Not to mention that any device CAN be made nearly completely free of
emissions...by building a gaussian surface around it.
Sure, you have to bond every panel to each adjacent panel, but it can be
done. Once this is done, the number of "holes" in the "shell" will
determine how much RF gets to the outside, as does how well the "shell" is
grounded (to a true ground - remember, at RF, power ground <> earth
ground).
There is still the issue of conducted RF, carried on the output leads
and possibly on the input leads. It seems to me that by putting an
RF choke on the input AND output as close to the supply as possible,
you're pretty much giving the RF energy nowhere to go without a its
putting up a serious fight.
That said, I have one of these RS supplies and will try out the RFI
suppression as soon as is practical.
On Mon, 10 Mar 2003 al_lorona@agilent.com wrote:
>
> 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
> >
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
--
Scott Rosenfeld ARS N7JI
541-684-9970 Eugene, OR Land o' much rain
If you find me on the air, I'm probably in my car
ham@w3eax.umd.edu http://w3eax.umd.edu/~ham
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