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Re: [TowerTalk] Fwd: OCF Dipole Questions

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Fwd: OCF Dipole Questions
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 11 Dec 2016 22:49:35 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Only to the extent that less RF current flows into equipment with Pin One Problems. But that feedline still radiates -- the only thing that changes is the tuner chassis is now hot with RF, and the tuner modifies the current distribution on the line depending on how it's tuned. And none of this changes the fact that off-center-fed antennas are inherently noisy BECAUSE they are imbalanced, nor does it change the fact that it is simply not practical to choke open wire line at the feedpoint.

What COULD block feedline current is a real transformer on a low loss ferrite core, IF the transformer had very low capacitance between windings (because common mode current would couple through interwinding capacitance). This means that windings could NOT lay next to each other as is often done (bifilar, but connected as a transformer), but would have to be on opposite sides of the core. And, of course, to handle power, a beefy, low loss core would be needed. Something like Fair-Rite #67, which N6RK has used for high power transformers.

73, Jim K9YC

On Fri,12/9/2016 3:46 PM, Hans Hammarquist via TowerTalk wrote:
One way to get control over the common mode current is to place a good common mode choke 
between the tuner and the transceiver and let the tuner "float" electrically. 
Don't ground the tuner and leave it far from any grounded equipment. You don't stop the 
contribution from the feeder to the radiated feild but you reduce the RF in the shack 
generated by the common mode current.


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