Date: Sat, 3 Feb 2018 20:59:49 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 160 vertical question (Top Hat)
<Another technique that is often used for matching is to make the wires
<much longer than resonant (that is, resonant around the top of the BC
<band), so that the feedpoint Z is 50 +jX ohms (that is, inductive) on
<160M, and tune the capacitance out by adding a capacitor of equal value
<in series. ?? NEC can easily model this.
<73, Jim K9YC
## I helped a buddy with his 100 ft high top loaded 160M GP, with base aprx
8 ft above the grnd and just 4 x radials. 1st matching scheme we used was
just
a helical hairpin, like F12 uses. Worked superb, 1:1 swr. The helical hair
pin
also had the advantage that the 160m vert wire ele was DC grounded at the
base.
But swr BW was not wide, and he wanted it to function above 1900 khz. Helical
hairpin is just a step up L network, just like u see on a f12 40 m yagi, or
80m rotary
dipole. Hairpin coil strapped between hot side and braid of coax.
## next up was a surplus motor driven 4000 pf vac cap. It was configured
like
an L network, with series coil 1st, then the cap wired between right end of
coil..and ground.
It steps up the low Z... up to 50 ohms. That also worked, swr was 1:1
on cw end, but too high above 1900 khz.
## 3rd and last config was to make the T loading LONGER. The 100 ft tall
wire was suspended
by a catenary line between 2 x trees. The T loading consisted of inverted
vee type loading.
Then the 4000 pf cap was simply strapped in series with the base of the ele,
and the cap was
tweaked to 1:1 swr. Swr was essentially flat from 1800-2000 by tweaking
the motor driven
cap from the shack. I believe a small 35 uh coil was strapped between base
of vert to ground, to
dc ground the entire vert.
Jim VE7RF
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