[TowerTalk] BN-86, and Choke Balun

[Jim Thomson]

Date: Thu, 16 Apr 2020 11:21:56 -0700
From: Michael Tope <W4EF at dellroy.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] RFI, BN-86, and Choke Balun

<In case it is not clear, the BN-86 is not a matching device. It's a 1:1 
<balun, and in my experience they are not very reliable. If it were me, I 
<would replace the BN-86 with a good common-mode choke (one from K9YC's 
<cookbook).

<73, Mike W4EF......

##  The  BN-86 is a joke. Its  a  voltage  type  balun.   I  turned  3 of  em  into  charcoal  years  ago.  The  coatings  on  the  magnet  wire 
burnt  right  off...with  just 1900w  pep  out....  into  low  swr....  ssb  mode.  Replace  it  with  a real  1:1  CM  choke. 

##  there  is  merit  to  installing an  additional  CM  choke  right  at  the  output of a  linear  amp.   Buddy  had  severe  rfi  on  his  80m  yagi,  dsl  issues,  you  name  it.
No  amount  of  filtering  on  those  devices  worked.  RF  into  the  audio on  6M  setup. M2  has  no  clue  how  to  design  a balun  for a 80m  yagi...nor a 6M  yagi.
In  desperation,  buddy  installed 30  inches  worth  of  type 43  beads,  onto  213-u....right  at the  output  of  both  the  HF  amp..and  also  the  6m  monoband  amp.
Problems  solved...even  with  all  the  dsl,  tv,  etc  filters  removed. The M2  baluns  are  way  out  from  the  tower,  so  until  the  yagis  were  removed,  and baluns
replaced  with  real  ones,   the  stop  gap  quick  fix  was  30-36  inches  worth  of  beads...right  at  back  of  amp.  Since  there  is  no  coax on  the  inboard  side  of
each  bead  choke,  the inductive  reactive  bead  choke  will  still  work.  

##  depending  on  coax  layout,  ie:  sometimes a catenary  line  of  coax  is  used to  route  to  shack,  etc.  RF,  in  the  form  of  direct  radiation,  from  the  ant,
  can  still  be  induced  into  the  coax on  the  inboard side  of  the  ant.   A  2nd  CM  choke will  clean  that  up. 

## Use a clamp  on  RF  ammeter  if  you  really  want  to  know  whats  going  on.    I  use a  MFJ-  854..and  its  an  eye  opener.

Jim   VE7RF