I was about to post a suggestion to see K9YC's thorough discussion on feed
line chokes and much more when he posted this. There is a mountain of
information there but to make a long story short, it appears that the best
approach is to use a number of large cores, preferably type 31, operated
above their normal frequency range. This makes a resistive path for unwanted
radiation instead of an inductive one. The inductive mode is inherently
frequency sensitive due to distributed C and not well suited to wide
frequency coverage. I wonder how many of the line chokes using ferrite beads
have been hit with RF from a linear tuned to the wrong band and damaged. I
think Jim is right on target on this subject. Take a look at the line chokes
and baluns being sold by DX Engineering. I looked inside one and found 12
large cores with 2 turns through each of RG142 teflon coax. I believe they
are using the same technology Jim suggests.
My antennas have both the conventional bead chokes supplied by F12 and
some solenoid chokes on plastic pipe. I plan to replace them with the heavy
duty chokes which I will build myself. Cores are available from Mouser and
other suppliers.I am particularly interested in the technology for choking
out radiation from feed line noise pickup into antennas and am still
pondering that.
73, Dan, N5AR
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Jim Brown
Sent: Wednesday, May 14, 2008 3:25 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Tim Duffy's W0IYH Balun-Choke Article (8/2003)
On Wed, 14 May 2008 14:53:49 -0400, Bill Winkis wrote:
>Do we have a better "Mouse Trap in 2008"??
See http://audiosystemsgroup.com/RFI-Ham.pdf
Also see the PPT on Coaxial Chokes at
http://audiosystemsgroup.com/publish
Tim's work is fine for when it was done, but this is a MUCH better
mousetrap.
73,
Jim Brown K9YC
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