Topband: RF choke/balun

[Arthur Delibert]

I think that’s right if the only issue is your own transmit signal bouncing back from the antenna junction and traveling along the exterior of the feedline.  But for receiving, I think a choke at each end of the feedline is important unless you’re in an exceptionally low noise location.  K9YC recommends putting a choke at the antenna end of the feedline, and I’ve found it makes quite a difference in the amount of local noise on the received signal.  If I understand it right, the outside of the feedline picks up the noise signal and carries it to the antenna junction, from where it gets mixed in with the desired signal.

Art Delibert, KB3FJO

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From: Rob Atkinson<mailto:ranchorobbo at gmail.com>
Sent: Friday, September 15, 2017 12:34 PM
To: topband at contesting.com<mailto:topband at contesting.com>
Subject: Topband: RF choke/balun

If you have enough radials at or below ground you won't need a common
mode choke.  You don't say if your inverted L will have an elevated
ground system or not.  If the ground system consists of 60 or more
radials you can probably put a matching network out and the feedpoint
and forget about fooling around with common mode chokes and all that.
The RF current on the exterior of your feed line will be so small it
won't matter.

73

Rob
K5UJ
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