If you got an SWR of 1.2 on 160 meters from an 80 meter inverted L, you
had a lot of loss either in the radial system or in the loading coil.
The resistive part of the feedpoint impedance of that antenna on 160
should be very low, maybe about 4 ohms plus radial system loss. Exact
number depends on antenna details. Sounds like you made a more
efficient coil and the SWR went up, which it should.
Jerry, K4SAV
On 6/6/2015 7:49 AM, Max Cotton wrote:
I have an inverted L antenna resonant on 80m, I decided to add a loading coil
to the base to bring it on frequency for TopBand. I wound a 2.5mm wire coil 16
turns on a bit of square Paxoline board by drilling holes into the board each
side and feeding the coil through the holes, a bit of a struggle but it worked,
not very pretty, it is 146mm diameter and 120mm long 30.5uH. When I first tried
it the SWR after small trimming was 1.2:1 band centre and 2.0:1 band edges. Now
it looked a but ugly, so I decided to neat it up a bit by adding two fibreglass
webs so the coil was now circular and held by a cross section instead of just
the one plane, now when I retried the SWR it is still resonant on 1.800 but
the SWR is now 2.0:1 in the middle of the band and 4.0:1 at the edges the
turns are the same, the inductance is the same but I have lost my fine SWR
curve. I only added the fibreglass and neated up the coil, Ideas what to do
next apart from removing the fibreglass webs and go
in
g back to ugly coil?73 Max M0GHQ
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