[TowerTalk] Common Mode Choke Locations

[David Gilbert]

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 at 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
>