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[TowerTalk] Re: 40M Interference

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Subject: [TowerTalk] Re: 40M Interference
From: (L. B. Cebik)
Date: Wed, 16 Jul 1997 07:08:29 -0400 (EDT)
The world is full of inadequately filtered and/or regulated supplies, like
the old RS in question.  Most, however, have reasonably adequate
transformers and at least semi-decent cases, the two most expensive parts
of a power supply these days.  The regulators, pass transistors,
rectifiers, capacitors, etc. are all cheap.  The handbooks have a good
number of good circuits that can be reproduced for a few bucks.  In the
process, you can RF proof the supply with appropriate AC line, rectifier,
and DC line filtration--inside the case--plus add whatever
metering/indicators you prefer.  So unless you know that the supply has a
bad transformer (not merely one that needs derating), you might make it a
project for a cold winter evening, when the soldering iron heat will help
to warm the shack.

Most supplies that show changes in voltage in the presence of RF have
little or no RF filtering.  You can add filters to the DC lines, inside or
outside the case.  For a temporary fix, running the dc lines through a
ferrite core several times will to the job, but in a bulky way.  Same for
the AC cord.  However, these isolation techniques will not make for poor
regulator/filtration/overload circuitry.



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