[Boatanchors] Computer/ Switching noise

[Duane Fischer, W8DBF]

You might also post this to the list:

ham-computers at mailman.qth.net

This is an excellent list with some really bright guys who find answers that 
nobody else seems able to.

Duane Fischer, W8DBF
dfischer at usol.com
HHI: Halligan's Hallicrafters International
http://www.w9wze.net
HHRP: Historic Halligan Radio Project
http://hhrp.w9wze.net

----- Original Message ----- 
From: "Robert R. Kerr" <rrkrr at comcast.net>
To: "Dave Maples" <dsmaples at comcast.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Tuesday, January 23, 2007 9:18 AM
Subject: Re: [Boatanchors] Computer/ Switching noise


>
> I work in an office environment where everyone has a PC on their desk and 
> there are racks of server PC machines here and there.  All these machines 
> have switching regulator power supplies, which are plugged into the AC 
> power lines.  The noise from the switching regulators gets coupled to the 
> AC power line, which functions as an antenna for RF (sound familiar?) and 
> radiates from there.  Things got so bad in our building for a while that 
> it was impossible to listen to any local broadcast AM radio station. 
> Unfortunately, we also had an electronics laboratory where we needed to be 
> able to make accurate high frequency measurements, and the hash radiating 
> from the power lines interfered with this, too.
>
> The FCC has regulations for noise coming from PC power supplies, and 
> manufacturers models have to get type acceptances for all their models 
> before they can sell them in the US.
>
> What happens is that the power supply manufacturers, most of whom are 
> located in Southeast Asia, also build power supplies for PCs that go to 
> countries that don't have an FCC or any regulations regarding power supply 
> noise.  In order to save a dollar or so on the cost of each, they 
> substitute jumper wires where the series inductors in the line filters are 
> supposed to go, and do not install the shunt capacitors.  These supplies 
> can be sold cheaper than the ones with filters, and a lot of them do make 
> their way to the US anyway, where they are rarely checked after the 
> initial type acceptance test for the particular model.  This is the sort 
> of stuff you find in the really cheap computer component stores.
>
> If you've got a noisy PC power supply, have a look inside where the wires 
> from the AC line attach to the PC board and you'll usually be able to see 
> where this has been done.
>
> I've found the best cure for this is to buy "lab grade" power supplies. 
> These often cost several times what the power supplies from the cheap PC 
> stores cost, but they are usually quiet.  Personally, I've had good luck 
> with the power supplies with the brand name "Enermax", which actually 
> advertises low noise (No, I don't own their stock), but I'm sure there are 
> others.
>
> The distressing thing to me is that this problem seems to be getting much 
> more common, especially with "wall wart" type power supplies, which seem 
> to be mostly switching regulator units these days.  Right now, I have to 
> turn off my cable modem in order to use the radio because it has a noisy 
> wall wart power supply.
>
> Bob K4ERR
>
> Dave Maples wrote:
>> All: I have battled this several times over the past few weeks.  Best 
>> thing
>> I have found yet is the Radio Snack split cores.  I will take one and 
>> wind
>> as many turns of the offending cable as I can around the split core, and
>> then reassemble it.  Two of them removed the noise from a cordless phone
>> base station.  One removed noise from an LCD monitor.
>>
>> It's going to cost me a bit, but I'm eventually going to get both ends of
>> every computer, entertainment equipment, and telephone lead I have.
>>
>> My next move is to sample some of the same product from Mouser (a LOT
>> cheaper).
>>
>> All suggestions here welcome!
>>
>>
>> Dave WB4FUR
>>
>>
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>> ** List Administrator - Duane Fischer, W8DBF/W9WZE **   ** For 
>> Assistance: dfischer at usol.com **         $$ For vintage radio info, see 
>> the HCI web site $$      http://www.w9wze.org
>>
>>
>
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> ** List Administrator - Duane Fischer, W8DBF/W9WZE **   ** For Assistance: 
> dfischer at usol.com **         $$ For vintage radio info, see the HCI web 
> site $$      http://www.w9wze.org
>
>
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