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'[EE]: Distortion of FM radio which close to PC'
2001\04\05@211216 by William

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Hi, all!

I always turn on my radio and listenning to FM channel while I am
working on
computer. Thing that always bother me is, there is always a lot of noise
(frequency
distortion) and cause my reception of the FM channel very, very bad. I
can place
my FM radio too near to my PC, always need to place it quite far away.

I am using Pentium II 300MHz. But FM band is in between something like
80 -
110MHz, why to is such a lot of frequency distortion???

Anyone got any idea to cute this problem?

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2001\04\05@215409 by Herbert Graf

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> I always turn on my radio and listenning to FM channel while I am
> working on
> computer. Thing that always bother me is, there is always a lot of noise
> (frequency
> distortion) and cause my reception of the FM channel very, very bad. I
> can place
> my FM radio too near to my PC, always need to place it quite far away.
>
> I am using Pentium II 300MHz. But FM band is in between something like
> 80 -
> 110MHz, why to is such a lot of frequency distortion???
>
> Anyone got any idea to cute this problem?

       Unfortunately PCs are extremely noisy devices, while 300MHz is a dominant
emission for you (and all it's ugly harmonics) there are ALOT of subsystems
in a PC running at lower (and possibly higher) frequencies, and since most
are square waves they emit a ton of harmonics too. There is some design to
avoid these problems. Most PC cases form a pretty tight metal box (read a
Faraday cage) so alot of the emissions are attenuated (which makes me really
cringe at the thought of those all plastic cases that have recently been
introduced, I don't see how they could pass ANY emission standard). However
if might not be you're PC, my monitor also interferes with radios, as well
as my external modem and even my mouse! I don't really know of any good
solution except moving the radio or installing an external antenna (and if
the problem still persists maybe wrapping the radio in tin foil will help!).
TTYL

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2001\04\05@224759 by William

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For curiosity, do you how those FM radio PC card (ISA or PCI) works???


Herbert Graf wrote:

{Quote hidden}

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2001\04\05@230057 by Herbert Graf

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I've always wondered the same, how TV cards work, how even sound cards works
with so much EM noise around, I guess it's just good design and ALOT of
shielding. TTYL

> {Original Message removed}

2001\04\06@012759 by David VanHorn

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At 10:58 PM 4/5/01 -0400, Herbert Graf wrote:
>I've always wondered the same, how TV cards work, how even sound cards works
>with so much EM noise around, I guess it's just good design and ALOT of
>shielding. TTYL

They are working with much stronger signals.
Just try to get a weak station on one.

Here's a tip.
From Digikey, get a couple of sheets of carbon foam, for putting ICs in.
Place in a zip-lock bag, then glue the bag to the large walls of your PC case.
I bet the noise gets better.

Shielding is reflective. That's ok, but unless you provide an absorber, the
signals bounce around until they find their way out. "Energy can neither be
created nor destroyed".. If you could measure finely enough, you would
discover that the sheets are slightly warmer than ambient.


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2001\04\06@015113 by Peter Tiang

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The PC's Front-Side Bus (FSB) is running at
100MHz ;-).

The FSB is where your SDRAM sits and the CPU
is actually accessing the memory at the FSB
speed, therefore the designation PC66,PC100
or PC133 SDRAM (66,100,133MHz speed respectively).

Cheers,
Peter Tiang

{Original Message removed}

2001\04\06@081353 by Olin Lathrop

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> I am using Pentium II 300MHz. But FM band is in between something like
> 80 -
> 110MHz, why to is such a lot of frequency distortion???

Just because the clock is 300MHz doesn't mean there aren't lots of other
frequencies being emitted.  Any sharp edge will contain a wide spectrum of
frequencies.

> Anyone got any idea to cute this problem?

Yeah, shut off the radio and concentrate on your work instead.


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Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinspamspam_OUTembedinc.com, http://www.embedinc.com

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2001\04\06@123750 by Mg

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haha!
I too was having the same problem but now, all is solved. Work efficiency
has tripled now!
Your reply reminds me of old Scrooge... bah humbug!

> > Anyone got any idea to cute this problem?
>
> Yeah, shut off the radio and concentrate on your work instead.
>
>
> ********************************************************************
> Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> (978) 742-9014, KILLspamolinKILLspamspamembedinc.com, http://www.embedinc.com
>

btw: Surpressing noise in soundcards was mentioned in a long running thread
a while ago on someone wanting to implement their own DSP using a pic.
Someone was saying that DSP methods are used on the soundcards to suppress
noise.

-Mg

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2001\04\06@134519 by Timothy Stranex

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When I switch off my flourescent desk light, my monitor goes out of suspend
mode. I think it is because some energy is induced into the mouse wires because
the screen saver is not on.

Timothy Stranex
spamBeGonetimotspamBeGonespamuskonet.com
South Africa

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2001\04\07@043749 by Peter L. Peres

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> From Digikey, get a couple of sheets of carbon foam, for putting ICs in.
> Place in a zip-lock bag, then glue the bag to the large walls of your PC
> case. I bet the noise gets better.

In this case I found that getting a largish sheet of MOS foam such that it
can be folded over the card in the slot (covering both sides and the top)
helps a little but unfortunately most of the garbage travels on the ground
and case and it is harder to get rid of. I can hear mouse and COM port
interrupts on the sound channel in my Brooktree chipset based TV card ;-(.

Again, a good quality TV card would have ground separation and be built
like a 'box in a box'. Kind of like those high end audio cards (Turtle
Beach etc) which have optical separation on board. And cost about as much
as 1.5 standard PC computers. You get what you pay for.

Peter

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2001\04\08@143727 by mmucker

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You can't filter out noise with DSP.  By definition, it's noise... there's
no way to distinguish the noise from the desired signal.  The way to
eliminate noise is to not let it in to begin with. :)

(This was said to me by a soundcard engineer who was frustrated trying to
get the digital folks to understand this about the analog audio signals.
I'm just repeating it here, and have no expertise on this myself.)

=Matt

> {Original Message removed}

2001\04\08@152414 by Sean H. Breheny

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Hi Matt,

You are correct, except that I think you are talking about random noise and
the other poster might have been using the more general term "noise" which
could refer to anything (like periodic undesired signals from the CPU,
etc.) If you know something about the nature of the noise, then DSP could
be used to reduce it.

It is probably true, though, that although in a particular case the "noise"
may be characterized and eliminated, it would be asking a lot of a DSP
system to characterize and eliminate all of the possible types of noise
that a PC might introduce.

Sean


At 01:36 PM 4/8/01 -0500, Matthew Mucker wrote:
>You can't filter out noise with DSP.  By definition, it's noise... there's
>no way to distinguish the noise from the desired signal.  The way to
>eliminate noise is to not let it in to begin with. :)
>
>(This was said to me by a soundcard engineer who was frustrated trying to
>get the digital folks to understand this about the analog audio signals.
>I'm just repeating it here, and have no expertise on this myself.)
>
>=Matt
>
> > {Original Message removed}

2001\04\09@084711 by Olin Lathrop

face picon face
> You can't filter out noise with DSP.  By definition, it's noise... there's
> no way to distinguish the noise from the desired signal.  The way to
> eliminate noise is to not let it in to begin with. :)

This is true when you know nothing about the characteristics of the noise.
However, if the noise has some characteristic that distinguishes itself from
the real signal, it is possible, in theory, to reduce or eliminate that
noise.  One of the simplest distinguising characteristics is frequency.
Noise with frequency outside the desired signals frequency range can be
filtered.  For example, it is easy to eliminate (greatly attenuate actually)
50KHz or 5Hz noise from an audio channel.

I do agree with the audio engineer though.  The best defense against noise
is to not allow it in to begin with.


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(978) 742-9014, RemoveMEolinspamTakeThisOuTembedinc.com, http://www.embedinc.com

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2001\04\09@105937 by Mg

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The post I was referring to is from the "Muso's of the world unite! ;)"
thread..
"Sure putting it external helps, but it's still real hard. It's not outside
, it's internnoise that's a problemal noise. As I say, soundcards are
generally desinged with very expensive EMI minimisation packages run by
extremely experienced engineers." By Tom Brandon (31/10/00).

So yeah after 6 months what I read has become abit hazy!

I take it "EMI minimisation packages" is referring to the overall design of
the PCB?

But anyway couldn't DSP be used to surpress/attenuate noise? Digital
bandpass filters exist so therefore isn't this DSP?

-Mg

From: "Matthew Mucker" <mmuckerEraseMEspam.....airmail.net>


> You can't filter out noise with DSP.  By definition, it's noise... there's
> no way to distinguish the noise from the desired signal.  The way to
> eliminate noise is to not let it in to begin with. :)
>
> (This was said to me by a soundcard engineer who was frustrated trying to
> get the digital folks to understand this about the analog audio signals.
> I'm just repeating it here, and have no expertise on this myself.)
>
> =Matt

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2001\04\09@120702 by David VanHorn

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At 01:02 AM 4/10/01 +1000, Mg wrote:
>The post I was referring to is from the "Muso's of the world unite! ;)"
>thread..
>"Sure putting it external helps, but it's still real hard. It's not outside
>, it's internnoise that's a problemal noise. As I say, soundcards are
>generally desinged with very expensive EMI minimisation packages run by
>extremely experienced engineers." By Tom Brandon (31/10/00).
>
>So yeah after 6 months what I read has become abit hazy!
>
>I take it "EMI minimisation packages" is referring to the overall design of
>the PCB?
>
>But anyway couldn't DSP be used to surpress/attenuate noise? Digital
>bandpass filters exist so therefore isn't this DSP?

Problem is that noise is everywhere.
You can filter out some of it, but there does not exist a "that which is
not signal" filter.
(Other than a correlator or boxcar, which works with signals of only a
single frequency.)

As far as making low noise PCB layouts, I've never heard the bit above.
I'm sure there exist expensive solutions, but I've always found that a bit
of attention to the layout and a knowlege of the basic physics involved, to
be sufficient.  I use an old but reliable cad program (dos orcad), and I
never use the autorouter.


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2001\04\09@124254 by Dan Michaels

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Matt Mucker wrote:
>You can't filter out noise with DSP.  By definition, it's noise... there's
>no way to distinguish the noise from the desired signal.  The way to
>eliminate noise is to not let it in to begin with. :)
>
>(This was said to me by a soundcard engineer who was frustrated trying to
>get the digital folks to understand this about the analog audio signals.
>I'm just repeating it here, and have no expertise on this myself.)
>


You probably misinterpreted what the soundcard engineer was saying.

The DSP books are full of techniques to deal with noise - low-pass,
high-pass, band-pass, and notch filters, plus signal averaging
statistical, and adaptive techniques. There are 10s of 1000s of
articles/etc.

However, it certainly does make sense to do everything possible to
eliminate external noise before it gets into the system. Then the
down-stream job is much simpler - this applies to "both" analog
and digital signal processing techniques.

However, you can do much the same thing with digital techniques
as with analog - except for one major difference - aliasing.

With sampling [digital] systems, as used in sound cards/etc, if you
don't have adequate "analog" filters in line before the sampler, then
hi-frequency noise can alias onto your sampled signal, and then you
never can get rid of the aliased components, and you cannot distinquish
them from signal or other noise. There are a lot of issues here.
==========


"You can't filter out noise with DSP. By definition, it's noise...
there's no way to distinguish the noise from the desired signal".

Only politicians and economists can get away with making statements
like this. You might want to search the web for basic info on signal
processing to gain some enlightenment.

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2001\04\09@143942 by Olin Lathrop

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> But anyway couldn't DSP be used to surpress/attenuate noise? Digital
> bandpass filters exist so therefore isn't this DSP?

Again, only if the noise has some characteristic that distinguishes it from
the real signal.  Suppose the noise is a 1KHz sine wave.  How is the DSP
supposed to know that the radio station isn't sending a signal that happens
to contain a 1KHz sine wave?


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Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, EraseMEolinspamembedinc.com, http://www.embedinc.com

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2001\04\09@150952 by Gordon Varney (personal)

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> > But anyway couldn't DSP be used to surpress/attenuate noise? Digital
> > bandpass filters exist so therefore isn't this DSP?
>
> Again, only if the noise has some characteristic that
> distinguishes it from
> the real signal.  Suppose the noise is a 1KHz sine wave.  How is the DSP
> supposed to know that the radio station isn't sending a signal
> that happens
> to contain a 1KHz sine wave?


As Olin is usually correct, I will not dispute him.

However, there is a process of pattern matching used in DSP, that will
remove most noise from a system.

Read the input, wait for the audio to drop below a set point for an average
period of time. Record and look for a pattern of noise, being pops and
clicks, and hiss. Then when one of these patterns are present or detected
within the normal audio, the DSP will use a negative signal to phase cancel
the noise.  Its tricky, and may remove some characterization of the original
audio but with out the pops and clicks and hiss. This is a process used in
some high end automobiles to remove road noise from the passenger
compartment.  Some recording studios and radio stations use it to remove
hiss and feed back, from the microphones.

Gordon Varney

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2001\04\10@015540 by dr. Imre Bartfai

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Hi,

I'm not sure. Noise has expected mean zero. Such way, averaging *can*
eliminate noise; you pay for it with decreased upper frequency limit. This
technique was discovered (or applied) I think by a Hungarian researcher
who made the first moon bounce experiment in 1946.

Regards,
Imre


On Sun, 8 Apr 2001, Matthew Mucker wrote:

> You can't filter out noise with DSP.  By definition, it's noise... there's
> no way to distinguish the noise from the desired signal.  The way to
> eliminate noise is to not let it in to begin with. :)
>
> (This was said to me by a soundcard engineer who was frustrated trying to
> get the digital folks to understand this about the analog audio signals.
> I'm just repeating it here, and have no expertise on this myself.)
>
> =Matt
>
> > {Original Message removed}

2001\04\10@055042 by Peter L. Peres

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>I take it "EMI minimisation packages" is referring to the overall design
>of the PCB?
>
>But anyway couldn't DSP be used to surpress/attenuate noise? Digital
>bandpass filters exist so therefore isn't this DSP?

The vast majority of the noise is caused by digital signal transitions on
the same chip. Another digital stage adding more complexity will make the
noise worse usually.

Peter

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