AM radio noise

[Randy]

I've had this problem awhile but it seemed to be getting worse. My
computer pretty much wipes out my AM radio (FM unaffected). All the
wall sockets in my room are on the same circuit so I'm out of luck
moving the radio. Now... I expect the AM radio to go bonkers if the
system is on but this happens when the computer is off too. If I
switch the power supply to off in the back of the case all is well. Is
this normal?

The graphics board always has a light on (Radian 9600 pro) for the 8x
agp but I wouldn't think this would have that kind of affect. 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? If so are there ones on the
market anyone could recommend that wouldn't contaminate the AC line of
the house?

Thanks

Randy

 

[Conor]

I've had this problem awhile but it seemed to be getting worse. My
computer pretty much wipes out my AM radio (FM unaffected). All the
wall sockets in my room are on the same circuit so I'm out of luck
moving the radio. Now... I expect the AM radio to go bonkers if the
system is on but this happens when the computer is off too. If I
switch the power supply to off in the back of the case all is well. Is
this normal?

The graphics board always has a light on (Radian 9600 pro) for the 8x
agp but I wouldn't think this would have that kind of affect. 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? If so are there ones on the
market anyone could recommend that wouldn't contaminate the AC line of
the house?

THe problem is that a modern ATX PC is never really off, more like a
standby.

The only thing you can really do is make sure all the leads for the PC
are wrapped through ferrite rings to eliminate as much RF noise as
possible.

It may be though that the PC isn't the culprit.

--
________________________
Conor Turton
(e-mail address removed)
ICQ:31909763
________________________

 

[w_tom]

Common problem when that computer expert selected a power
supply based upon price rather than on technical specs. Power
supplies must have an in-line filter. But many important
functions are forgotten to sell power supplies at less than
$80. Missing functions when a power supply is not provided
with a long list of specifications including:
PFC harmonics compliance: EN61000-3-2 + A1 + A2
EMI/RFI compliance: CE, CISPR22 & FCC part 15 class B

Where does that surge protector even cite numbers for noise
reduction? It remains inert - does nothing - until voltages
above 300 volts are observed. But then even that number is
often in small print. Again, if no specifications, then why
would you assume something will work only based upon an
arbitrary comment (such as high frequency capacitor). Once
numbers are provided, then surge protector does not even claim
to address your problem.

First confirm the power supply claims to provide a long list
of essential functions, or replace it. Cheap power supplies
can even contribute to damage of other computer components.

 

[Vanguard °°°]

I've had this problem awhile but it seemed to be getting worse. My
computer pretty much wipes out my AM radio (FM unaffected). All the
wall sockets in my room are on the same circuit so I'm out of luck
moving the radio. Now... I expect the AM radio to go bonkers if the
system is on but this happens when the computer is off too. If I
switch the power supply to off in the back of the case all is well. Is
this normal?

The graphics board always has a light on (Radian 9600 pro) for the 8x
agp but I wouldn't think this would have that kind of affect. 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? If so are there ones on the
market anyone could recommend that wouldn't contaminate the AC line of
the house?

Thanks

Randy

Sounds like you need a line noise filter for your AM/FM radio, like at
Radio Shack (http://tinyurl.com/htqm). However, I don't think you can
use it for your computer as its function is to eliminate line noise from
the input side, not getting introduced from the output side. All other
devices will also be affected by the noise that your computer power
supply is putting on the line, so you might want to plan for a better
power supply.

 

[w_tom]

Filter is not unidirectional. However a filter superior to
that Radio Shack product must be inside the power supply. Too
many computer experts don't even have basic electrical
knowledge. Therefore many clone computers have power supplies
selected only on one specification - price. It is called the
MBA mentality. Inferior power supplies can be dumped into N
America at even greater profit because too many N American
technicians don't even know what a power supply is suppose to
do - never read specifications - don't even have basic
electrical knowledge.

They are called low pass filters. They work in either
direction. Nothing technically advanced about that electronic
knowledge. Would be nice if Radio Shack gave even one
specification other than price. But then this filter, like so
many computer power supplies, is also being recommended
without any technical knowledge - no number or specifications
need be provided.

Buy a power supply for $40 that is missing many essential
functions including that low pass filter. Then spend another
$40 for every other appliance to filter the noise. This is
why cost controller mentalities cause major cost increases.
Until a minimally acceptable power supply is installed, then
all other solutions are wasted money and time.

Minimally acceptable starts at about $80. If noise is not
quashed at the source, then every wire connecting to that
computer becomes a potential transmitting antenna.

Noise filter is not required. The problem first must be
fixed. Solution starts with specifications.

 

[jaster]

Get a battery operated AM radio.

 

[rcm]

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.

 

[V W Wall]

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.

There are two kinds of RF interference, conducted (usually through the
power lines), and radiated, directly through the air. PC cases are
supposed to shield against radiated interference, but openings in the case,
poor contact between side panels, etc. can negate this. As w_tom says,
the PS should have line filtering for conducted noise. (The FCC requires
units sold in the US to pass tests for this.)

All switching power supplies generate RF interference over a
fairly wide band. Even when "off", the ATX PS has a stand-by supply
that is constantly on when line power is supplied to the unit.

Since a battery receiver still has problems, it is a radiated RF
signal that is the culprit. You might try a better ground on the
computer case than that supplied by the line cord. Check for any
openings other than those required for air flow, and make sure these
have metal grills.

Wrapping the receiver in aluminum foil grounded to a water pipe,
might be a brute force way of stopping it's reception of the PS
radiated energy. You would then need an external antenna connected
by a shielded co-ax, as someone has suggested.The PS generated noise
is usually at about 40Khz, but it has strong harmonics well into
higher bands.

Virg Wall

 

[Vanguard °°°]

Try to propose solutions that Randy can actually implement. Yes, he can
replace his power supply with a better unit. You're assuming he has
$80, or more, to waste on a new power supply AND that he is going to
install it rather than having to pay a shop to install it. Preaching
the best solution regardless of financial constraints doesn't help.
Others had already offered (or I expected others to offer) the high-road
solution, so I proffered a lower cost solution. I didn't say it was the
best solution. I just offered it as one possible solution and a
different one than the expected solution. There is no point to post a
"me-too" duplicate solution; a dozen replies of "get a better power
supply" doesn't give Randy many options for a solution. Of course,
another suggestion might be that Randy build a massive antenna with
active filtering and shielding just for his little AM radio but that
would be pointless without regard to Randy's financial, educational, and
physical constraints.

Ranting about the use of low-quality components as being a problem with
lack of education in techs regarding specifications doesn't help Randy,
either. It just illustrates that you are pissed off about the situation
but also that you don't seem to realize that it is the consumers that
dictate the use of low-quality components in low-priced consumer-grade
computers. Buy cheap, get cheap. Wow, what a revelation. MacDonalds
and BurgerKing exist because there are enough consumers that want
low-priced low-quality food. Same for computers or any other product
where enough consumers are willing to sacrifice quality to get a cheap
price. The business of business is to stay in business so you sell to
whomever is willing to buy for whatever they want to buy at the price
they will pay. Using cheap power supplies has nothing to do with the
lack of education by techs but has everything to do with consumer
economics. Randy probably cannot effect a change in the industry or
influence a worldwide populace of consumers, so stop spewing farts at
him about problems in the industry (which is simply matching consumer
demands) or that these low-grade low-priced components don't follow
specs (since it is obvious to everyone that paying the lowest price does
NOT result in getting the highest quality).

You are also lambasting Randy that he has a cheap power supply.
Components (within components) do fail, so maybe his power supply was
okay but went bad and he needs to get a new one - but another one of the
exact same model might be just as good and resolve the problem without
having to waste money on a solution that far exceeds his requirements.
Your kid wants a wrist watch. Do you get him a $20 Timex or a
mega-grand Rolex? Both are solutions but obviously one fits better
within your financial constraints.

I expected other posters to state the obvious solution and Randy already
suspected the power supply, so I provided a different solution rather
than fixating on the most costly, most time consuming, and most
disruptive solution.

 

[Vanguard °°°]

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?

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.

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.

 

[V W Wall]

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

 

[Spajky]

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 ##

 

[jaster]

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.

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

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

Virg Wall

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.

 

[Vanguard °°°]

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).

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/specs/atx/ATX_ATX12V_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_accessories.php?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.

 

[V W Wall]

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!

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/specs/atx/ATX_ATX12V_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_accessories.php?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

 

[larrymoencurly]

(e-mail address removed) (Randy) wrote in message

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.

 

[w_tom]

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 'pissing 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.

 

[Randy]

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

 

[Randy]

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

 

[Randy]

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