View Full Version : Mobile 2 meter & 70 cm home brew antennas
04-27-2011, 06:01 AM
I'm going to be installing a TS-2000 in my truck and I'm thinking of mounting 3 antennas on a tool box mounted in the bed of my truck, but I've got a few questions. For 80-6 meter operation I plan on mounting a Little Tarheel II in the center of the tool box. For 2 meter & 70 cm operation (TS-2000 radios have one connection for 2 meter & another for 70cm, hence the separate antennas) I'm thinking of making my own antennas using some extra 3/8x24 mounts I've got. The idea is to weld the vertical radiator to a stainless steel bolt, but I'm unsure if I should use 1/4 wave or 1/2 wave? Heck, could I even go full wave for the 70 cm? Also, might I run into problems with all 3 antennas only having a maximum of 14 inches of separation from each other? I'm thinking it might only be an issue for the 2 meter antenna? Lastly, am I correct using 146 as my center freq for 2 meters & 435 for 70 cm? Thanks for any input.
04-27-2011, 08:47 AM
A tool box mount puts an HF antenna too close to the cab, and also will not provide an effective counterpoise. Although some contacts will be possible, you'll get out better with your HF antenna bonded to as much truck as possible, and back away from the cab. Some research is needed, and this article by K0BG is a good starting point. (http://www.k0bg.com/antmount.html)
Simple 2 meter & 70 cm quarter wave antennas can be made as you've described. The tool box is a good counterpoise for UHF, and probably adequate for VHF. The biggest problem with a tool box mount is its location. You really want those antennas atop the truck, not nestled down next to the metal cab.
A half-wave vertical for either band is not so simple because the feed point would have a very high impedance. Commercial half-waves use a matching device at the feed point. You can build them, but you'll need to crack a book or two first.
A full wave vertical for either band would not be a satisfactory mobile antenna due to a very high angle of radiation (think end fire). You don't want your mobile antenna pattern aimed straight up toward the sky; instead, it should be omnidirectional and flattened out toward the horizon (where the other stations are most likely to be located). Antennas from quarter wave through 5/8ths wave are most effective.
04-28-2011, 04:29 PM
Great, thanks for the help!