Constructing an Improvised CB Radio Antenna, by Dim Tim

Thursday, Jan 17, 2008

I have put a great deal of the info I have gleaned from SurvivalBlog to good use in my own preps. To reciprocate, the following is one of hopefully many bits of survival information that I plan to pass along to all the readers, in the hope that it will help someone else.

A short time back I read a few posts on some survival communications issues, and found them to be very helpful. They also got me to thinking about something that I did back around the start of the eighties, that I believe would be a great piece of survival gear for the folks using Citizen's Band. (CB or 11 meter ) and some 10 meter users.

One day, I came upon the thought that if the radio still worked, but the antenna became lost or damaged, what would I do then? How would I be able to talk to my group, let alone listen in to any other chatter. Having a bit of electronic knowledge ( two year tech. degree in industrial electronics ) I set about to make an expedient antenna system from inexpensive, and commonly found materials. The result was a simple antenna that would work in a pinch, and was easy to transport, and would be as good as, or better than a commercial one. Enter the simple dipole antenna.

A dipole is a pair of wires or conductors connected to the "ground" and the center conductor of the coaxial antenna cable, and stretched out either in a vertical or a horizontal position. Most "whip " style mobile antennas are around 102" in length ( this is the number that antenna designers use in their standing wave ratio (SWR) to frequency calculations, to match an antenna to a particular radio to achieve maximum efficiency ). Using this as a reference point, I bought a 25' roll of solid aluminum clothesline wire at the hardware store, a small package of solderless, crimp style connectors, a small package of 1 1/4" wood screws, and a roll of electrical tape. The only other things you will need are a couple lengths of 550 paracord, two lengths of 1 1/2" dia. ( about 4-5" long ) dowel rod, and a 2x4 block about 6 to 8" long. To start, take the 2x4 block and 2 wood screws, and screw the wood screws only a couple of turns into the wood, placing one at each end, about an inch or so back from the ends. Next, take the coaxial antenna cable, and carefully strip back the outer jacket about 6" and undo the braided wire, and twist it into one individual length. Next, strip back the insulating jacket over the center conductor about 1/4". Attach a crimp connector to each wire, preferably by soldering, or by securely crimping with a pair of electrician's crimping pliers. Next, take and wrap the exposed, twisted, braided wire with a bit of the electrical tape.

Next, take a pair of wire cutters, and cut two 102"-long pieces of the clothesline, and make an eye hook at one end of each, and unscrew the wood screws on the 2x4 and attach one wire "eye" to each ( do not screw the screws down all the way yet.) Next, take the dowel rods, and drill a hole through the side about 1 1/2" from the end, and then the other, repeating the same for the other dowel. The holes should be large enough to thread one of the clothesline ends through one, and a piece of the paracord through the other for each one. Now, connect one of the coaxial antenna wire connectors to the wood screws on the 2x4 block and tighten the screw down so that the connector will not pull loose. Do the same to the other. Next, take the loose clothesline wire end that is connected to the braided wire and pass it through one end of one of the dowel rods and wrap around the dowel and a couple of turns around itself so it will not pull back out of the dowel.

Before attaching the other element, place an accurate SWR meter in the antenna line to check the match. Thread a length of the 550 Paracord cord through each of the dowel insulators. Now thread the other clothesline (the one connected to the center conductor of the coaxial wire) through the dowel about 4-6" and make an L-shaped bend so it won't pull out of the dowel. Set the SWR meter to check your match according to the meter's instructions. If the match is too high, then take a pair of wire cutters, and trim the end back just 1/4" at a time until you get the lowest [reading] match you can possibly achieve.

Important note: Care must be taken when trimming the antenna, because you can't put the cut pieces back! Once you have the best match you can get, finish off the end of the wire the same as the first. Now stretch it up between two sturdy objects, and try it out. I have been able to get the same range as a commercial one with mine.

JWR Adds: Some provisos: Be sure to waterproof all connections with RTV silicone, or something similar. Be sure to have an antenna connected whenever transmitting, to prevent damage to your transceiver. Since nearly all CB radio transceivers are set up with vertically polarized antennas, it is important that you rig your antenna vertically. (This way, the geometry of your transmitting wave will match the vertical geometry of the receiving antenna.) This may seem counterintuitive when you are looking at a dipole, but trust me, you should set it up with the two elements running up and down. And, of course, all of the usual antenna safety precautions apply.


Copyright 2005-2012 James Wesley, Rawles - SurvivalBlog.com All Rights Reserved