The values vary considerably. You will have to experiment. When I used an L
network in New York for this kind of antenna, the L varied from band to band,
and from CW to SSB on 80. I could walk 20 ft and set a rotary switch on the
basement wall next to the feed thru.
Currently the feedpoint of my Inv L for 160 is not at the shack, so using a
tuning network is inconvenient.
I use a 9:1 (3:1 turns ratio) autotransformer wound on a 4 inch x 1 inch
powdered iron core (liberal amounts of pipe thread teflon tape on both core and
3rd winding for insulation), 14 turns to each of the three interlaced windings.
I connect the coax to the first tap, the antenna to the third tap, and the
bottom to ground/radials and coax shield. Run coax to antenna tuner in the
shack. This works on both 80/75 & 40.
Obviously it works all of 3.5-4 MHz band, just change the tuner.
On 80, it has a half sphere pattern, omnidirectional. It works for both DX and
USA. On 40 it acts more or less like the horizontal part of the antenna is a
dipole. The radiation from the vertical part tends to cancel out. The ground is
not critical because of the high impedance feed. Anything that works for 160
will be fine, except in the air radials. Even a plain ground rod will work.
I run 1500 watts on this setup, and the core has never gotten warm. The
impedance after the transformer is low enough that the coax is not carrying wild
fluctuations is current and voltage.
I switch the transformer out with a relay for 160.
"Wireman" sells the core, as do others.
- - . . . . . . - - . . . . - - . . - . .
73, Guy
k2av@contesting.com
Apex, NC, USA
----- Original Message -----
From: Tom Osborne <w7why@harborside.com>
To: TowerTalk <towertalk@contesting.com>
Sent: Friday, October 08, 1999 11:49 PM
Subject: [TowerTalk] 160 ant feeding
Hi TT'ians!
I want to try my 160 inverted "L" on 80. It's 125 (+-) feet long
and I would like to feed it at the base. Does anyone know the
values for an L network I could use for this? Thanks
Tom W7WHY
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