Once you have chosen which type of radio you want, a decision needs to be made concerning coax and antennas. After building your awesome overland rig, you want tires on it, right? Not only do you want tires, you want tires that fit and are appropriate for the task at hand. Choice of transmission line, antenna selection, and antenna placement must be taken into consideration.
Coax, also known as transmission line, transfers the signal from the antenna to the radio and vice versa. Like most other things, there are many different brands and types on the market. As is the theme of Axles and Antennas, let’s keep this simple.
Your choice of coax needs to fit a few criteria and one is mandatory. The mandatory rule is that it needs to be 50 ohm. There is really no other way around it without it becoming a complex issue. Just look for 50 ohm.
Another criterion is that you should look for flexible coax. Coax will be twisted and contorted from the radio to the antenna, so you really don’t want to fight with the stiff kind. You also want coax that can take of harsh use. It is on a 4×4 after all!
You don’t really want to pay more than $1 a foot. Anything more expensive for such a short run of 20 feet or so is not warranted. Just don’t cheap out and buy the worst stuff out there so you can save a few bucks. Remember the tire analogy? Right.
Diameter of the outside of the coax is important too. You will be feeding the coax though all sorts of holes and if you have to drill, the last thing you want is a gigantic hole bored though your clean firewall.
What about line loss? Line loss is normally measured in dB per 100 feet. This means how much power you lose per 100 feet of coax. Decibels (db) is related to power in that 3dB would be half of a given amount of power. So if you have a 50 watt transmitter, then 3 dB would be 25 watts. This is also frequency specific. Line loss for the VHF bands is higher than the loss of the CB band.
So when choosing your coax, you want to make sure you minimize your line loss via extra-long runs or lower quality coax. Buying better coax means more power to your antenna. This is a two way street. Weak signals are lost in the coax from the antenna to the radio.
What should you buy? Axles and Antennas strongly recommends a type called RG-8x. This type of coax is normally very flexible, has acceptable amount of loss across all the bands and is small enough diameter to pass though lots of existing pass-throughs. As for pricing, even the most expensive brands normally retail for no more than a dollar per foot.