I'm tired of putting up with the interference on AM/FM radios that
happen to sit too close to a switched-mode wall wart needed for
another item. Is there any way I can suppress the interference, like
putting ferrite rings on the DC output from the wart, or wrapping it
in aluminium foil, or whatever? If no solution in that direction, how
can I tell if a wall wart I might see on e-bay is switched-mode or the
older transformer type that I assume doesn't create interference?
Looping the output cable several times around a ferrite core or
through a ferrite ring will give some reduction but see later.
probably won't as you couldn't earth it and could be potentially
lethal if the foil or whatever came loose and in contact with the
The switched mode will be a lot lighter so if postage is less it may
give a clue. Most of the Ebay Chinese switched mode offerings are
pretty dire and noise suppression is something which has to be
designed in from the beginning, it can't really be added as an
If you buy from the likes of CPC.co.uk it will cost a bit more but
there is at least some chance the thing will actually meet the various
standards marked on it. On the direct imports CE simply means
"Chinese Export" and they make pretty neat broadband jammers. They
are also amazingly optimistic with current ratings.
No, they are just using American Amps, these are about 3 times
a UK Amp and achieved at unbelievably low temperatures, attached to an
infinite heat sink! Most semiconductors are now always rated in American
Amps because they look better on paper before they self destruct. I used
to rate power semiconductors for reliability in the dim and distant
past. International committee meetings were a hoot!
Decent well designed wall warts should be reasonably well behaved.
Be surprised if they jammed FM except at very close range. AM tends to
be super sensitive to badly designed switched mode PSUs.
You can get clamp on ferrite rings that will stop some of the
interference but buying a better wallwart might be better.
How well they work is another matter. It might take the edge off
something that is borderline but it won't work miracles.
Moving sensitive kit away from the source of interference is probably a
eBay Chinese imports you are lucky if they are electrically safe.
Any modern PSU will likely be switched mode these days (although the
price of iron going through the floor might change that).
Is there a market for old ferrous transformer based wallwarts?
I have seen production Asian switched mode psus, where the CE
marked units had the suppression components removed after approval was
obtained! All the mounting holes were in the PCB with shorting links
inserted where necessary.
I like this 'power supply':
Though note that weight isn't a reliable indicator either:
The wall wart I got boxed with a new Sony DAB/FM portable gave out bad interference on FM, probably they never tested it in a Japanese fringe area. Replaced it with an old heavy iron transformer PSU and no more problems.
Linear external power supplies were effectively killed off by
European Directive ErP (Energy related Products) 2009/125/EC (and
similar American regulations). The related "COMMISSION REGULATION
(EC) No 278/2009 of 6 April 2009 implementing Directive
2005/32/EC of the European Parliament and of the Council with
regard to ecodesign requirements for no-load condition
electric power consumption and average active efficiency of
external power supplies"
This requires external power supplies to have efficiencies and no-load
power ratings which linear supplies cannot meet.
The size of it would normally indicate that and the weight if listed does
But it makes more sense to get proper branded wall warts
that are more likely to have the interference suppressed
properly and get them from amazon where you can send
it back if it produces interference.
You shouldn't be getting interference on FM, give up on AM.
See my post about this, some of use like to tune radios around the short
waves and only powerline adaptors allow for some ham bands by filtering but
most things seem not to bother at all and indeed quite a few routers are
also pretty prone to crap all over the place. Digital and switch mode noise
is relatively easy to contain if its designed in, but sadly this seems to be
a lost art or maybe its penny pinching, I don't know.
This newsgroup posting comes to you directly from...
The long and the short of it is that the spectrum up to around 30Mhz is
now considered pretty much free for all, and is occupied by no end of
devices and indeed interference all operating in those bands.
DSL operates up to several MHz.
SMPSUs in the 100Khz range will propagate muck up to several MHz or more
as will anything arcy or sparky.
It doesn't matter that YOU want to listen to AM radio. No one else does,
so the pressure to enforce is not there.
The best you could probably do is invest in one really good 12v screened
PSU and hang USB sockets off it, and use those to drive equipment.
"The great thing about Glasgow is that if there's a nuclear attack it'll
look exactly the same afterwards."
Oh tell me about it. Ive DESIGNED RF gear, RF gear in close proximity to
PSUS and Shottky TTL.. The TTL was in a tinplate screened can but STILL
the muck leaked out. The final suppression cap had to be soldered
between the PSU pin and the tinplate case. And had to have wires
precisely...so long. An there was still about 3UV of noise on a 75ohm
VHF input, unless you attached a screened cable to it.
The AM noise came from the bridge rectifier. A little too fast to
switch, Again capacitors right across the bridge terminals help. Not on
the circuit board.
Those who want slavery should have the grace to name it by its proper
name. They must face the full meaning of that which they are advocating
I've tried them all plugging it into a suppressed outlet, ferrites earthed
biscuit tins etc, but the main problem is that they are badly designed and
saturate the core on the tiny transformer used to step down the voltage via
a free running oscillator connected directly to the mains via a crude
rectification circuit. I've trawled around many peoples junk and found some
of the old heavy normal type supplies and added conversion plugs on the end
to fit the equipment, No not as efficient much bigger but oh, the bliss at
least until the neighbour starts recharging their laptop or the power line
internet adaptors two doors down are switched on, then its hash gurgle and
buzz from long wave all the way up to over 50 megs in various bands and
wandering burbling carriers and screeching noises from the ticking power
To my mind we should have an electronic equivelent of the noise abatement
society. Short of moving into the middle of a field somewhere I doubt things
will go back now. Too many Chinese imported crap generators. Brian
This newsgroup posting comes to you directly from...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.