Tips: UHF radio essentials
Making the most of your UHF radio signal can be the difference between finding help and waiting for hours on the side of the road.
Minor issues can have dire consequences in remote areas and communications are vital. A UHF radio could be your only friend.
Many accuse CB radio of being of short-range, patchy and unreliable, but according to UHF installation specialist, Phil Pullem, that’s often due to poor set-up.
Phil owned an electrics outlet for 32 years, is an advisor to the SA government and has designed many communications products. He says that out of all the vehicle radio antenna installations he’s seen, only around 20 per cent realise the radio’s full potential.
UHF radio transmits best in a line of sight: in other words, if your antenna can ‘see’ a point, your radio can potentially transmit to it. Therefore, antenna location and type influence a radio’s performance.
"Many people attach their CB aerial to a ’roo bar, but in doing so their tow vehicle will create a shadow for the signal, spreading out behind the car, since the top of the bar is level with the bonnet," Phil said.
"It also can be shadowed by any vehicles or vans in front. Even an expensive tall antenna projecting above the roof level suffers from this problem because antenna tips radiate little energy."
The general rule of thumb is to place the bottom half of the aerial at a point where it can ‘see’ the greatest distance, even to the horizon if possible. The ideal place to achieve this is on the vehicle’s roof line or roof racks.
Phil believes a good CB antenna needs to be no more than 1m in length, and some mounting systems are hinged so the aerial can fold down as it comes in contact with overhanging foliage. A short antenna that can take the knocks of overhanging branches works much better than a long antenna mounted low down.
It’s also best to fix your antenna vertically. A sloping unit may look good, but its efficiency will suffer because an antenna’s broadcast is largely flat, like a dinner plate, radiating out from a central point at the base. If you tilt the antenna, one edge of that imaginary plate rises up into the air, while the opposite slopes down towards the ground. You’re only achieving maximum range at that notional horizon at two points at right angles to the highest and lowest points.
The closer the antenna is to vertical, the more effective it will be. A UHF antenna that bends as you drive may lose performance in motion, but should be fine when you’re stopped.
If you can’t attach your antenna to the roof, another option is to optimise your broadcast during an emergency.
A simple method is to uncouple the vehicle from your caravan and drive several hundred metres away so the van represents a reduced shadow to the signal. Or you could even drive up onto higher ground.
Alternatively, choose an antenna that is ground-independent, i.e., one that can be taken away from its mounting point on the vehicle and still work while connected with an extension cable. If you attach the mounting point to the end of an extension pole with sufficient cable, you can raise the antenna to a higher point.
At ground level, on flat terrain, the horizon is 5km away. If there is nothing between your antenna and the horizon, that would be the limit of your broadcast range, but if you raise your antenna by just 2m you double the range to 10km, and so on.
A single broomstick, or even two joined together, will help you gain the maximum height.
"You just need something light and simple, like sleeved plastic conduit and a length of coaxial cable [50 ohm RG58]," Phil explained. "And since it only has to be a few metres long, it doesn’t have to be expensive."
Your choice of antenna is also significant. For convoy-style touring, where you only wish to talk to and hear from vehicles within a kilometre or so in front of or behind you, a short rubberised antenna, between 150mm and 300mm, is fine. These quarter or half-wave antennae are less likely to strike overhead foliage (and be damaged when they do).
For long distance work, a full length aerial, up to 1m in length, is preferred. The longer antenna can usually be stowed in the vehicle for emergencies, or when setting up camp as a base radio for others in your group.
However, when you get into some more rugged country those shorter antennae have another benefit. As they shorten in length, the major transmission in an antenna is squashed up and down, inducing the transmitted signal to transform from a largely flat plate-like form to one that radiates up and down as well as horizontally, like a globe.
This means it can ‘bounce’ the signal off higher rocks, cliff faces and other landforms above and below, potentially transmitting to the far side of a ridge or hill, or in a valley below, well out of that line of sight. These bounced signals travel less than a line-of-sight signal, but in a valley, a signal from a big antenna just may not ‘get out’.
Phil also advises having a radio that is easily removed from the vehicle so that if necessary it, and its ground-independent antenna, can be carried, along with the vehicle’s battery, to higher ground for the maximum range.
With the right altitude and a clear line of sight, your UHF CB radio can have a range of more than 100km, covering 31,000 sq km, greatly enhancing your chance of finding someone to come to your aid.
It’s good to share this information with your fellow travellers – the most important person in this equation might be sitting next to you.
Don’t be fooled into thinking that a small hand-held CB radio is all you need. They generally only cover a radius of about a kilometre. However, Phil experimented with a 5W hand-held and managed to contact someone more than 300km away from the top of the Grampians, Vic. As I said, altitude is an important factor.
A quality CB system in a car can cover up to 3500 sq km, as long as you set it up properly.
All of this is ignoring the benefits of the repeater station network, which might give you coverage of between 20,000 and 70,000 sq km. To achieve this while travelling you will need a comprehensive understanding of your radio’s capabilities and the repeater system. But that’s another story.
"You can use UHF CB to call someone when you have a problem in a remote place," Phil said.
"Use it as a bridge between yourself and the locals, other travellers and the trucking community.
"You shouldn’t be afraid of truckies. A few maybe grumpy, but they know what it’s like to spend a long time at the wheel, understand local road conditions, and can be a big help on the open road when you want to get around them or they want to get around you.
"These are all people who can come to your aid if you can contact them with a well set-up UHF radio."
Source: Caravan World Jun 2011