Topband: spark gap construction ideas for 160m tower

[Jim Thomson]

Date: Sun, 6 Oct 2019 19:08:17 -0500
From: Rob Atkinson <ranchorobbo at gmail.com>
To: topband at contesting.com
Subject: Re: Topband: spark gap construction ideas for 160m tower

<There are a number of ways of making a ball gap.  but more important
<is arriving at the correct spacing for the gap.
<The way rain is handled is usually by positioning the balls one above
<the other so a water bridge doesn't form between the balls.

<Read this by Mark Persons:
https://www.radioworld.com/tech-and-gear/understanding-arc-gaps-for-am-systems
<Here's another treatment:
https://www.thebdr.net/articles/steel/twrs/LimitingStatic.pdf
<Kintronic sells them
https://www.kintronic.com/shop/tower-ball-gap/

<73
<Rob
<K5UJ

##  a  simple  1 megohm  resistor  across  the  base  will  drain  static buildup.
A  35-100 uh  coil  across  the  base  will  also  drain static  buildup.
Neither  of  the  above  will  work  with  a direct  lightning hit  to  top of
tower.   A  buddy used a helical hairpin   across  the  base of  his   100  ft
tall   160m   vertical....  suspended  between  2  trees...with  T  loading capacity hats.
Helical  hairpin  also  DC  grounds  the  vert. 

##  I  built a simple adjustable  spark  gap  like  Mark  Persons describes 
in  the  1st url  above.   I used  .25-20  brass  machine  screws...and  
also mating  brass  lock  nuts...and  also  brass  acorn nuts..with  their
domed  heads.   IF the  acorn  nuts  get  fried,  replaced real  easy.   

##  My  hb  spark  gap  is  not  for a vertical  though.  Its  wired  across
a  4 H Dahl,  127  lb  choke...  that  I  picked  up across  town.   Its
a  C-L-C  filter  network for a B+  supply.   The C-L-C network  is  in
series  with  the  B+...  after  the  FWB  assy.   The  choke  itself is isolated 
from  the  chassis.   The  spark  gap  is  just a safety precaution....  and  gapped
for  like  300  volts. 

##  Identical  adjustable  spark  gaps  are  wired across the  vac  load  caps
on  the hb linear amps.   Gapped  for a breakdown  thats   way less  than  the 
hi  pot  test  rating  of  the  vac  load  cap.   But  higher than a  max 2.5:1  swr  across
the  vac  load  cap... which  is a PI  net..so  at a 50  ohm  point.   Amps kick  offline
with a 2:1  swr. 

##  Place  a plastic  cover  above  any  outdoor spark  gap.   Any  bugs  will  be  fried. 

Jim   VE7RF