QST did a review of several switching power supplies in the January 2000 issue.
The SS-30M had the "cleanest" DC trace with less than 20mVpp ripple and no
detectable switching spikes while the Samlex 1223 showed less than 30mVpp
ripple but 600mVpp switching spikes. Broadband noise is also 10 to 25db higher
on the Samlex supply. Surprisingly enough, the MFJ unit looks like it has the
lowest spectral noise of all the supplies tested! Spectral plots and trace
displays are in the report. You can download it from the ARRL site in the
members-only section. It's about 670K in size because it includes other
product reviews.
I've confirmed on my TS-850S/AT that you can hear the switching noise. At
Field Day 2001, we used a couple of Samlex 1223 supplies and my '850 would pick
up a 3 S-unit "bump" in the noise floor every few dozen kHertz on most HF
bands. The noise completely disappeared when we turned off the switchers and
used battery power. Although my '850 heard the noise, we weren't able to
detect it on 6 or 2 meters with a TM-255A 2M radio (with TenTec 1209
transverter for 6M). Nor was the noise discernable on Oak Hills or NorCal QRP
HF rigs (the '850 is known to have a VERY sensitive receiver!). I recently
purchased a Astron SS-30M, but haven't had time to test it yet with the same
'850. If anyone's interested, I'll hook it up sometime soon at home and post
results.
73,
- Aaron Hsu, NN6O (ex-KD6DAE)
{nn6o}@arrl.net
{athsu}@unistudios.com
No-QRO Int'l #1,000,006
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