[TowerTalk] Which Balun with the TH7DXX

[Jim Thomson]

Date: Sun, 21 Jul 2013 22:30:24 -0400
From: "Anthony W. DePrato" <wa4jqs at mikrotec.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Which Balun with the TH7DXX

>What balun is being used with the TH7DXX.  over the years i have 
>owned a few hy gain ants and burnt up the Hy Gain BA baluns that 
>were offered. so i went to wind your own coax baluns.. i was reading 
>a few of the old articals on tower talk and saw where the TH7DXX 
>would not work well with a coax balun.. my amps are Alpha 3 tubers 
>and Henrys so dont want to have to replace their so called high power BA-4000
  someday in the dead of winter hi hi... what are most of you using . 
thanks for the help
73 Tony


##  Is hygain/mfj still selling that  useless  BN-86 balun ??   I vaporized
3 of em back in the late 1970 s.   Dunno why they would have the 
audacity to still make it. 

##  coiled up coax is not the answer either, the Z is  too low.   Like gerald sez,
the wire leads on the baluns output is part of the total DE ele  length. 
So if using coax... factor that in...and make the Y the correct length. 

##  4 wraps  of  213 U around   4 x 2.4 inch OD    type 31 ferrite will do the trick
for a balun.... but the assy  has to be kept away from the boom.   You don’t want  stray V
from boom to coiled coax.  The  BN-4000 will also work...and uses type 77 beads..which
are no longer made.   They may well have switched to type 43 or type 31. 

##  I remember  opening up several BN-86 baluns... they looked like  the ferrite  had cracked,
or the magnet wire had arced across, between adjacent winding turns.    Nothing wrong with
voltage baluns..provide teflon sleeving is slid over the magnet wire.   There is magnet wire, then there
is magnet wire.  The good stuff is polyimide/kapton..and has  15 kv  insulation.   Then it requires  30 kv
to arc between  adjacent turns.    slide teflon tubing over the 15 kv magnet wire...and u will never get it to arc.

##  These days.. I would not mess with voltage baluns.  A simple, bomb proof  one to one choke balun,
with a high Z  is  easy enough to fabricate  fro 20-10m.   24 inches worth of  type 43 beads slid over 213 U
will also produce excellent results.. plus it can be taped right to the boom. 

Jim   VE7RF