Common mode chokes, a.k.a. line isolators are 1:1 ununs. If you are using
50 beads or baluns at your antennas you probably don't need line isolators
(at those locations). line isolators are usually used to control errant RF
so it stays out of the shack and out of the audio freq. circuitry when you
transmit (the dreaded RF in your transmit audio). It's usually a problem
if you have your antenna close to your transmitter (for example if you are
on a small lot) or due to the way your gear is grounded, you have rf
travelling on loops between for example, your exciter and amp (via the coax
shield between the two), and back from amp to exciter via your common ground
bus. Most hams put feedline isolators between exciters, amps and
transmatches to break up these loops. They may also put them out in the
line near the antenna to attenuate RF coming back from that point on the
external surface of the feedline shield. if you don't have problems with rf
in the shack (distorted audio, stuff such as your mic biting you when you
grab it & transmit) then you are probably okay without them.
Rob Atkinson
K5UJ
k5uj@hotmail.com
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Question in regard to Common-mode chokes.
I use Force 12 B-1 baluns on 10-40M. On 80 and 160M I use 50 of the small
beads on RG141.
All the Buryflex and hardline is tied together and buried a few inches in
sand for about 125'. It all ends at Ice 303 lightning arrestors (302
arrestor for 2M) on a grounded aluminum panel in my basement. In addition
there is an ICE coax switch, low pass filter for HF and a 2M bandpass filter
on the panel. My amp is tied into this panel. I have one coax line for HF
and one coax line for 2M coming to the room right above it to my rig.
Should I be using Common-mode chokes anywhere? What benefit would they buy
me? Where would I put them?
Tnx for any feedback
Tony
N2TK
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