[TowerTalk] Feed Point Choke Question

[Jim Thomson]

Date: Sat, 7 Nov 2020 07:22:27 -0700
From: Alan Higbie <alan.higbie at gmail.com>
To: Jeff Blaine <KeepWalking188 at ac0c.com>
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Feed Point Choke Question

<It would be interesting if you could identify and measure some particular RFI (or general noise floor) that
needs to be suppressed - and
(2) then install the best designed choke made from what you have available
and
(3) measure strength of that RFI (or noise floor).

<Later, in the Spring, try another (more theoretically optimal) choke - make
<a similar comparison - and see if you can improve suppression of that RFI
<or general noise floor.

< Alan K0AV

## The idea behind the CM choke is  to minimize CM  current. 
And  CM current is easy to measure on the feedline with a clamp on  RF  ammeter.

##   mark the  coax in  several places  with painters green tape.  Take measurements
at those locations with  XXX  amount of power on  freq  ZZZ.  

##  swap CM  chokes, re-take measurements...and compare results.
You only have 3 x choices.  It stays the same,  gets better, or gets worse.
I use an  MFJ-854   RF current meter.  It will only fit coax up to  RG-213 U  size. 

##  You can also install 2 x identical  CM chokes in series.   Pretty easy to get > 10 k ohms
on the lower bands with that method.   Typ results is a 1-4  S unit  drop in noise level   vs  junk baluns.

Jim   VE7RF