TopBand: Some antenna help from you...

[Bill Fisher, N4VJ / K4AAA]

I'm cc'ing the list for other opinions and to give some others an idea of
what I'm using and how it works.

Currently I'm using an elevated sloping ground plane.  The feed point is 10'
off the ground and runs to the top of a tower at about 100'.  The feed point
is also about 15' further down the hill (in elevation) from the base of the
tower.  The slope of the wire is probably 35 or 40 degrees.  It has 4
elevated radials.  Two of them rise to about 50' off the ground at the ends.
One goes back through the big tower that holds up the vertical and the last
one is about 70' off the ground at the end because it runs down the hill and
I put it in a tree with slingshot.  It's almost level with the feed point of
the antenna.

My SWR on this antenna with a 50 ohm feed is best case 1.7:1 at about
1830Khz.  I never ran the noise bridge on it because I'm too lazy to go to
Radio Shack and buy a small RX for doing such things.  Anyway... I had
trouble after installing it with the amplifier tripping off at the low end
of the band or running much more than 1000w out.  I bought a vacuum variable
cap and installed it on Sunday during the ARRL DX contest.  The cap is
installed between ground (radials) and the vertical member.  After
installation the SWR was 1.1:1 at 1905Khz.  Adding 5' of wire to the
vertical only brought the resonant frequency down to about 1880Khz and made
the wire too droopy.  

So I installed several coils of wire around a drain pipe (in the spirit of
the Home Depot special that it is) and cut the coil so that the resonant
frequency was 1830Khz.  Now I have an antenna with 1.1:1 SWR at 1830Khz.  I
only had a short amount of time to check it with the amp.  But I found that
the amp (AL1500 / 8877) didn't seem to want to put more than about 1200w out
even with 100w of drive.  This amp will do significantly more power in to a
dummy load on the same band.  

The antenna seems to work fine even with the higher SWR and low output
(1000w).  We worked only 4 less countries than W4WA and we were only M/S
(not that Ron couldn't kill us on 160 if he wanted to do so).

I wonder if you have any thoughts on this arrangement? 

Thanks

Bill Fisher




Bill Fisher, N4VJ & K4AAA (EX KM9P)
http://www.contesting.com 






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