Letter Re: Radio Communication and Antennas

11-01-2011 • survivalblog.com

All radios need an antenna and the type of antenna chosen will determine important performance characteristics. Let us start with a radio most people are familiar with. The citizens band
radio is typically supplied with some form of mobile vertical whip style antenna. This antenna is usually mounted vertically on the vehicle and it radiates radio frequency energy with mostly vertical polarization. Most CB users have vertical antennas so they are most sensitive to similar signals having vertical polarization. If a person using CB radio wanted to make his signal heard by his comrades more and less by people outside his group, he could change his antenna to a horizontally polarized antenna style and have his comrades do the same. There are other tricks to making a radio signal less likely to be intercepted by an unfriendly force. Antennas can be built to have directional characteristics so that the majority of the radio frequency energy is directed toward your comrades but not towards the opposing force. One cheap and user friendly wire beam antenna is named the Moxon beam. The Moxon beam is built to operate on a narrow band of frequencies and it typically doubles your effective radiated power twice and reduces radiation to the rear by a large degree. The Moxon beam antenna also can be set up for vertical or horizontal polarization. A very important feature of the Moxon beam antenna is it's suitability for matching the impedance of the radio transceiver. Most radio transceivers have a 50 ohm nominal impedance and that just means that in order to transfer the most energy to the antenna, you need the connecting cable and the antenna to both have 50 ohm ratings. Coaxial cable is often used to connect the transceiver to the antenna and this cable for low power would typically be RG-58 (available from Radio Shack and many others).