CB Radio Q & A
UHF Radios are a great accessory in our vehicles or even homes enabling us to contact others in the community, such as roads users, truck drivers, and possibly someone who can come to our aid, especially in remote regions and if we can contact them because we have a good set-up UHF radio.
So, if your UHF CB radio reception is patchy and unreliable, that is often due to its poor setup.
What's the go what DB antenna should I use?
For simplicity in this UHF radio guide, measuring aerials gain is generally done in dBd or dBi. We’ll be explaining gain in dBi, simply because it’s easier to get our heads around, and the majority of aerials are advertised with just the dBi rating. The term dBi technically means ‘decibels relative to isotropic radiator’, however, the important bit for us, is the number. Think of dBi in aerials like a torch with a focusable beam, where the bulb or LED is your 5W UHF unit and the focusing ring is your aerial. The torch is still putting out the same 5W but if you focus the beam (say 9 dBi) and it goes a long way, only illuminating a small area way over the other side of camp, but you can’t see your feet or the roof of your awning. Go the other way with the focusing ring (say 3 dBi), and you can now see next door’s camp, your roof, your feet, and what the kids are up to, but you can’t see the Boobook owl 400m away anymore. That’s dBi in a nutshell.
High Gain - 6-9 db
These are usually the broom-handle-style aerials and are often fairly long. They’re great for long-distance on open plains and on the highway where the terrain is nice and flat. The doughnut on this one is flat and wide – so it’ll throw a long way with line-of-sight, but put a building, hill, or forest in the way and you’re going to have comms issues.
Mid Gain 3-6db
These fellas are usually the ‘black fishing rod blank with copper wrapping’ whip-style or the three-foot stainless-steel rod with a ‘pigs tail‘ in the middle. Anywhere in this dBi range is going to be a good compromise between distance, and terrain/obstructions to line-of-sight. The signal output of this range would closely resemble an actual doughnut – not too flat, but not perfectly round either – right in the middle. These are the all-rounders.
Low Gain 0-3db
These ones are more often seen in cities and in alpine/mountainous areas. The Unity part of the name just means that the aerial pattern radiates in all directions equally. They’re usually short, stubby, and have a heat-shrink coating. This aerial will push a signal quite happily over trees, mountains, buildings, whatever – but you’re sacrificing range to do it. Their doughnut is essentially perfectly round and it’ll bounce over hills (or 60-story buildings) as high as it will throw signal horizontally.
A general rule of thumb suggestion is either a CD34 or a 6.5bd elevated feed for general everyday around town use, if you are going to use it only in the bush then the CD34 or a 3db is a better solution
Location is really a compromise of best transmit location compared to where you can mount it on the vehicle. The best position is in the middle of the roof, but who wants to drill a hole in their roof. For ease of fitting, traditionally many people attach their CB aerial to their bull bar, but in doing so their vehicle creates an uneven radiation pattern spreading out behind the car and to one side if fitted to one side of the bull bar. Your signal forwards can also be shadowed by any vehicles in front of you. Ironically, poor antenna location means that only a low percentage of users realise their radio’s full potential. Even an expensive high-gain antenna projecting above the roof level from a bull bar suffers because antenna tips radiate very 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. In other words, the ideal place to achieve this is up on the vehicle’s roofline or roof racks. If you’re at ground level, on flat terrain, the horizon is about 5 km’s away. If there is nothing between your antenna and the visible horizon, that would be the limit of your transmission range, but if you raise your antenna by just 1 m (i.e. from your bull bar up onto your vehicles roof) you may increase the range over that visible horizon.