Let's call that spectacularly reduced attenuation at low angles.
If you haven't heard it come in driving up to and onto a saltwater
beach with a mobile HF rig/whip, you've missed one of life's great
hamming experiences.
It's like somebody turned on the switch. The difference at those 2-4
degree incoming angles is astonishing.
73, Guy.
----- Original Message -----
From: "jljarvis" <jljarvis@abs.adelphia.net>
To: <towertalk@contesting.com>
Sent: Monday, March 11, 2002 8:59 PM
Subject: [Towertalk] Reflection Gain
With due respect, Yuri....reflection gain exists for
grazing incidence moonbounce signals. There is an
additive behavior here, which recovers part of the
signal which would be below the horizon, but reflect back
up to add into the beam. But this is NOT at HF...it's at VHF/UHF.
It does NOT exist for vertically polarized HF signals over
earth. All you're seeing over seawater is reduced attenuation
from imperfect earth...when you get to highly conductive ocean.
Yes, you're right that highly conductive ground also reduces
IR losses at the drive point.
But at low angles, you do NOT get gain from a good ground plane.
All you get is reduced attenuation. Result is the same...the
process is different.
n2ea
-0-
> Any language suggesting 'seawater gain', or 'reflection gain',
> is imprecise, at best. It IS true that verticals work better over
highly
> conductive earth. But there ain't no gain there.
There IS a gain somewhere between 10 - 15 dB next to, or over salt
water with
vertical antennas as compared to similar antennas installed inland.
Jump in
the mobile and drive around you WILL see it! Even modeling programs
show it.
Numerous factors come into a play with salt water front: better
"ground"
improves efficiency of the antennas, huge "ground plane" brings gain
at very
low angles (Brewster), unobstructed plane horizon and no noise
generators out
there (except sun).
Jim Jarvis
Keithley Instruments
Essex Vermont
802 872 5830 voice
802 872 5831 fax
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