[TowerTalk] RFI, BN-86, and Choke Balun

[john at kk9a.com]

I am not sure how well a BN-86 acts as a choke but assuming that you  
have quality coax and connectors, you may be just hearing noise that  
the antenna is picking up, which is something that it is designed to  
do. Lately it is difficult to avoid RFI from poorly designed  
appliances and bad power pole connections. One easy way to check is to  
listen to the noise while rotating your antenna, looking for signal  
strengthen variation. If you are lucky the noise could be coming from  
your own home.

John KK9A


Brian Rehmer KC4KK wrote

For sometime I have been struggling with noise (S4-7) on HF bands with  
my TH-5DX tribander.  I have ~125 feet of RG-8 routed to a BN-86 at  
the antenna feed.  There are several other feeds that are bundled  
together for 40, 6, and 2 meters in the same run up the tower.  The  
cables route to the tower from my second floor radio room inside my  
house.  So, there are lots of things that can couple to the outside of  
the feeds.  I am considering adding common mode chokes to  
reduce/eliminate the noise.  Alot of the time the noise covers the  
entire 15 M band. I can take a small loop and couple to the feeds at  
base of tower and other spots along the feeds and see the noise and it  
varies with position.  It seem this points to common mode as culprit.   
So, there are lots of things that can couple to the outside of the  
feeds.  I am considering adding common mode chokes to reduce/eliminate  
the noise.

  Question is should I add the choke prior to the BN-86 or replace the  
BN 86.  I expect I may need to add chokes to each of the other lines  
too, but where.  Should I add in the shack too or just exit from the  
house to the tower.  Ugh, it could need both - getting to be alot of  
chokes.
Thanks,
Brian
KC4KK