Re: Turn off laser printer with power strip?

Filter on power cord had no purpose because a better filter is
required inside that power supply. What good is removing a glass of
water from a basement when the basement is flooded? A metaphor that is
answered below.

Do not assume a direct (quantitative) relationship exists between
amount of reduced noise and amount of filtering. Amount of noise is a
non-linear relationship. Add filtering (ie only a capacitor) and hear
no noise reduction. Noise has been reduced, but radio volume does not
indicate such reduction. Increase filtering more, and still no
noticeable reduction - even though filtering has been increased. Then
with a little more filtering, noise is substantially reduced. The
relationship looks more like a hysterisis curve. A little more
filtering suddenly causes a massive reduction in noise volume. Noise
volume reduction does not provide quantitative information; only
suggests a subjective trend.

Even a trivial filter inside a power strip was just enough filtering
to cause noise reduction. That does not for one minute say that filter
is effective because a 'glass of water' filter (inside the power strip)
is made irrelevant by an 'electric pump sized' filter that should have
been inside that power supply.

Of course EMI/RFI filtering that John Smith was touting to protect
appliances is totally irrelevant to the original poster's question.
But John Smith touted it as if it was some major improvement - which
the filter is not. Once numbers were applied, power cord filter does
nothing significant - as demonstrated by the filter that was suppose to
be inside your power supply. Purpose of that filter inside a power
strip protector is for a UL1449 requirement - that is also completely
irrelevant to this thread.

Best way to fix your power supply are filters (which provide both
differential and common mode filtering) just for this purpose such as:
http://www.schurterinc.com/products/usa/pemfilter.asp
http://www.corcom.com/
http://www.cor.com/PDF/Q.pdf
http://www.interpower.com/ic/p30-35list.asp

http://www.interpower.com/scripts/wsisa.dll/WService=ic/p35list2.p?only_filter=YES

Meanwhile power supply creates even more noise when connected to an
antenna. What is the antenna for a power supply missing essential
filters? AC electric wires throughout entire house. If your power
supply is that poorly manufactured, noise may even cause interference
with neighbors - which is why that missing filter inside a power supply
is required by FCC regulations (Part 15 if I remember correctly).

Point remains - the fitler inside a power strip protector does
nothing useful. EMI/RFI filtering is not the purpose of that filter.

larry moe 'n curly wrote:
w_tom wrote:
EMI/RFI filtering in power strip protectors is just another example
of junk science.
...
I noticed no reduction in TV and AM radio interference when I used
power strip surge protectors that contained 1 or 3 capacitors in
addition to the MOVs. Only the protectors containing
capacitor-inductor filters helped, and they helped a lot.

If 'filtering' inside a power strip protector causes any noticeable
improvement, then the appliance itself would have insufficient filtering.

But what about my AM radio, which worked off battery?

Particularly appalling is that a cheapo power supply even interfered
with TV. That is massively beyond what is acceptable from any domestic
appliance. Even a simple capacitor would cause significant filtering
because the power supply is so poor - has literally no internal
filtering.

My cheapo PSU had emptyspaces where the EMI/RFI filter components would
normally sit, but when I added just the capacitors (.005 uF between
lines and ground, about 0.22 uF across lines), I noticed no reduction
in interference. The reason I tested first with capacitors alone
because I couldn't find chokes that fit and that didn't seem like
dangerous junk (toroid core wound with vinyl-insulated phone wire).

Filtering inside a power supply must be so good that TV 3
must not be interfered AND even AM radio suffers no interference. So
again, John Smith's power strip filter is not relevant - has no
purpose. But he promotes it on junk science - using numbers he does
not even understand.

If it has no purpose, why did it help so much with my reception? The
AM radio went from totally useless (just a constant buzz/whine/screech)
to about as clear as AM gets, and TV ch. 3 cleared up a lot.

.

Relevant Pages

  • Re: Electrical Interference
    ... During exceptionally strong signals, one would ... cheap power supply for his sound card. ... OP may need buy and connect a line filter that did not come ... with the noise detecting ...
    (sci.electronics.repair)
  • Re: placing addiional caps across existing caps to reduce noise
    ... Nois Amplifier attaches to the antenna where the power has passed through ... several filter stages. ... *nothing* since there was no reason to suspect noise in the bandwidth ... I still suggest that RF is a different beast where power planes are no help. ...
    (comp.arch.fpga)
  • Re: Question in Detection
    ... a sinusoid of known power sand known frequency ... signal power to the noise power. ... The "signal" array gets the center third. ... I apply a median filter to the ...
    (comp.dsp)
  • Re: blood pressure!
    ... WIth the filter i surely agree have lot of work needs to be done! ... power is hooked up backwards, if you've got everything miswired, it's ... and mount it right next to the sensor. ... if you want and apply that pressure again, or you can just ground one ...
    (sci.electronics.basics)
  • Re: C. Cranes Twin Ferrite Antenna
    ... They won't do anything to help cancel out differential-mode noise. ... The differential mode component of the noise, by definition, is from equal and opposite noise currents on the two conductors (of the power line, for example). ... Ferrites are a good suggestion, but the ones commonly used for RFI suppression are of a ferrite type which doesn't have an awful lot of attenuation as low as the AM broadcast band. ... These will filter out both common-mode noise, ...
    (rec.radio.amateur.antenna)
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