Can UHF Radios be used in a Convoy?


Compact, license-free portable two-way radios have been around for some time now. They are license free because their transmitting power is so low – about 500 mW. That’s not enough to blow a feather off a window sill. And in my experience they are not adequate for convoy communications. But the test I did was a while back and there now are newer and better products on the market. For a convoy to communicate effectively, one needs a range of at least three kilometers, with five being an ideal minimum, with ten all that can be expected from any practical radio type. Most convoys operate on 27MGz (marine) or 29MGz (CB) which provide line of sight, three to eight kms range. VHF has longer range, but the radios are more complex and even then, the range is limited to not much more than 10 kilometers at best. UHF radios have the advantage of no licence fee and low cost. If they can be used for convoy operations, then they could easily be the radio of choice. I chose the  Zartek PMR UHF FM Transceiver ZA-708. This is their most advanced UHF offering. When transmitting from a portable radio inside a vehicle, the vehicle’s metal construction acts as a Faraday cage, suppressing any transmission. It was therefore essential that I should give the test radios the best advantage by fitting an external antenna, just as the 27, 29 or VHF radios would have to have.  Zartek offer such an antennae, with a magnetic mount. I also fitted their microphone extension. With this, the radio is used just like a larger unit, with hand-held mic, which also acts as a remote speaker. In this way the radio itself can be tucked out of sight. It’s just like operating a larger radio. But would the range be adequate? The test was done in Namibia. Greg van der Reis in his Land Cruiser drove ahead, counting up the kilometers. I stayed put, monitoring the signal. Cameras were running in both vehicles. One, two and three kilometers, with no degradation in signal at all. This was looking promising. Then Greg went over a rise, blocking off the line of sight. At four kilometers, it became very scratchy and at five, I could hear him, but no words were decipherable. At six kilometers, there was no transmission received at all. So, UHF radios can be used effectively in convoys. But an external antenna is essential. But there is something you are not supposed to know. A high-gain antenna can be used, which will increase the range even further. But because these are not strictly legal, the place where you bought your Zartek will not sell it. You’ll have to go to a radio shack store for that. How much will it increase the range? I reckon the external antennae more than doubled the range. Who knows what a high-gain will do. Andrew S White. June 2014. Contact Zartek South Africa. Click here zartec