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Old July 25th 11, 05:11 AM posted to rec.radio.amateur.antenna
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Default Antenna Magic

On Sun, 24 Jul 2011 15:52:08 -0700 (PDT), Gary
wrote:

Other than the obvious (he was mistaken in what he reported to me) any
ideas as to what went wrong?


You forgot to offer burnt offerings to the radio propagation gods.

I don't think he will ask for any more
advice from me.


80 meters at 100 miles is in the range of the NVIS propagation. 25
miles is about the limit for 80m ground wave, and 300 miles is about
where sky wave starts. The problem with NVIS is that it's really
picky about the height of the antenna above the ground. I don't have
very much NVIS experience to offer any guaranteed suggestions on how
to make NVIS work reliably. I assume the kid will be talking to his
father regularly. My limited and unscientific tinkering empirically
determined that the NVIS horizontal antenna wire has to be fairly
close to the ground. A dipole that close to the ground has a fairly
low impedance. See "height above ground" section:
http://www.w0ipl.net/ECom/NVIS/nvis.htm
My guess(tm) is that with the antenna near the ground, most of the RF
goes straight up, which is what you want for NVIS, while an elevated
antenna delivers more RF towards the horizon. There are plenty of web
sites expounding on NVIS antenna and propagation worth reading. Tell
the kid what you think happened, but let him do the research and
tinkering.



--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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