I have posted on this topic here before. You may cringe at such a blanket
statement, but *all* switching mode power supplies generate noise. As users of
extremely sensitive RF receiving equipment, we must be prepared to tolerate at
least a small amount of RFI from these devices. Show me any SMPS of any size
from any manufacturer and give me a good receiver, and I will let you hear the
noise coming out of the supply. It's just a fact of life.
The noise you hear will be greater with unbalanced antenna systems nearer the
SMPS. Operate from a hotel room with a random wire and an SMPS one of these
days and you'll see what I mean.
The advantages of a SMPS are small size and light weight, but the advantages of
a linear power supply are its quiet-- if not nonexistent-- RFI spectrum.
> -----Original Message-----
> From: Paul Christensen, Esq. [mailto:w9ac@arrl.net]
> Sent: Sunday, 09 March 2003 8:18 AM
> To: tentec@contesting.com
> Subject: Re: [TenTec] Radio Shack 25 amp switching supply?
>
>
> > Mine is going back to the store today. If I lived in a
> place where the
> > noise level was always S5 to S8 it would be fine, but it is
> not the case
> > at this QTH. I hear the noise on 20 meters, now, since the band is
> > mostly quiet this morning. Give me back my linear supply.
>
> I generally stay far away from switching power supplies: My main shack
> supply is centered around an Astron RS-35 linear supply and power is
> distributed to many devices via a RigRunner DC distribution
> panel (which
> btw, is a fantastic product).
>
> However, about a year ago, I was looking for a lightweight
> supply that could
> handle my Triton IV at full 100W output power for portable
> operation. I
> sheepishly purchased the Astron SS-25 after reading a QST
> product review of
> a similar Astron SS supply.
> As I recall, there was essentially no measured noise from the
> Astron SS.
>
> The SS-25 is very light in weight, takes up a relatively
> small footprint and
> doesn't even blush when pushed to 25 amps over extended
> periods of time.
> There's a small thermostatically-engaged whisper fan on the
> rear panel that
> produces nearly no audible noise. I absolutely love the
> Astron SS amp.
> However, I still would not consider it for the main station
> where I leave
> the RS-35 linear supply on 24/7. I simply never want to have
> to consider
> whether or not a spur that I'm hearing is being generated by
> the supply.
> It's difficult enough in trying to localize shack noise
> problems without
> having to examine the supply and rule that out as a potential
> noise source.
> But for intermittent and portable operation, I couldn't be
> more pleased with
> the Astron SS.
>
> Also, Ten Tec makes some nice switching supplies and I would
> bet that theirs
> is at least as clean as the Astron. I know in my previous
> dealings with Ten
> Tec, that they have been very sensitive to the user's power supply and
> potential noise generation.
>
> -Paul, W9AC
>
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