[TowerTalk] Feedline (choke) question

[Brian Beezley]

"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, I believe grounding a coax shield often can keep unwanted shield 
current from reaching a rig, whether the rig is grounded or not. So will 
a series shield impedance in the form of a choke.

I've always thought of ground as a current sink. A good RF ground 
exhibits low impedance, a poor one higher impedance. This does not 
extend to "grounds" away from the surface of the earth. "Grounding" 
something up on a tower may be effective at DC but not at RF.

I can't give a reasoned explanation for my thinking this way. Because 
it's pretty fundamental, I'm open to, and invite, counterarguments. I'd 
be happy to learn that I'm overlooking something. The only problem is my 
current lack of time to participate in an extended discussion. Too many 
pressing projects!

Brian