If you spend any time at all on one of the many online forums you will hear quite a lot of chatter from folks complaining that their new VHF radio does not work as well as it should. All too often it seems, many boaters go out and buy a new radio because the old one did not work, come back to the boat then screw in the existing antenna cable to the new radio, then wonder why the new radio is no better than the old one. In many cases the problem was never with the radio but the antenna. The theoretical maximum output from a fixed VHF radio is 25 watts and in an ideal world we would be getting all of this transmitting power radiating from the antenna. Sadly, however, we do not live in an ideal world and the chances of sending all those 25 watts out into the ether are the stuff of pipe dreams and legend.
There are 4 basic components in the chain from the radio to the antenna; the plug that screws into the back of the set, the coaxial cable that connects to this plug, the connection at the base of the antenna and then the antenna itself. All or any of these components, if not working correctly, affect radio performance. Let's briefly discuss antennas. There are several types of antennas but these can be essentially broken down into those for sailboats and those for powerboats. A sailboat tends to move about more than a powerboat at sea, it heels to the wind and the antenna is often placed at the top of the mast where movement is greatest. This is perfect in many ways for a VHF as transmissions are effectively line of sight, so the higher the antenna the farther the signal will be carried. Typically an antenna for a sailboat will have what is known as a 'gain' of 3db. You can read more on gain and what that means here. A powerboat, on the other hand, tends to have an antenna that is lower to the water level than a sailboat, and this antenna will be longer in length and have a gain in the 6 db category. It also means that for a sailboat the quality of the cable to the antenna is of vital importance, it's important on a powerboat too, but it is not uncommon for an antenna cable on a sailboat to be almost 100 feet long. Any resistance or loss of signal strength in the coax cable will therefore likely to be significant unless it is of the best quality.
Coax cable comes in different gauges and thicker is generally better but the thinner types are often easier for pulling through the boat. Irrespective of the thickness of the cable they need to be made off, at least at one end, and sometimes both ends with a connector which screws into the antenna outlet socket on the back of the radio. So to my main point - more transmission problems are attributable to poor or incorrect cable terminations than anything else. Connections must be of the highest order if you want to get the best possible performance out of your VHF radio. Often I hear complaints that the radio receives signals OK but as soon as the mic is keyed to transmit nothing happens or at best the signal is weak.
Shown below are two coax plugs for the end of a VHF cable. On the left is the very common Shakespeare style gold plug that is widely available in West Marine and other retailers. These fittings are pretty much junk in my opinion, connections are poor even when down exactly as outlined in the instructions. They are fitted to the cable end with a pair of pliers, the electrical continuity is suspect between the cable shield and squeeze together 'teeth' on the plug, and mechanically they are not very strong, and oh, did I mention that they are not at all waterproof and corrode in a mater of weeks further reducing their already poor performance.
The silver connector on the other hand is of the crimp on type, offers far better continuity and has a high degree of mechanical strength, it's easy to add a length of heat shrink to cover the ferrule and the end of the cable further increasing the strength of the joint and preventing moisture from wicking down the shield. This is all good, but you do need to invest in a specialist crimping tool specifically for coax cable, show in the top picture. I bought mine from a vendor on ebay for $32 and they work great. Incidentally the crimp on connectors are called PL 259 and these too are widely available online.
So the point is, that before you spend money after complaining that your VHF does not work, check out your connections, buy a good pair of crimpers and some proper PL 259 plugs. Even if you do install a new radio at least you will be sure that you are getting as much radiated output to the antenna as is possible.
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