[TowerTalk] Common Mode Choke Locations

[Art Greenberg]

I seek a better understanding of the proper application of common mode 
chokes.

First, the setup:

I have several coax-fed antennas on a crank-up tower. The coax shields 
are bonded to the tower at the top of the tower (at the end of the rotor 
loop) and near the bottom of the tower. The bottom of the tower is in 
turn bonded to a fairly extensive lightning ground system. The coax 
leaves the lower bonding point and is bundled with rotor and control 
cables, all of which go under ground in conduit to an entrance panel 
where the coax encounters lightning arrestors mounted on a copper plate. 
There are also lightning arrestors for the rotor and control cables 
mounted on the copper plate. There is also a copper strap that runs 
alongside the conduit to bond the tower to the copper plate. The copper 
plate is bonded to additional ground below it which is also connected to 
the mains ground.

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

-- 
Art Greenberg
WA2LLN
art at artg.tv