Switching supplies came up as a topic on the CQ-Contest reflector a few
months ago. I posted the following message there and here it is for the
TenTec list...
Oh, as an update, I used the Astron SS-30M with the TS-850S (mentioned
below) during the Collegiate QSO Party a few weeks back. No hash heard.
- NN6O
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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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