RF Quiet Wall warts

Jeff Liebermann <jeffl@cruzio.com> wrote:
> I do some computah work for the author.  I recently unloaded about 50
> lbs of linear wall warts on his doorstep.  Over the years, he has
> systematically replaced as many switchers with linear power supplies
> as possible.

Swiching power supplies are much more efficient, both in operation
and in manufacturing.  They use a lot less resources to manufacture.

That is what the world needs more than clean HF bands.  Live with it.

"whit3rd" <whit3rd@gmail.com> wrote in message 
news:d4b7dc6f-231a-45ed-a704-614bf10e08aa@googlegroups.com...
>> FWIW, ferrites rarely do more than 3-6dB of attenuation.  A long stack of
>> them, maybe over 10dB.  The reason is, if there's no shunting impedance 
>> (to
>> ground, or, more generally, to the other cable coming out of the box), 
>> it's
>> an impedance divider against the capacitance-to-space of the cables in
>> question.
>
> I've seen more dramatic results than that, with the common-mode ferrite 
> formulations
> which are very lossy (it's a series resistor at RF).

Then you probably had one of those lucky situations where there was shunting 
impedance to ground. :-)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On 08/26/2017 02:36 PM, Rob wrote:
> Jeff Liebermann <jeffl@cruzio.com> wrote:
>> I do some computah work for the author.  I recently unloaded about 50
>> lbs of linear wall warts on his doorstep.  Over the years, he has
>> systematically replaced as many switchers with linear power supplies
>> as possible.
> 
> Swiching power supplies are much more efficient, both in operation
> and in manufacturing.  They use a lot less resources to manufacture.
> 
> That is what the world needs more than clean HF bands.  Live with it.
> 

Gee, it's great that there are people like you, People Who Know Best. 
Otherwise we the great unwashed would have no one to tell us how to 
think, and then where would we be?

There's nothing that prevents one from making quiet switching supplies. 
They just cost more.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

On 26 Aug 2017 18:36:58 GMT, Rob <nomail@example.com> wrote:

>Jeff Liebermann <jeffl@cruzio.com> wrote:
>> I do some computah work for the author.  I recently unloaded about 50
>> lbs of linear wall warts on his doorstep.  Over the years, he has
>> systematically replaced as many switchers with linear power supplies
>> as possible.

>Swiching power supplies are much more efficient, both in operation
>and in manufacturing.  They use a lot less resources to manufacture.
>
>That is what the world needs more than clean HF bands.  Live with it.

It's not just the HF bands.  A few years ago, we were helping the
county radio shop track down a noise source that was trashing the
input to one of their VHF voting system receivers.  It turned out to
be a switching power supply running some LED lighting about 1.5 miles
away.  Something like these:
<http://www.ebay.com/itm/Power-Transformer-Supply-ACDC-12V-5A-10A-15A-20A-30A-Switching-Strip-Light-Drive-/272786549536>
Someone tore it apart and determined that there was little in the way
of RFI protection on either the input or output.  However, that wasn't
the real problem.  The PWM chip had a feature called "spread spectrum"
where the RFI generated is spread over a much wider bandwidth,
resulting in reduced peak power.  In effect, it takes some fairly
narrow band radiated switching junk and splatters it all over a wider
bandwidth.  The FCC allows this because some brilliant attorney
decided that only the peak emission level was important, not the
overall power belched by the interference source.  So, you're right...
the world needs more than clean HF bands.  It needs a non-political
FCC.

About 30 years ago, a few people saw what was coming and tried to
convince the FCC and the ITU to allocate specific frequencies for
switching power supplies.  Such a frequency would be declared the
dumping ground for switcher RFI, such as 13.56MHz.  We worked out a
preliminary frequency plan, which was far from ideal, but at least a
good start.  The idea was summarily killed when the spread spectrum
trick was accepted by the FCC as the "solution" to the EMI/RFI
problem.

So, while you're enjoying your switcher powered gizmos and gadgets,
there are a few of us that are doing what we can to clean up the mess
that your attitude seem to have left behind.


-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Steve Wilson wrote:

> I guess the old guys have died off, and
> amateur radio doesn't have the same appeal as google.

It has never been very appealing, in my wannabe HAM days they
mostly exchanged RST reports. Several days of listening to the
real HAMs entirely killed the desire to obtain my own license.
I wanted to build devices, not to become a protein-based RSSI.

> Electronics seems to be following the same route as the vacuum tube. But
> there are very active local clubs into Arduinos and robotics, so there is
> some hope for the future.

But they moved from designing electronics to connecting modules. 
Sometimes the results are very spectacular, but, on the other hand, no 
ready-made
module == impossible. Still much better that listening to Bieber, though...
	
	Best regards, Piotr

Rob wrote:

> This is also the reason why nobody cares about the interference from
> wall warts.  The AM (HF) bands are no longer used by the public.

Germany and a fair fraction of Europe work thanks to the AM
transmissions (DCF77@77.5kHz for time broadcast, DCF49@129kHz
for remote control of power meters etc.). Unfortunately, the
lower LF band is where the EMI is highest. There are PM signals
too, but no consumer-grade devices use that due to the involved 
complexity. There is also LORAN, but it is not very useful on land.

	Best regards, Piotr

Jeff Liebermann wrote:

> About 30 years ago, a few people saw what was coming and tried to
> convince the FCC and the ITU to allocate specific frequencies for
> switching power supplies.  Such a frequency would be declared the
> dumping ground for switcher RFI, such as 13.56MHz.  We worked out a
> preliminary frequency plan, which was far from ideal, but at least a
> good start.  The idea was summarily killed when the spread spectrum
> trick was accepted by the FCC as the "solution" to the EMI/RFI
> problem.

But would it ever work? The frequency of the switchers is mostly limited
by the magnetics and then by the MOSFET drivers/losses. That puts them 
in the 50kHz...1MHz band, which is/used to be densely populated. They
use square waves of variable duty cycle, with the harmonic garbage way
above their "baseband". The resonant soft switchers are a novelty from
the mass market perspective. So how would a static allocation of, say,
100kHz help here?

	Best regards, Piotr

On Sat, 26 Aug 2017 12:54:12 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On 26 Aug 2017 18:36:58 GMT, Rob <nomail@example.com> wrote:
>
>>Jeff Liebermann <jeffl@cruzio.com> wrote:
>>> I do some computah work for the author.  I recently unloaded about 50
>>> lbs of linear wall warts on his doorstep.  Over the years, he has
>>> systematically replaced as many switchers with linear power supplies
>>> as possible.
>
>>Swiching power supplies are much more efficient, both in operation
>>and in manufacturing.  They use a lot less resources to manufacture.
>>
>>That is what the world needs more than clean HF bands.  Live with it.
>
>It's not just the HF bands.  A few years ago, we were helping the
>county radio shop track down a noise source that was trashing the
>input to one of their VHF voting system receivers.  It turned out to
>be a switching power supply running some LED lighting about 1.5 miles
>away.  Something like these:

Over a mile away?  Did you sic the FCC on them?  Good point, though,
they should ban all those new fangled fluorescent and LED lights and
go back to good old tungsten.

><http://www.ebay.com/itm/Power-Transformer-Supply-ACDC-12V-5A-10A-15A-20A-30A-Switching-Strip-Light-Drive-/272786549536>
>Someone tore it apart and determined that there was little in the way
>of RFI protection on either the input or output.  However, that wasn't
>the real problem.  The PWM chip had a feature called "spread spectrum"
>where the RFI generated is spread over a much wider bandwidth,
>resulting in reduced peak power.  In effect, it takes some fairly
>narrow band radiated switching junk and splatters it all over a wider
>bandwidth.  The FCC allows this because some brilliant attorney
>decided that only the peak emission level was important, not the
>overall power belched by the interference source.  So, you're right...
>the world needs more than clean HF bands.  It needs a non-political
>FCC.

Nonsense.  Receivers are sensitive to the in-band energy.  Spreading
it out *helps* EMI.  It has other issues but it does do exactly what
it was intended to do.  BTW, EMI tests aren't just peak tests.  The
unit has to test quasi-peak and average masks, as well.

>About 30 years ago, a few people saw what was coming and tried to
>convince the FCC and the ITU to allocate specific frequencies for
>switching power supplies.  Such a frequency would be declared the
>dumping ground for switcher RFI, such as 13.56MHz.  We worked out a
>preliminary frequency plan, which was far from ideal, but at least a
>good start.  The idea was summarily killed when the spread spectrum
>trick was accepted by the FCC as the "solution" to the EMI/RFI
>problem.

Which would do absolutely nothing for harmonics (the real problem)
unless all of the harmonics of your magic switching frequency were
also reserved.  13.56MHz would be rather useless as a reserved
switcher frequency, considering that this is rather high for the
fundamental (see above for harmonics).  

The issue is proper design.  It can be, and is, done.  Some industries
have stricter limits than the FCC's and they deal with switching power
supplies without too much trouble.
>
>So, while you're enjoying your switcher powered gizmos and gadgets,
>there are a few of us that are doing what we can to clean up the mess
>that your attitude seem to have left behind.

Not too self-important.  No, not you!

On Friday, August 25, 2017 at 5:39:21 PM UTC-4, Tim Williams wrote:
> "George Herold" <gherold@teachspin.com> wrote in message 
> news:93599ccd-3251-4d04-93c4-a140ac54523d@googlegroups.com...
> > That makes sense. I do a lot of hunt and pecking when dealing with
> > interference.  Here's my fav, ferrite choking a usb line.
> >
> > https://www.dropbox.com/s/twhtnr6mzq7mwil/ferrite.JPG?dl=0
> >
> > It worked and I moved on.  :^)
> 
> The irony is, see that shielded connector and cable?  This is something that 
> should be literally impossible to happen.
Oh, I assumed the common mode got in at the source.  The computer 
ground (or something) was bouncing around.

George H. 
> 
> I wonder if there's actually a "Typhoid Mary" among appnotes where the 
> connector housing is shown with a ferrite bead to ground.  USB connector 
> appnotes are uniformly bad.
> 
> Tim
> 
> -- 
> Seven Transistor Labs, LLC
> Electrical Engineering Consultation and Contract Design
> Website: http://seventransistorlabs.com

On Sat, 26 Aug 2017 23:27:55 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>Jeff Liebermann wrote:
>
>> About 30 years ago, a few people saw what was coming and tried to
>> convince the FCC and the ITU to allocate specific frequencies for
>> switching power supplies.  Such a frequency would be declared the
>> dumping ground for switcher RFI, such as 13.56MHz.  We worked out a
>> preliminary frequency plan, which was far from ideal, but at least a
>> good start.  The idea was summarily killed when the spread spectrum
>> trick was accepted by the FCC as the "solution" to the EMI/RFI
>> problem.

>But would it ever work? The frequency of the switchers is mostly limited
>by the magnetics and then by the MOSFET drivers/losses. That puts them 
>in the 50kHz...1MHz band, which is/used to be densely populated. They
>use square waves of variable duty cycle, with the harmonic garbage way
>above their "baseband". The resonant soft switchers are a novelty from
>the mass market perspective. So how would a static allocation of, say,
>100kHz help here?
>
>	Best regards, Piotr

I'm fairly sure the scheme would work if the switchers were frequency
stabilized with either a crystal oscillator or ceramic resonator. Same
as with any uP or clocked device.  Most of the energy would be in the
fundamental and 3rd harmonic.  As the harmonic frequency increases, it
becomes easier to shield and filter.

Square waves have 67% of the energy in the fundamental, and the
remaining 33% in odd order harmonics.  As the duty cycle changes the
waveform become asymmetrical, producing more and more even order
harmonics.  Eventually, for really low duty cycles, it becomes a pulse
train which produces a comb line of equal power signals.  
<http://www.analog.com/en/analog-dialogue/articles/understanding-switching-reg-output-artifacts.html>

Obviously, we're not suggesting that all switchers operate at
13.56MHz, which incidentally was one of the original diathermy
frequencies.
<https://en.wikipedia.org/wiki/Diathermy#Short_wave>
There are other frequencies, but none low enough to be usable in a
switching power supply:
<https://en.wikipedia.org/wiki/ISM_band>
So, we had to find an empty frequency and go through the ordeal
process of getting the FCC, ETSI, CEPT, and later the ITU to allocate
or reassign new frequencies.  At the time (about 1977) it was apparent
that the long wave marine navigation beacon band (160KHz to 530KHz)
was eventually going to be replaced by NAVSTAR (now known as GPS)
system.  Since it was expected to take at least 20 years to get
approval for a reallocation of the LW spectrum, this was a reasonable
strategy.  As it turned out, most of the US beacons were turned off in
1997, almost exactly 20 years later.  There was also a problem with
the US Navy, which wanted some of the low end of the LW beacon band
for submarine communications.  However, none of this happened when
spread spectrum PWM power supply modulation arrived and killed the
plan.



-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558