Date: Thu, 16 Apr 2020 11:21:56 -0700
From: Michael Tope <W4EF@dellroy.com>
To: towertalk@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
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