[TenTec] RFI update

[WA2BPE]

If the 'puter is out of warranty, replacing the typical cheap pwr receptacle with one of the "Corcom type" units (the ones with the built-in dual-Pi filters) may help for EMI getting out via that route (I hv seen a few supplies with them already installed).  I am sure Ed will agree that one has to track down all the exit routes and zap them one by one.  In my experience, monitors are some of the worst offenders for direct radiation as shielding is often non-existant or a joke.  What bothers me most today about computers is the recent trend to plastic cases or cases with windows - can be interesting to look at the insides, but a disaster for EMI.  BTW, with my homemade
"clone", I burnished all the contact points on the case (common to find paint there) and added additional screws to bottle things up.

73,

Tom - WA2BPE


"Hare,Ed, W1RFI" wrote:

> My best stab at switcher noise would be to try a "brute-force" AC line filter. Radio Shack catalog 15-1111 may help.
>
> 73,
> Ed Hare, W1RFI
> ARRL Lab
> 225 Main St
> Newington, CT 06111
> Tel: 860-594-0318
> Internet: w1rfi at arrl.org
> Web: http://www.arrl.org/tis
>
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>
> > -----Original Message-----
> > From: Kevin J. Rowett [mailto:krowett at rowett.org]
> > Sent: Wednesday, June 11, 2003 11:18 AM
> > To: tentec at contesting.com
> > Subject: RE: [TenTec] RFI update
> >
> >
> > Switching power supplies tend to put out broadband noise from
> > about 150kHz
> > to
> > approximately 5MHz.  Any number of design errors can cause
> > this  - recovery
> > diodes
> > breaking down as they switch, high/low MOSFETs both on at the
> > same time for
> > an instant,
> > poor PCB layout.
> >
> > Copper tape, and ferrite beads are about the only cure.
> >
> > N6RCE
> >
> >
> > -----Original Message-----
> > From: tentec-bounces at contesting.com
> [mailto:tentec-bounces at contesting.com]
> On Behalf Of wb5jnc at juno.com
> Sent: Wednesday, June 11, 2003 7:52 AM
> To: tentec at contesting.com
> Subject: [TenTec] RFI update
>
> Greetings all,
>
> About a month ago I posted a message about an intermittent RFI problem on
> the AM BC band and 160M (which shows up spaced at approximately 138 KHz
> intervals). I had continued to try to track it down as time/WX permitted and
> had narrowed it down to my house and the neighbor behind me. Yesterday the
> neighbor's jr. op was out mowing the lawn so I went over and talked to him
> after he finished. It turns out that he came home from college about the
> time the RFI started. He brought his clone computer home that they had
> bought for him last fall when he went off to school and started using it
> here. I have checked from their QTH and the RFI seems to disappear
> completely with unplugging it -- now I need to get on the landline with him
> and check from my QTH. I had him unplug it as a secondary test because when
> it was on it _completely_ wiped out the AM radio in the hall outside his
> room with broadband noise! (BTW the computer is an "Alaska" brand: PS says
> "Made in China" as to be expecte!
>  d.)
>
> Does this sound like it could be the culprit, and if so, what's the best way
> to get it resolved? (The family is very cooperative and the system is less
> than 1 yr. old, so the question would seem to come down to whether the
> dealer or the manufacturer is responsible if I can prove that this system is
> the source of the RFI.)
>
> TNX/73, Al
>
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