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Re: [TowerTalk] Feedline (choke) question

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Feedline (choke) question
From: David Gilbert <ab7echo@gmail.com>
Date: Sat, 27 Sep 2025 09:11:35 -0700
List-post: <mailto:towertalk@contesting.com>


Except that "ground" isn't actually some sort of sink for RF. Imagine a portable battery operated setup with a dipole antenna and nothing about the rig connected to ground.  A common mode choke will do its job ... a connection from the coax shield to ground doesn't do a thing.

Dave   AB7E


On 9/27/2025 12:31 AM, Brian Beezley wrote:
"This one bothers me. Remember that there really is no such thing as ground for RF - that ground rod is strictly for lightning / static currents. Connecting the shield to a “grounding point” will simply combine the inner and outer currents. That’s really not what we want to do. You need instead to choke off the RF current on the outside of the shield."


Jack, I do not assume that a ground connection has 0 ohms RF impedance. All I was looking for was a low impedance to shunt off most of the coax shield current. Shield current splits at a junction. If the impedance looking toward the ground point is lower than that looking toward the shack, it will carry most of the current. If it is much lower, it should keep nearly all of it out of the shack.

Brian
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