On Wed,3/23/2016 7:12 PM, Wayne Burdick wrote:
I've been using an MFJ-1820T telescoping 20-meter whip for a few months. Considering its length (48"), results have been excellent. I typically use it with the KX3 on a picnic table at 15 W (with an external battery), or hand-held at 3 to 5 W (internal battery).
As Tom Schiller, N6BT, famously noted, EVERYTHING WORKS, sort of. He demonstrated this by working all continents loading a lightbulb that he fed with coax. Tom is the designer of the excellent Force 12 antennas.
I just did a quick NEC model of a 4 ft vertical with loading coil and a single quarter-wave radial laying on the ground, and compared it with a quarter-wave vertical (16.7 ft) with the same single radial. The model is for poor soil, which is typical of most mountainous QTHs. The full-size quarter-wave will be 7.4 dB louder than the shortened one. That's equivalent to reducing a 15W signal to 3W. The difference is slightly greater over better than average ground. The reduced efficiency is due to the greatly reduced radiation resistance of the shortened antenna.
Bottom line -- yes, shortened antennas work, sort of, but full-size antennas work BETTER. If you can afford the weight of a means to support the longer antenna (typically a telescoping fiberglass pole), it's well worth it! And if a shorter antenna MUST be used, LONGER antenna, LESS coil is better.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
