"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@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Tuesday, December 12, 2017 18:26
To: towertalk@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.
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