Power Supply Question

[Chuck]

I don't know what gear you are planning on running but if
any are receivers then you may be on the verge of experiencing
power supply RFI.

Many switchers have poor filtering. In  the 80's I worked for
a receiver design house. Both the in-house designed switcher
and the commercially purchased units caused no end of problems.
Noise from the supplies would appear in the noise floor of the
receivers, limiting there use under weak signal conditions. The
commercial units had such a high harmonic content it created
birdies from HF, VHF, UHF and up. We had to use feed-thru caps,
filters and other techniques to get rid of the noise and birdies.
By the time we solved the problems, the supply was not much smaller
than the linear. The only two reasons I can remember we stuck
with the switchers was they were designed in, and some customers
had to have the efficiency.

As much as I dislike throwing away power, the advances in switcher
design have not improved sufficiently to convince me to use them in
low noise apps or with receivers. Switchers have their place, but
if given the choice I would use a linear supply any day of the week.

If you really want to hear a racket just put a notebook computer power
supply near a TV on rabbit ears. Or just plug it into the same phase
ac service as the TV uses.

Best wishes

Chuck WD4HXG

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Date:    Sat, 8 Feb 2003 13:30:02 -0800
From:    Fred Wittman <wittfa19 at EARTHLINK.NET>
Subject: Power supply question

OK, dumb question time again...

I've found a 48v/10A switching power supply, in theory, I can divide the =
output to give me the 23.7v and 13.8v needed for various Heathkit =
applications. Is there something I need to know about using a switching =
power supply for these vintage applications (beyond current =
considerations)?  Thanks in advance.

73 - Fred W.  KG6NYK

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