Hi, Scott,
In fact, I made a number of similar modifications to one of the Astron SS-
family (like Paul's) after I got one about six years ago. I was not pleased
with the RFI before the mods but afterward I considered the supply's
performance acceptable, but not excellent.
Al W6LX
> -----Original Message-----
> From: Scott Rosenfeld [N7JI] [mailto:ham@w3eax.umd.edu]
> Sent: Monday, 10 March 2003 1:26 PM
> To: tentec@contesting.com
> Subject: RE: [TenTec] Radio Shack 25 amp switching supply?
>
>
> 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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