Evan,
I have a 46' vertical, ~90' horizontal Inverted L with 97 on ground radials
between 75 and 150' long. The antenna base is some 350' from my shack. I'm
feeding it with LMR400 and RG-213. With a base impedance around 22 Ohms, I
built a 2.25:1 UNUN and got an "acceptable" match. I have worked 173 countries
on topband with various antennas, the last 60 or so using this antenna for two
years.
The SWR plot always showed some weird impedances and I was never fully
satisfied with the strange load settings on my amplifier. A week ago I removed
the UNUN and replaced it with a simple shunt coil. My SWR is now 1.2:1 at the
base and 1:1 back in the shack on 1830 kHz. It was nice to load the amplifer
normally and get 1 kW output with only 3 W reflected! The 2:1 SWR bandwidth in
the shack is 60 kHz.
The coil was measured at about 2.7 uH and is wound from #12 AWG bare solid
copper wire, 3" in diameter. I added a couple extra turns so I could use an
adjustable tap to get the best match. I wound 8 turns, each spaced about 1/2".
The tap to ground ended up being 6-1/4 turns from the antenna end.
I have pictures if you would like to see them. Email me at n2cu@roadrunner.com
73,
Tom N2CU <><
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