TopBand: 160m InvL 2 dip SWR

[Joe L Blackwell]

>On the 3830 reflector, Ken, WO1N writes:
>Putting a 160m Inverted L 20' from a 160-40 trap dipole caused 2 SWR
>dips in the InvL.
>
Thinking top band folks would be interested in this, de Joe AA4NN.
Ken is the only person I've heard mention a 2 dip SWR in an InvL .

Working alone, I put up a 3/8 wave InvL using #14 copper, vertical
section
80 ft, horizontal 112 ft.   Dipped at 1.815;  I kept pruning the
horizontal
section and the dip at 1.815 just wouldn't move !!   I accidentally tuned
the MFJ analyzer up the band and got a beautiful dip at 1.925 !!! 
Realizing
what was going on I lowered and grounded the ends of the W9INN 160
dipole and got a "regular" dip.  Added wire to the horizontal section and
got a dip where I wanted it.  However, a somewhat narrow bandwidth.
I hated to lose the dipole, so mulled a 1/4 sloper, but no matter how I
oriented the sloping section, the 2 dip SWR wouldn't go away.  InvL is
about 25 ft from the 160 dipole.

I replaced the vertical section with a 4-wire cage, #14 copper, spaced
five inches apart.  That effort broadened the 2 to 1 SWR to 70 kHz !
I have 37 radials and 3,000 sq ft of chicken wire under the antenna.
Using a Jennings variable capacitor, it took 316pf  to provide the right
amount of capacitive reactance.  316pf is in about 12.5 ft of coax.

The idea of a 3/8 wave puts the maximum current about 60 ft up on
the vertical section, as opposed to a 1/4 wave where current is max
at the base.  The 3/8 InvL really proved itself in the CQ 160 contest.
It's a pretty good listener as well.

73,
Joe  AA4NN



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