I've been spending the winter on 160 meters with my Cushcraft MA160V top-loaded vertical antenna. This antenna has been surprisingly effective for such a short (approx. 36 feet) vertical. I have a decent, though by no means exceptional, ground system. The usable bandwidth is on the order of 20 KHz, and I carefully tuned it for a center frequency of 1820 KHz, positioning me for CW DX fun on Top Band.
Since I obtained the P3 last Fall, I've noticed that I can see the rolloff characteristics of my antenna simply by looking at the display with band noise. We had considerable freezing rain and sleet, followed by snow here in St. Louis in the past couple of days. The top loading elements (coil and top-hat capacitance) have a thick coating of ice on them. The other night, I turned on my K3 and P3 and was prepared for listening for DX at sunset when I noticed the P3 was indicating a frequency response rolloff far below what was normal. In fact my antenna had made a QSY right out of the band to a new center frequency of roughly 1770 KHz! Even at the 1800 KHz band edge my SWR was about 5.5:1. Having used this and other top-loaded verticals, I had experienced shifts of 15-20 KHz due to icy conditions previously. But never a 50 KHz shift! I tried using my MFJ-259B Antenna Analyzer to check the resonant frequency and bandwidth of my antenna, only to discover the lower limit of the analyzer is 1800 KHz. Now, I'm waiting for some of the ice to melt or evaporate from my antenna so I can use it again. So I'm watching band noise on my P3, waiting for the resonant frequency to come back up. Already today, it has moved up about 10 KHz (even though the temperature remains below freezing). I just thought I'd point out this aspect of the P3 (or other panadaptor frequency displays) for indicating the frequency response characteristics of high-Q antennas. 73, Chuck Guenther NI0C ______________________________________________________________ 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
