Thursday, October 9, 2014

Simple Ham Radio Antennas: Building a multi-band HF Dipole Antenna. Post #312.


Do you want an efficient multi-band HF antenna that occupies a small space and requires the minimum of construction and maintenance? Then, this video from Larry, the "Radio Ham Guy" is for you. Most of the materials will be found in your ham shack, garage storage room, or at the nearest home improvement or hardware store. This version of the popular "fan dipole" requires only one 50 ohm coaxial cable feed line, a center coax connector, a few end insulators, a tall support and a few tie off points above ground to work. Using the familiar dipole formula (468/f(MHz)=L(ft), you cut separate dipoles for each band of use, connect them to a common center connector, and "fan out" the various elements to nearby support masts, trees, or any other tall object. With careful trimming (beginning with the lowest frequency band of your choice), you can probably get a low SWR for each amateur radio band you chose. I always use an antenna transmatch (i.e. "tuner") as part of the antenna system, just to get the best match possible. It is possible to use the 40 meter dipole on 15 meters if you cut the 40 meter segments to the lower portion of the band. This will make the antenna work as a third harmonic in the phone portion of the 15 meter band. When in doubt, just make a separate 15 meter dipole, attach it to the common center connector, and "fan out" the dipole elements like the other dipoles. This antenna doesn't require a ground plane and will give you years of good service. To reduce the chance of stray rf getting into your shack, you can insert a 1:1 balun just below the dipole center connector. Or, you can "roll your own" rf choke out of a few feet of your feed line. Larry's video is clear, concise, and well-presented. Antenna building is one of the few pursuits amateur radio operators can do that doesn't require a lot of cash or time. Wire antennas can work just as well as commercial products. For the latest Amateur Radio News and Events, please check out the blog sidebars. These news feeds are updated daily. You can follow our blog community with a free e-mail subscription or by tapping into the blog RSS feed.Aloha es 73 de Russ (KH6JRM).