"...I'm not sure what it's called, but it was some sort of "inverted sloper"
or "reverse ground plane" ..."
See "Simple, Effective Elevated Ground-Plane Antennas" by Tom Russell, June
1994 QST, page 42,(available in the QST archives on the ARRL website) or
page 6-15 in the 20th edition of the ARRL Antenna Book.
73, Ted W4NZ
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of jim Jarvis
Sent: Saturday, January 02, 2010 11:36 AM
To: RLVZ@aol.com; towertalk@contesting.com
Subject: [TowerTalk] 160m antenna
Since I'm coming in late on this, I'll keep it brief.
a) "many old AM Broadcast Towers" did NOT use "slant feed".
in fact, the FCC almost universally required series fed systems,
and where they didn't, a more typical shunt feed system was used.
There MAY have been one or two using some sort of slant system,
in deep history, (KDKA, WLS?) but I've never seen one, nor did
one appear in broadcast literature in the time I was involved in the
industry.
b) A "half sloper" is actually a slant feed system for the tower, whether
you want it to be, or not. Which is why half slopers have such a
varied
and checkered historical review.
c) If it were me, I would put out proper radials on the 90' tower and shunt
feed
the thing, and forget about trying to put wires close to towers.
Unless
you did
a dipole... but both your towers are way too low for 1.8MHz dipoles to
work
except in NVIS mode.
d) The OTHER possibility might be to use both the 60 and 90' towers, to
support
a folded vertical dipole. See the YCCC site for description of this
"U"
shaped
antenna. Depending on how far apart your towers are, there may be
opportunity
to get the high current portion of this system 30' or more in the air,
and
stand it off
from the tower by a useful distance.
e) The final idea is this--there is a system which puts resonant radials
out from a tower,
at a distance down from the TOP of the tower. They are fed from the
center of the coax,
and the tower is connected to the shield.
I'm not sure what it's called, but it was some sort of "inverted sloper"
or "reverse ground plane"
kind of language. Whether it's effective nor not appears to depend
on the yagi on top of the tower, as it
functions as loading.
I've used one of these, in contests, and it appeared to be quite
effective
on deep Asian and PAC paths from
the east coast, as well as into EU. I believe that system used 6
"radials", 10' down from the tower top,
with a 3 element 40m yagi on top.
Analytically, this looks to me like a more symmetrical variant of the
'half
sloper', with the high current
portion at the top.
N2EA
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