TECH question. VHF v UHF

It sounds as if you are trying to compare the two types of CB available in Oz? If so AM CB does not use VHF, it uses HF at around 27MHz.

Your statement is, basically, correct although it's much more complex - as you might imagine. Quite why UHF has taken over and HF is virtually dead I'm not sure; certainly audio quality is better on UHF and it's much less susceptible to atmospheric interference etc but HF will have a greater range, although as the max power is 4W range tends to be limited without a serious antenna.

In the 4WD world CB is used, almost exclusively, for car to car comms; with distance rarely exceeding a few km so, given the better audio and smaller antenna, it's a good choice. Although in places like the High Country it's often all but useless - in the bottom of the valleys you'll frequently be lucky to get 2km from it.

Mike Harding

Yes and no. No doubt he who knows and comments on everything will expound at length so I'll give let that little crumpet, trumpet.
To answer the second question, the frequencies that are used for various services such as CB, are allocated by a Govt Dpt (ACMA).
There is no CB on VHF.
If you're referring to 27meg , thats HF and a different ballpark.

you will find that 27meg and vhf are mostly used in the marine enviroment. cheers

The "effective range" of UHF CB, officially called CRS for Citizens Radio Service, is frequently extended in many metro and larger country towns, and also in some outback locations, by the installation of repeaters on high ground. Repeaters can have a range of up to 60km or so because of this high placement. This means that UHF users can still talk to each other up to 120km away, or if your friend is over the far side of a hill or other object that intefers with line-of-sight communication. Repeaters all work on channels 1 to 8(only). Channel 5 is officially reserved for emergency communications. A list or where these repeaters are located is readily available from internet sources or any shop that sells the UHF radios. So you can see which channel to use where you are going, or are.
To operate a repeater you switch or programme your radio to "duplex" mode. Then the radio sends a signal up to the repeater on one frequency and re-transmits the signal back down on another. For example if you have the radio on Channel 1 duplex, then the radio sends the signal on Channel 31 and re-transmits it back on Channel 1, so anyone tuned to receive Channel 1 hears you. Hint, try to avoid transmitting on Channels 31 to 38 if you are likely to be anywhere near a repeater as you will also be heard all over the place on Channels 1 to 8.
VK5KP

VHF is dedicated Marine in Australia, it is line of site unless going through a good repeater. Range normally 10 nautical mile, but VHF radios are 25 watts compared to UHF 5 watts.
So why can't they make UHFs 25 watts, it a bit like marine gps plotters 5,7,10 inch screens, why can't we have that size in gps for vehicles?
Cheers Bruce

I deal with radio communications in the mines up here in Central Qld. We tend to see greater distances in the VHF Mid band (70 MHz) and VHF High band (160 MHz) than the UHF bands (400 - 520 MHz). Thats using 25W mobiles and 50W repeaters. The differences in distances are not all that great but can be up to an extra 20 kms in the 70 MHz band. You don't find too many mines that still operate at that frequency as most have shifted to the 160 MHz and 480 MHz bands but a lot of the Emergency Services and Councils still operate on 70 MHz.

The lower the frequency (typically 2-30 MHz or 'HF' band) the more ability one has to skip the signal for greater transmission distances. Depnds on frequency and time of day / night though.

As for interference I would say AM suffers more than FM therefore you will get interference on the old 27 MHz and HF sets moreso than the 477 MHz UHF sets (HF users, correct me if I am wrong).

UHF is more popular as when it comes to the unliscenced CB bands, you have the choice of 27 MHz AM or 477 MHz FM and 477 is much clearer and interference free but is also supported by a great repeater network.

Regards
David

Simply put, UHF is cheap, easy, standard and free (once you've got the radio).

With UHF, buy a radio for anything up to $500 and you're away. No licencing required, and they're standard so your mates, or anyone else with a UHF radio, can be easily contacted (assuming you're in range and on the same channel).

VHF requires licencing and you get assigned a frequency (I presume?), so although it's private and the range is generally better, you have to basically create your own network - make sure whoever you want to talk to has a radio programmed to your frequency. And that tends to require a more expensive radio (but not always), however it has to be programmed in most cases by a dealer.

For instance, yesterday we went over to victoria to fight some fires. Vic CFA has their own vhf frequencies, CFS shares them but uses different channels on the fireground, and there were independent outfits there; blue gum fire units, farm units, and a Cat challenger cutting a trail.
All the vic trucks, the farm units, Challenger, & the forestry guys had uhf as well as their own vhf, so to work together they just went to uhf ch 10. SA doesn't have uhf in their trucks as a rule (or at least we don't), so when we were trailing the cat & trying to contact a bloke 10m away, we had to call our command car on vhf, and they'd relay on uhf.

Next time, I'll take a uhf handheld, and I'll be able to contact the challenger, farm units, blue gum units, SAPOL (if they've got theirs turned on).

Much easier!

The lower the frequency the more the signal is able to bend and follow the earths curvature. Thats why HF has more range than VHF and UHF. UHF and above are virtually line-of-sight. In some circumstances UHF signal can bounce off the ionosphere and get better distance with a dead spot in the middle. Some old military nav systems used freqs as low as 13hz and had a range of halfway around the world.