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

[Michael Tope]

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......

On 4/16/2020 10:17 AM, Jim Brown wrote:
> On 4/16/2020 5:20 AM, Brian Rehmer via TowerTalk 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.  A lot 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.
>
> That could be a good thing, but you may also need to chase down and 
> kill the source(s) of the noise. http://k9yc.com/KillingReceiveNoise.pdf
>>
>>   Question is should I add the choke prior to the BN-86 or replace 
>> the BN 86. 
>
> The choke should ALWAYS be placed between the antenna designer's 
> matching device and the coax, and it should always be right at where 
> the coax connects to it, NOT further down the feedline.
>
>  I expect I may need to add chokes to each of the other lines too, but 
> where.
>
> Where they connect to the antennas.
>
>  Should I add in the shack too
>
> No
> or just exit from the house to the tower.
>
> No
>
> Study k9yc.com/RFI-Ham.pdf  and
> http://k9yc.com/2018Cookbook.pdf
>
> The other thing worth noting is that, at this low point in the sunspot 
> cycle, propagation on 15M and above is pretty stinko, and is likely to 
> remain so for a couple of years.
>
> 73, Jim K9YC
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