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Re: [TowerTalk] Common Mode Choke Locations

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Common Mode Choke Locations
From: JP <jp@ezoom.net>
Date: Thu, 26 Jan 2023 18:49:23 -0800
List-post: <mailto:towertalk@contesting.com>
Since my current antenna situation is a far cry from ideal (and far from what 
it used to be), I run a common mode choke at the antenna feed point and one at 
the radio end of the coax for exactly that reason. 

J.P. W2XX/7

> On Jan 26, 2023, at 6:29 PM, David Gilbert <ab7echo@gmail.com> wrote:
> 
> 
> I'm not trying to promote choke overkill, but look at it this way. If it is a 
> truly high impedance CMC at the antenna, the shield of the remaining coax run 
> to the shack is essentially a receiving antenna with an open end at the 
> antenna.  If the antenna is a vertical with radials, the coax becomes just 
> another radial.  I don't understand why there wouldn't be additional currents 
> on the coax shield in those cases ... over and above the differential 
> currents the coax is carrying.  If so, depending upon the circumstances, it 
> seems you might want a CMC at the shack end of the coax as well.
> 
> I don't use one there myself, but I've often wondered whether or not I should.
> 
> 73,
> Dave  AB7E
> 
> 
> 
>> On 1/26/2023 5:39 PM, john@kk9a.com wrote:
>> The only location where I use a choke is at the antenna feed point.
>> 
>> John KK9A
>> 
>> 
>> Art Greenberg WA2LLN wrote:
>> 
>> The questions:
>> 
>> I realize that the bonding and lightning ground system isn't an RF
>> ground, but I wonder if it influences the location(s) of common mode chokes?
>> 
>> I -think- a CM choke is appropriate at the antenna feedpoint, despite
>> the bonding setup. Is that true?
>> 
>> Is an additional CM choke appropriate near the bottom of the tower? On
>> which side of the bonding at the bottom of the tower?
>> 
>> Is an additional CM choke appropriate before the lightning arrestor? Or
>> between the lightning arrestor and the equipment?
>> 
>> TNX
>> 
> 
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