12.5 KHz
 Channel  44
 476.5125
 Duplex - Repeater Output
12.5 KHz
 Channel  45
 476.5375
 Duplex - Repeater Output
12.5 KHz
 Channel  46
 476.5625
 Duplex - Repeater Output
12.5 KHz
 Channel  47
 476.5875
 Duplex - Repeater Output
12.5 KHz
 Channel  48
 476.6125
 Duplex - Repeater Output
12.5 KHz
 Channel  49
 476.6375
 Simplex
12.5 KHz
 Channel  50
 476.6625
 Simplex
12.5 KHz
 Channel  51
 476.6875
 Simplex
12.5 KHz
 Channel  52
 476.7125
 Simplex
12.5 KHz
 Channel  53
 476.7375
 Simplex
12.5 KHz
 Channel  54
 476.7625
 Simplex
12.5 KHz
 Channel  55
 476.7875
 Simplex
12.5 KHz
 Channel  56
 476.8125
 Simplex
12.5 KHz
 Channel  57
 476.8375
 Simplex
12.5 KHz
 Channel  58
 476.8625
 Simplex
12.5 KHz
 Channel  59
 476.8875
 Simplex
12.5 KHz
 Channel  60
 476.9125
 Simplex
12.5 KHz
 Channel  61
 
 Reserved for Future Expansion

 Channel  62
 
 Reserved for Future Expansion

 Channel  63
 
 Reserved for Future Expansion

 Channel  64
 477.0125
 Simplex
12.5 KHz
 Channel  65
 477.0375
 Simplex
12.5 KHz
 Channel  66
 477.0625
 Simplex
12.5 KHz
 Channel  67
 477.0875
 Simplex
12.5 KHz
 Channel  68
 477.1125
 Simplex
12.5 KHz
 Channel  69
 477.1375
 Simplex
12.5 KHz
 Channel  70
 477.1625
 Simplex
12.5 KHz
 Channel  71
 477.1875
 Repeater Input
12.5 KHz
 Channel  72
 477.2125
 Repeater Input
12.5 KHz
 Channel  73
 477.2375
 Repeater Input
12.5 KHz
 Channel  74
 477.2625
 Repeater Input
12.5 KHz
 Channel  75
 477.2875
 Repeater Input
12.5 KHz
 Channel  76
 477.3125
 Repeater Input
12.5 KHz
 Channel  77
 477.3375
 Repeater Input
12.5 KHz
 Channel  78
 477.3625
 Repeater Input
12.5 KHz
 Channel  79
 477.3875
 Simplex
12.5 KHz
 Channel  80
 477.4125
 Simplex
12.5 KHz
 
Licenses for Repeater Channels 44 & 45 will not be licensed for an additional 6 to 12 months to allow extra time for owners of Channel 5 Emergency repeaters to upgrade equipment to meet the new standards   

Channels 1 to 8 and 41 to 48 - Repeater Channels Press the DUPLEX button on your radio to used any available repeaters
Channel 5 & 35 - Emergency use only - Monitored by Volunteers, No general conversations are to take place on this channel
Channels 22 & 23 - Data transmissions only (Excluding Packet)
Channels 31 to 38 and 71 to 78 - Repeater inputs - Do not use these channels for simplex transmissions as you will interfere with conversations on channels 1 to 8 and 41 to 48
 
The Australian Government has legislated that channels 5 & 35 on the UHF CB Band are reserved for emergency use only 
As at January 2007 the maximum penalties for the misuse of the legally allocated CB emergency channels are:
  • For general misuse - if an individual 2 years imprisonment, otherwise $165,000 (a $220 on-the-spot fine can be issued in minor cases); or
  • For interference to an Emergency call - if an individual 5 years imprisonment, otherwise $550,000 
 
If you interfere with another persons conversation just select another channel and do not provoke troublemakers that may deliberately search out other people provoke a reaction, Just ignore them.
 

.

Duplex, Simplex & repeaters....What do these mean?

Simplex - One way communication only. There is only one transmission and no reply expected.

Half-Duplex - Two way communications, however only one transmission at a time.

Full-duplex - Two way simultaneous communication. Both stations can talk and receive at the same time. Such as Telephones.

On UHF CB when repeaters are used it's termed duplex, and when repeaters aren't used it's termed simplex. So they actually both represent half-duplex transmissions on CB but are used only used to differentiate between repeater usage and non-repeater usage.

A repeater is a special type of radio, it receives a signal on one channel, but gives it out on another channel. That is why you need 'Duplex' on 477MHz C.B. So you can access the repeaters and make use of them. The C.B will display channel 1, because that is what you are receiving, but if you are using 'Duplex', then you are transmitting on 31 and receiving on 1. That is because the repeater receives signals on channel 31 and re-tranmsits the signals on channel 1. The repeaters are also allowed to be more powerful than just a standard CB, because the purpose of the repeater is to extend communicaion range. Here is a diagram:


Limit on power.

UHF CB radios are generally short range radios, and the Australian Government decided to limit the power of the CB radios so people couldn't talk too far and so I suppose there wouldn't be over crowding of the band due to a lot of high powered stations talking. The UHF radios are limited to no more than 5W coming out of the back of the radio.

The signal from a CB transmitter goes through coaxial cable to an aerial. Maybe not just one aerial, perhaps 2 or 3 aerials. Not all at once of course, one aerial at a time. Perhaps aerials with different polarisations, radiation patterns, and gains.

Aerials have different names, for instance:

Yagi Beam or just "Yagi" or "Beam", Dipole, Helical Whip or just Whip and some others.

Various antennas for 477MHz CB.

The length of the antenna for 477MHz CB is extremely critical, the wavelength of 477MHz is around 62cm. For this reason many 477MHz "whips" come out of the factory pre-tuned. Quarter wave ground planes are the most basic whips. They are constructed of stainless steel or wire, for more flexibility. At 15cm length they are relativley small. Quarter-wave antennae have a naturally high angle of radiation (explained later) and are best used in hilly country and with repeaters, as they are ideal for carrying the mobile signal from a low point such as your vehicle up to a repeater on the top of a mountain or city building.

The best mount position for a quarter wave is in the middle of any groundplane surface that can offer at least the radius of the whip and is unobstructed, such as the middle of the car's metal roof.

Centre-loaded helical whips are the next step up, with gain figures varying from 3dB to 4.5dB. This will give you a relatively good "flat" signal component for direct car-to-car or simplex range, as wall as a good angle for accessing repeaters.

Dipoles are the next step up, from a fairly middle-of-the-road 3dB to centre-loaded whips with a high gain figure of some 6dB.

The higher gain causes a flatter radiation angle resulting in more ground-plane aspect for your signal. This longer direct travel is achieved over flat terrain, and the range can be quite stunning in the country-however, a mobile in hilly areas would find themselves at a distinct disadvantage with a high-gain whip, especially where repeater access is needed.

Base stations.

Here, the choice is much simpler.

Almost all 477MHz base antennae other than directional beams or "Yagi" arrays are of "co-linear" design. These vertical omni-directional antennae are usually manufactured from fibreglass and aluminium, and the main variant outside the construction and materials used is their gain figure.

The most common figures are 6dB, 9dB and 12dB. Which one is right for you? It depends almost entirely on the surrounding terrain. The general rule is that the flatter the land around your station, the less the gain required.


Yagi Antennas.

Much like the Yagi-uda beam, this aerial gives extra range, either to talk through a repeater or stretch your simplex talk-distance. They are just a lot smaller because the wavelength is a lot smaller. Beam antennae effectively harness the limited output of 477MHz CB stations and also cut down on interference from other stations that may be on the same channel although not along a direct path between the two stations. Due to the fact that they concentrate signals in one direction only when horizontally polarized they enhance the range in that direction only and signals coming into the back of the aerial are attenuated.

Co-Axial cable for 477MHz

Cable is your radio's lifeline through which the RF flows.

There are 4 common cable specifications, each of 50ohm impediance (the resistance of the cable formed by some factors.), and their loss figures are rated on a 30m run.

The thinnest cable, and the one most suitable for mobile installations, is RG-58U or the superior RG-58C/U. RG-58 has a loss of 13.5dB over 30 metres at UHF CB frequencies, so even a 15m run there's a fair bit of loss. RG-213 is the most commonly used for base stations and represents an improvement of massive proportions over the RG-58 family. It has a loss factor of only 5dB over 30m, although after adding a few in-line connectors and other things, the figure will come to a good 6dB.

That is all I have about UHF CB radio. I hope you enjoyed and gained something from this information. Thankyou for reading!