[TowerTalk] 160 vertical question (Top Hat)

[Jim Thomson]

Date: Sat, 3 Feb 2018 20:59:49 -0800
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at 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