UHF radios and aerials: gain, mounting and channel etiquette
Most people ask whether they need a proper fixed UHF or whether a handheld will do. The radio is the cheap part; the aerial decides whether anyone hears you. A modest fixed set with a well-chosen aerial mounted sensibly will out-perform an expensive handheld every time, because the handheld's stubby aerial is inside a metal box with you.
The other half of the answer is that a handheld is an excellent second radio and a poor only radio. Walking fifty metres up the track to spot a driver over an obstacle is genuinely useful, and so is having comms out of the vehicle. Buy the fixed set first, add the handheld later.
What UHF CB actually is
UHF CB is the licence-free two-way radio band Australians use in vehicles, on 477 MHz, with 80 channels. You don't apply for anything — use of the band is covered by a class licence, and any radio legally sold here already complies with it, including transmit power. Power isn't something you choose, tune or upgrade.
The arrangements have changed over the years, including the expansion in the number of channels, so for the authoritative current position go to the regulator's published class licence, not a forum or this guide.
The practical point is that UHF is essentially line of sight. It doesn't bend around hills. A ridge between two vehicles is a wall. That drives every aerial decision below.
Handheld, in-dash, or remote head
- Handhelds need no installation and work out of the vehicle, but a short aerial at chest height inside a steel cabin limits them badly, and they're typically lower powered. Fine across a convoy, useless across a valley.
- In-dash sets are the traditional fixed radio, mounted in a dash pocket or bracket and wired to vehicle power and an external aerial. Simple, robust, easy to service.
- Remote head or compact sets hide the electronics behind the dash and put the controls in the microphone. They suit modern dashes with nowhere for a full-size radio, which is most of them.
Whichever you pick, the external aerial buys the range. Radio brackets and dash pocket kits are often vehicle-specific — confirm the retailer lists the mount for your series and build date.
Gain is not power
This is the single most misunderstood thing in the category, and getting it wrong makes your radio worse, not better.
Gain does not amplify anything. The radio puts out the same energy regardless of the aerial. Gain describes how that energy is shaped. A low gain aerial radiates in a fat, roughly doughnut-shaped pattern. A high gain aerial squashes that pattern flat, concentrating energy into a thin disc close to the horizontal.
On dead flat, open ground that disc is exactly what you want, and a high gain aerial reaches much further. In hills, gullies and on side slopes it's the wrong tool. The other vehicle isn't on the horizontal plane, and worse, the moment your vehicle tilts the disc tilts with it — so on a climb you're transmitting into the dirt and the sky rather than at the bloke behind you.
One note on comparing figures. Manufacturers quote gain in dB against different references — you'll see dBi and dBd, and they're not directly comparable, so compare like with like. Aerial length correlates loosely with gain but not reliably.
So, roughly:
- Low gain — bush, hills, gorges, steep tracks, convoy work where everyone is close and the terrain is broken. The forgiving choice if the vehicle spends its life on angles.
- Mid gain — the compromise if you want one aerial and you do a bit of everything. Most people are best served here.
- High gain — long flat runs. Highway, desert, open plains, sitting behind a road train.
Plenty of serious tourers run a common base with two whips and swap them for the terrain. If that sounds fiddly, buy mid gain and stop thinking about it.
Mounting, and why your bull bar choice matters
Height beats everything. An aerial mounted high and clear of obstructions does more for your range than any amount of money spent on the radio.
Roof or gutter mounting performs best and is the most annoying to live with. You gain height and a metal roof acting as a ground plane, and lose it to carpark height limits and low branches. It usually means drilling and routing coax through the headlining.
Bull bar mounting is the most common answer in Australia and it's a compromise. The aerial sits low and the vehicle's own body shadows signals to the rear, but it survives branches and it's easy to reach. Bonnet and guard mounting sits between the two.
The bar connection matters more than people expect. Not every bar has an aerial mounting provision, and where it sits affects performance and how much of the aerial blocks your view over the bonnet. If a UHF is anywhere in your plans, ask about the aerial mount when you buy the bar — our bull bars guide covers what "bar only" leaves out.
One technical point decides what you can buy. Some aerials need a ground plane — a metal surface under them, like a roof or bonnet — to work as designed. Others are ground independent. Bar-mount positions frequently have no useful ground plane, so a ground independent aerial is usually what you want there. Fitting the wrong sort to a bar and wondering why the range is poor is very common.
Also: use a spring base if you drive in scrub, keep the aerial clear of roof racks and tents that shadow it, and check whether the whip will hit the garage door.
Coax, SWR and the things that kill radios
- Don't cut the coax to length. On many aerials the cable is part of the tuned system. Coil the excess loosely, not in a tight bundle against metal.
- Route it away from ignition and high-current wiring, and protect it where it passes through a panel.
- Have the SWR checked with a meter after installation. A poorly matched aerial reflects power back into the radio, and that's how transmitters die.
- Never transmit without an aerial connected. Same reason.
- Check the connector after a season of corrugations and dust. It's the most common fault.
Channels and etiquette
Some of this is regulated and some is convention. Know the difference.
Regulated, and not negotiable:
- Channel 5, and channel 35 as its duplex counterpart, are the emergency channels. Don't chat there, don't test there, and don't use 35 to reach a repeater.
- Channels 22 and 23 are for data and telemetry only. Voice transmission on them is not permitted.
- Some channels are duplex repeater channels. Using duplex means going through a repeater and covering a large area with your conversation, so don't use it for convoy chatter.
Convention, widely observed and worth following:
- Channel 11 is the calling channel. Call there, agree a working channel, then move off it.
- Channel 40 is the road channel most truck drivers monitor. Listen first, keep it brief.
- Channel 10 is commonly used by 4WD clubs and convoys.
- Channel 18 is commonly used by caravanners and campers.
Local conventions vary by region and route, so ask locally. The basics apply everywhere: listen before transmitting, press the button and pause half a second before speaking, keep it short, say who you are and who you're calling, and don't key over someone mid-sentence. Offensive language on the band is an offence, not bad manners.
One more: CTCSS or tone squelch is not privacy. It only stops your speaker opening for traffic without the matching tone. Everyone else still hears you, and you'll happily transmit over someone you can't hear.
What UHF is not
It is not an emergency beacon. Range is short, it depends on someone being in earshot on the right channel, and in remote Australia there is frequently nobody. If your trips take you beyond help, carry a personal locator beacon or satellite messenger and treat the UHF as a convenience.
Before you buy
- Buy the fixed set and the external aerial first. Add a handheld later as a second radio.
- Choose gain for the terrain you drive, and pick mid gain if you want one aerial for everything.
- Check whether the aerial needs a ground plane, and match that to your mounting position.
- If you're buying a bull bar, sort the aerial mount at the same time.
- Confirm the retailer lists the radio mount or bar bracket for your series and build date, and quote your VIN.
- Have the SWR checked after installation, and never transmit without the aerial connected.
- Learn the emergency and data channels before your first trip, and leave them alone.
- Carry a beacon or satellite messenger if you go remote. The UHF is not that.
This guide is general information, not fitting or engineering advice. Fitment, compliance and safety depend on your specific vehicle — confirm with the retailer and a qualified fitter before you buy.