AM radio noise

"Vanguard °°°" wrote:

"rcm" wrote in message
. ca...
That won't work. I try to run a battery one near the computer and
getting
within 5 ft generates interference. It is frequency dependent so it
is much
stronger in the lower AM band.

Use Internet radio to listen I guess.


Since it is RF noise, I'm wondering if there is chance that it is not
the power supply but some other component inside the system unit that
causes the interference. Have you opened the case and unplugged the
power supply from the motherboard and other devices and then powered it
on to see if the noise reappears with just the power supply running?

He said the noise appears with the systen off, i.e. the PS supplying
only stand-by power. Therefor it must be from the switching mode
stand-by part of the ATX supply.

Normally an ATX-style power supply will not turn on unless it is
connected to a motherboard. To test an ATX-style power supply without a
motherboard connection, short the PS-On signal (pin 14) to a ground
(pins 3, 5, 7, 13, 15, 16 or 17) in the 20-pin Molex connector; see
http://www.hardwaresite.net/faqpowersupply.html. Then you'll know if it
really is the power supply generating the noise or if some other
component, like a slot card, is causing the noise.

ATX power supplies usually require a minimun load to turn on. He could
leave the PS connected to a drive.

If running the power supply by itself produces no RF noise in your AM
radio, reattach the 20-pin Molex connector to the motherboard (with
power off, of course), leave all drives disconnected from power, and
remove all cards in the slots, even the video card. Power on (the boot
will fail due to the missing video card) to see if the noise is still
there. If not, power down, add a card (start with the video card), and
test again. If none of the cards are generating the noise, then start
hooking up the drives one at a time and test. What cards do you have
installed in the slots? Any tuner cards?

If you have a metal case, check that the grounding clips engage at the
bottom edges or wherever the cover slides onto the shell. If you don't
have any grounding clips to ensure the cover gets grounded to the shell,
I suppose you could try using aluminum foil folded over with enough
layers to wedge between the cover and shell but this would get damaged
when you next removed the cover and might not stay in place (I haven't
tried this so I don't know how well this works). I'm not sure what to
do if you have a plastic-only cover other than maybe spraying its inside
with metal conductive paint but that wouldn't survive much wear if you
frequently open your system unit.

See my previous replies, which cover most of the above.

Virg Wall
--
Be not the first by whom the new are tried,
Nor yet the last to lay the old aside.

On 23 Jul 2003 02:11:12 -0700, (Randy) wrote:

I've had this problem awhile but it seemed to be getting worse. My
computer pretty much wipes out my AM radio

probably not much a computer cause, but mostly monitor
intereference!!! Switch the monitor off & you will see..
very difficult solution!


-- Regards, SPAJKY
- http://freeweb.siol.net/jerman55/HP/Spajky.htm
Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
E-mail AntiSpam: remove ##

"V W Wall" wrote in message
...
"Vanguard °°°" wrote:

"rcm" wrote in message
. ca...
That won't work. I try to run a battery one near the computer and
getting
within 5 ft generates interference. It is frequency dependent so it
is much
stronger in the lower AM band.

Use Internet radio to listen I guess.


Since it is RF noise, I'm wondering if there is chance that it is not
the power supply but some other component inside the system unit that
causes the interference. Have you opened the case and unplugged the
power supply from the motherboard and other devices and then powered it
on to see if the noise reappears with just the power supply running?

He said the noise appears with the systen off, i.e. the PS supplying
only stand-by power. Therefor it must be from the switching mode
stand-by part of the ATX supply.

Normally an ATX-style power supply will not turn on unless it is
connected to a motherboard. To test an ATX-style power supply without a
motherboard connection, short the PS-On signal (pin 14) to a ground
(pins 3, 5, 7, 13, 15, 16 or 17) in the 20-pin Molex connector; see
http://www.hardwaresite.net/faqpowersupply.html. Then you'll know if it
really is the power supply generating the noise or if some other
component, like a slot card, is causing the noise.

ATX power supplies usually require a minimun load to turn on. He could
leave the PS connected to a drive.

If running the power supply by itself produces no RF noise in your AM
radio, reattach the 20-pin Molex connector to the motherboard (with
power off, of course), leave all drives disconnected from power, and
remove all cards in the slots, even the video card. Power on (the boot
will fail due to the missing video card) to see if the noise is still
there. If not, power down, add a card (start with the video card), and
test again. If none of the cards are generating the noise, then start
hooking up the drives one at a time and test. What cards do you have
installed in the slots? Any tuner cards?

If you have a metal case, check that the grounding clips engage at the
bottom edges or wherever the cover slides onto the shell. If you don't
have any grounding clips to ensure the cover gets grounded to the shell,
I suppose you could try using aluminum foil folded over with enough
layers to wedge between the cover and shell but this would get damaged
when you next removed the cover and might not stay in place (I haven't
tried this so I don't know how well this works). I'm not sure what to
do if you have a plastic-only cover other than maybe spraying its inside
with metal conductive paint but that wouldn't survive much wear if you
frequently open your system unit.

See my previous replies, which cover most of the above.

Virg Wall
--
Be not the first by whom the new are tried,
Nor yet the last to lay the old aside.

The OP still has reception problems with a battery operated radio. That
indicate a house wiring problem rather than PC wiring problem to me. I find
it hard to believe that he has static when the PC is powered off. In other
words there's lots of static when a vacuum cleaner is running but less
static with the vacuum cleaner is off. In some locations and buildings no
AM reception is possible. I'm not a radio or electrical expert but if a
battery operated radio equiped with extra wiring attached as an external
antenna doesn't reduce the static then it's not the PC causing the static.

"V W Wall" wrote in message
...
He said the noise appears with the systen off, i.e. the PS supplying
only stand-by power. Therefor it must be from the switching mode
stand-by part of the ATX supply.

Oops, forgot he mentioned that the noise disappeared when he flipped the
rear switch (to disconnect line power from the power supply).

... http://www.hardwaresite.net/faqpowersupply.html ...

ATX power supplies usually require a minimun load to turn on. He could
leave the PS connected to a drive.

The article says to use a 100-ohm resistor to provide some load on a
power tap but that's just when you want to check the voltage (since the
voltage can be different with no load). Other than fans getting noisy
or stop spinning, I haven't had much problems with power supplies (other
than when they got fried by a surge or high-voltage spike on an
unprotected host). The only thing that I remember was that an ATX-style
power supply had to be connected to the motherboard for it to turn on,
but that was probably due to a circuit for the PS-ON signal which you
can duplicate with a short when the 20-pin connector is detached from
the motherboard. According to
http://www.formfactors.org/developer...12V_PS_1_1.pdf,
when the PS-ON signal is pulled low (i.e., not open and not at TTL
high), the power supply should turn on. It does not state that there
must be a load on the power taps to have them actually provide voltages.
The +5V output should be on whether PS-ON is low (whether on or off the
motherboard connector) as long as there is AC power supplied.

Saw mention of an Antec power supply tester at
http://www17.tomshardware.com/column/20011012/ (and listed at
http://www.antec-inc.com/pro_details...p?ProdID=77003).
Wonder if it's any good; only costs $15 USD. I have come to rely on
lots of information from Thomas Pabst so I wouldn't expect him to use
something wasn't adequate for a tester.

"Vanguard °°°" wrote:

"V W Wall" wrote in message
...
He said the noise appears with the systen off, i.e. the PS supplying
only stand-by power. Therefor it must be from the switching mode
stand-by part of the ATX supply.

Oops, forgot he mentioned that the noise disappeared when he flipped the
rear switch (to disconnect line power from the power supply).

He also mentioned that he did not have a grounded line power outlet!

... http://www.hardwaresite.net/faqpowersupply.html ...

ATX power supplies usually require a minimun load to turn on. He could
leave the PS connected to a drive.

The article says to use a 100-ohm resistor to provide some load on a
power tap but that's just when you want to check the voltage (since the
voltage can be different with no load). Other than fans getting noisy
or stop spinning, I haven't had much problems with power supplies (other
than when they got fried by a surge or high-voltage spike on an
unprotected host). The only thing that I remember was that an ATX-style
power supply had to be connected to the motherboard for it to turn on,
but that was probably due to a circuit for the PS-ON signal which you
can duplicate with a short when the 20-pin connector is detached from
the motherboard.

The motherboard also removes the "turn-on" signal when the momentary
front panel switch is held closed for ~5 seconds. This is not needed
when testing a PS, but most do require a load of ~1A to turn on.

According to
http://www.formfactors.org/developer...12V_PS_1_1.pdf,
when the PS-ON signal is pulled low (i.e., not open and not at TTL
high), the power supply should turn on. It does not state that there
must be a load on the power taps to have them actually provide voltages.
The +5V output should be on whether PS-ON is low (whether on or off the
motherboard connector) as long as there is AC power supplied.

You're refering to the +5V SB output, which is generated by a seperate
small switching supply within the ATX case. This is used to supply
stand-by power for things like "start on LAN".

It also is used to start up the main PS that supplies all the other
voltages. The old AT supplies had a special transformer in the
pulse width driver that acted as a self starting blocking oscillator
and got the system going. The ATX pulse width modulator, which controls
the main switching transistors, reguires the +5V to run, hence the
"always on" stand-by supply.

Saw mention of an Antec power supply tester at
http://www17.tomshardware.com/column/20011012/ (and listed at
http://www.antec-inc.com/pro_details...p?ProdID=77003).
Wonder if it's any good; only costs $15 USD. I have come to rely on
lots of information from Thomas Pabst so I wouldn't expect him to use
something wasn't adequate for a tester.

The ones I've seen only use LEDs to check for proper voltages. They
do have a "power on" switch and a load to insure proper start up. You
really need a digital VM and a variable load to properly check out
a supply.

The input line filter in the PS, which tom_w is making such a fuss
about, can only be effective if a proper ground is supplied. Otherwise
the conducted noise has no place to go but onto the input power lines,
which then act like a big antenna to radiate the interference. The
basic frequency is ~40-50hz, but having fast transitions, it is rich
in harmonics, hence the broad band interference.

Virg Wall
--
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There shallow droughts intoxicate the brain,
And drinking largely, sobers us again. --- Alexander Pope

(Randy) wrote in message
. com...

My computer pretty much wipes out my AM radio (FM unaffected

I hooked the computer up to a belkin surgemaster with a high
frequency capacitor to no avail. I hooked my AM radio to the
same surge protector and again zippo.

Could the power supply be the culprit?

I had some cheapo PSUs with no line filters in them that drowned out
AM radios 20 feet away, even battery powered ones, but after I added
the line filter the noise disappeared almost completely.

Capacitors alone don't help because I did my testing with one of those
Belkin Surgemasters, and with the first PSU I modified, initially I
installed only the missing capacitors because I didn't have any chokes
that would fit. But after put a choke in series with each AC line,
the combination of the chokes and the capacitors eliminated the noise.
Some of these PSUs had circuit boards designed for the line filter
components, while others required replacing the power cord receptacle
with a combination receptacle/filter. I got the latter from old AT
PSUs, but even when they ran without it, they still didn't hurt AM
reception because they contained a second line filter on the circuit
board. They just must have built PSUs better in the old days.

AC power cord is a transmitting antenna between computer and
either AC line filter or Belkin protector. Just another
reason why AC line filter must be located inside power
supply. Only after using a power supply that claims to
provide such noise reduction, then other 'transmitting
antenna' possibilities can be addressed. Another solution is
a chassis ground separated from motherboard ground by a single
point connection. But until power supply does provide AC line
filtering, then all other solutions are called '****ing in the
wind'.

A power supply that does not provide specifications is
simply not acceptable and would explain Randy's original
problem. Specs are the first (but not only) fact demanded by
a consumer. Missing specs for that previously posted Radio
Shack filter recommendation also demonstrates why such
problems get created. Any acceptable power supply will make
claims equivalent to:
PFC harmonics compliance: EN61000-3-2 + A1 + A2
EMI/RFI compliance: CE, CISPR22 & FCC part 15 class B
If not provided, then assume the worst of that power supply.

RFI noise easiest to quash is from a +5 volt standby. And
yet Randy's supply appears to be *so* inferior that even the
+5VSB creates AM radio interference. His computer's assembler
- the likely original reason for his problem - may have been
that technically naive.

larrymoencurly wrote:
I had some cheapo PSUs with no line filters in them that drowned out
AM radios 20 feet away, even battery powered ones, but after I added
the line filter the noise disappeared almost completely.

Capacitors alone don't help because I did my testing with one of those
Belkin Surgemasters, and with the first PSU I modified, initially I
installed only the missing capacitors because I didn't have any chokes
that would fit. But after put a choke in series with each AC line,
the combination of the chokes and the capacitors eliminated the noise.
Some of these PSUs had circuit boards designed for the line filter
components, while others required replacing the power cord receptacle
with a combination receptacle/filter. I got the latter from old AT
PSUs, but even when they ran without it, they still didn't hurt AM
reception because they contained a second line filter on the circuit
board. They just must have built PSUs better in the old days.

"jaster" wrote in message om...
Get a battery operated AM radio.

Except the radio is my clock radio and since I quite oftem sleep in
the same room as the computer I didn't want to wake up to an alarm or
FM... I wanted news.

Randy

"jaster" wrote in message om...
Get a battery operated AM radio.

Except the radio is my clock radio and since I quite oftem sleep in
the same room as the computer I didn't want to wake up to an alarm or
FM... I wanted news.

Randy

V W Wall wrote in message ...
"Vanguard °°°" wrote:

"rcm" wrote in message
. ca...
That won't work. I try to run a battery one near the computer and
getting
within 5 ft generates interference. It is frequency dependent so it
is much
stronger in the lower AM band.

Use Internet radio to listen I guess.


Since it is RF noise, I'm wondering if there is chance that it is not
the power supply but some other component inside the system unit that
causes the interference. Have you opened the case and unplugged the
power supply from the motherboard and other devices and then powered it
on to see if the noise reappears with just the power supply running?

He said the noise appears with the systen off, i.e. the PS supplying
only stand-by power. Therefor it must be from the switching mode
stand-by part of the ATX supply.

I'm not the one who posted about the battery am radio... That's a
seond poster.
However I hadn't thought about other boards causing a problem. Even
with the power supply switched off there is still a light on my video
card (radeon 9600pro) so I guess it could theoretically cause the
interference.

I hadn't thought about the "short-out" the power supply method to see
if it's the cause. I shall try it today sometime just to make doubly
sure it's the root of the problem.

Randy