On Mon, 28 Jan 2008 11:27:20 -0000,
Richard wrote in
:

I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used for
receivers? TIA.

Some switchers are very good, some aren't very good at all. One friend
has the Icom PS-120 (I think) for his Icom transceiver, and finds it
to be so noisy as to be unusable .Other friends have other switchers
and find them to be OK, and a third group find them somewhat noisy,
but tolerable if you don't mind tuning around the birdies.

I use a Samlex 30-Amp switcher to drive my Yaesu FT-897D in the shack,
and it's just fine above 500 KHz or so. It *does* put out some hash in
the 20-500 KHz region; my SDR-IQ receiver's waterfall display shows it
quite plainly.

You may find a linear-mode supply (xfmr; half-wave, full-wave, or
bridge rectifier; filter) to be better for your use; I don't know of
a lot of 24V switchers. Certainly a linear supply will be quieter if
done well, as the only noise will be from ripple that gets through the
filters, and the tiny bit of hash from the rectifier junctions turning
on and off.

--
I had the largest, strongest tornado ever recorded march by just four
miles away in May of '99, I could feel the house breathing from the
subsonic pressure wave. It's a Live Thing, like Fire.
-- Charly the *******, in rec.org.sca