[TowerTalk] common mode chokes, baluns and multiband, doublets

David Robbins k1ttt at verizon.net
Tue Dec 12 15:32:42 EST 2017

"The inductance of a coil of coax is in series with the rest of the transmission line, and if that line looks capacitive (by virtue of its length), the coil of coax DOES NOT WORK to provide isolation. Indeed, it increases common mode current on the line rather than reducing it."

This statement I would debate.... mainly the 'by virtue of its length' statement... that starts mixing the lumped component (coil) with a transmission line model.  In order to properly analyze it you must include the rest of the environment, the distributed capacitance to the surroundings from the shield, the distributed inductance of the shield, losses or pickup from it coupling to stuff around it, and locations of connections to the shield from connections to antenna booms, towers, lightning grounding, etc.  

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Brown
Sent: Tuesday, December 12, 2017 18:26
To: towertalk at contesting.com
Subject: Re: [TowerTalk] common mode chokes, baluns and multiband, doublets

Effective common mode chokes work as a result of a high value of RESISTANCE that is inductively coupled from a lossy ferrite core. 
Resistance cannot be cancelled, so it always reduces the common mode current. You can find a thorough discussion of these principles in k9yc.com/RFI-Ham.pdf  and in the ARRL Handbook.

73, Jim K9YC

On 12/12/2017 10:02 AM, Chuck Gooden wrote:
> A coil of wire is an inductor with an air core and the principle of of 
> a inductor will still apply.  However an air core inductor will not be 
> as efficient as an inductor with a core depending on the mu of the 
> material used.


TowerTalk mailing list
TowerTalk at contesting.com

More information about the TowerTalk mailing list