[Elecraft] RE: Switching supplies, my experiences...

Wed Apr 3 12:42:01 2002

Hello to all,

Seems like the only subject with more dialog than switching power supplies
is antennas...so, to add to the noise, here's my experience, Rick.  I don't
have a horror story as much as good old diagnosis and remedy.

I first tried an Alinco switching supply with my Icom IC-706MkIIG and then
with the Yaesu FT-817.  This was their 25 amp version with the meter and
auto plug in addition to 5-way binding posts - a nice little compact
heatsinked case, too.  I bought it knowing that birdies might be a problem
depending on the filtering and radiated isloation designed into the unit and
it had a little knob so that I could vary the switching frequency right from
the front panel.  Boy, that should have been a give-away!  I was fortunate
to have a **really** nice HP heavy duty regulated supply as my reference,
too, which I knew worked perfectly.

I got consistent hetrodynes all up and down the bands on both radios (I'm
about half-way through my K2 right now so no comment there).  I know it was
the supply since I could tune around them with that knob on the supply.
Tried all sorts of the normal ways of reducing the interference - grounding
schemes, clip-on torroids, additional inline filtering, etc.  No help and no
significant change in the radio's behavoirs.

So, I sold it back to where I bought it and got an 'analog' power supply, a
35 amp Astron in my case, but the brand is less imprortant than the design
center of an 'old school' regulated supply.  Bigger, runs hotter, less
efficient, you bet, but its also dead quiet.

So, my experience is to stay away from switching supplies unless there's no
other option.  BTW, Radio Shack has a 3 Amp non-switching regulated power
supply with 5 way binding posts and an auto lighter socket for about $40 or
so.  I'm using it with the FT-817 and it, too, is dead quiet - does have a
bit lower regulation, in terms of ripple, than the Astron but that's
quibbling.  At least I've eliminated that point of interference in my setup.

Hope that helps, Rick.

Cheers,

David/KG6IRW

<<< snip >>>>
From: "Rick Shindley" <[email protected]>
To: "elecraft digest" <[email protected]>
Date: Tue, 2 Apr 2002 22:01:51 -0600
Subject: [Elecraft] switching power supplies

Switching power supplies are a noise sources, but very convenient travelling
companions!  If you find a switcher that seems to be "noise free", try
powering it from a variac over the range of possible input line voltages
(and various load currents) to see if it remains quiet over the frequencies
you intend to operate. You could be disappointed!

Switchers have a tough time limiting the noise they introduce common mode
into the power line. Common mode noise is easily converted to differential
mode noise in your receiver by way of high Z "ground" paths and even antenna
selection!  Better to not use a switcher at all in a radio application if it
can be avoided.

For many, they work just fine but there are no guarantees!  It would be
interesting to hear from people for whom the switchers HAVE NOT worked well.
Theory is one thing, the real world is another. Are there horror stories out
there waiting to be told?

Rick KC0OV
K2 1360 (on a linear supply)