Date: Sat, 7 Nov 2020 07:22:27 -0700
From: Alan Higbie <alan.higbie@gmail.com>
To: Jeff Blaine <KeepWalking188@ac0c.com>
Cc: towertalk@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
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