On 12/14/2010 8:41 AM, Johnny Siu wrote: > ... > My questions are : > 1. practically speaking, apart from huge traditional wire antenna, are there > any other antennas of managable size (also reasonable efficiency) which can be > easily set up under distress situation?
I built a magnetic loop that covers the range of 160-80 meters. It consists of three turns of 7/8" hard line as the loop conductor and a remotely controlled vacuum variable capacitor for tuning. The antenna is just a tad over six feet in diameter. It can be tuned down to about 1.5 MHz with a 500 pF vacuum variable. With a longer loop conductor (either more turns or larger antenna diameter) and a 1000 pF VVC, such an antenna could get down to the 600 meter band. The instantaneous bandwidth is quite narrow (~2 kHz), suitable for CW and data modes, but not SSB. > 2. to make communciations of say within 200-300km, what ERP is required? I have worked all over North America from Colorado (~2000 mile range) with this antenna running only 100 watts during several contests, and daytime regional coverage is typically out to about 200 miles using 500 watts. The antenna hangs from a tree branch with the bottom of the loop about 8 feet above ground. > 3. for a segment of 15Khz, voice communciation seems quite restrictive. > How > efficent will it be under digital mode (not CW) such as Pactor? The three-turn mag loop typically has a 10-15% transmitting efficiency at the low end of its tuning range if it is built well, and the nulls along the loop axis help in reducing at least one noise source, providing acceptable S+N/N performance on receive. --------------------- Johnny, I can send you a picture of my 160/80m version of this mag loop if you want. Its from an article in preparation for the antenneX on-line magazine. 73, Gus Hansen KB0YH ______________________________________________________________ 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
