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[TowerTalk] Ferrite choke thermal situation

To: towertalk reflector <>
Subject: [TowerTalk] Ferrite choke thermal situation
From: Dan Hearn <>
Date: Sat, 14 Apr 2012 18:18:34 -0700
List-post: <">>
We all owe a debt of gratitude to K9YC for all of the work he has done and
provided to us on many topics as well as ferrite chokes.
  He did an excellent  analysis of the heat problem in line chokes in one
of his PDF's . He assumed a worst case condition as I understand it and
various operating modes.
Page 28
  Re the Balun Designs chokes I am only concerned with the coax jobs. They
seem to use the W1JR design on the 2.4 cores with the crossover for half of
the turns. I have built and measured a number of them. I also measured them
at 50mhz and they are quite effective there..
  It seems to me that you have 2 choices. Either you use large coax like
213 and a number of cores in the open or you use fewer cores with more
turns of Teflon coax in which case you put it in a box with connectors.
  I believe that the current thru the choke is dependent on the mismatch at
the antenna, unbalanced  coupling between the coax below the choke to the
antenna or surrounding objects, and the length of the coax line to base
ground. In a well designed station the current through the choke is not a
serious problem.
Dan Hearn

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