[Top] [All Lists]

Re: [RFI] Motherboard RFI

To: "'Dan Violette'" <danki6x@earthlink.net>, "'Peter Laws'" <plaws@plaws.net>, <rfi@contesting.com>
Subject: Re: [RFI] Motherboard RFI
From: "Wes Attaway \(N5WA\)" <wesattaway@bellsouth.net>
Date: Sat, 2 Jan 2010 13:26:19 -0600
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
Dan, here are a few ideas:

You indicate that the noise was somewhat suppressed with a snap-on choke.
This indicates to me that more choke suppression would be beneficial.  In my
experience, winding a number of turns through a doughnut ferrite of the
proper mix is far superior to one or two snap-on chokes.  You have to be
kind of lucky for a single snap-on choke to cure a noise problem.

Take a look at Jim Brown's RFI tutorial to get an idea of the proper mix and
size for the doughnut, plus other noise suppression information.

Older computers produced a lot more noise than the new ones do.  I have
built hundreds of computers over the years for clients and have not noticed
any RFI at all from a computer during the past few years.  This is with the
box and mouse and keyboard and other cables sitting within two feet of the
radio and antenna switch.

Also, you may have a problem with an imperfect coax shield connection
somewhere in the chain between radio and antenna.  I have found that loose
connectors and/or poorly soldered shields can allow ingress of noise that
would otherwise not be a problem.


------------------ Wes Attaway (N5WA) ------------------
1138 Waters Edge Circle - Shreveport, LA 71106
    318-797-4972 (office) - 318-393-3289 (cell)
        Computer Consulting and Forensics
-------------- EnCase Certified Examiner ---------------

-----Original Message-----
From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
Behalf Of Dan Violette
Sent: Saturday, January 02, 2010 12:14 PM
To: 'Peter Laws'; rfi@contesting.com
Subject: Re: [RFI] Motherboard RFI

Maybe you have bad caps on the MoBo.  Was a problem in 5-10 year old MoBos.
See:  http://en.wikipedia.org/wiki/Capacitor_plague  for some info with
references.  Suppose bad caps could be allowing unintended radiation.  /Dan

-----Original Message-----
From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
Behalf Of Peter Laws
Sent: Saturday, January 02, 2010 9:41 AM
To: rfi@contesting.com
Subject: [RFI] Motherboard RFI

Took a little time before the RTTY Roundup to try to track down some noise
on my IC746Pro.  PC was definitely the cause noise is there even if I stop
the system at the GRUB screen so likely not disk-related since they were
pretty inactive (but not a sure thing).

Pulled the cables off one by one.  Got to the motherboard's COM1 and all
noise vanished ... well, at least where I was listening on 17 m (around
18130.0).  OK, a couple snap-on chokes got rid of some but not all.  Decided
to try it on a different serial port (I have a Siig 4-port that had two free
on the octopus).  No noise.  Cool!

Not so much.  As I started to plug in other things to the motherboard (not
the PCI cards), I got the same noise there.  OK, took off the
USB-PS/2 adapter from the mouse and ran right into USB.  A little noise
there that a choke didn't really make go away - I'll try moving that to the
USB hub, but that hub still plugs into the MoBo.

Keyboard is also a problem and it's NOT USB.  Put a few snap-ons on the
cable and the AT-PS/2 adapter (yes, you read right). and again, couldn't get
rid of it all.

Opened up the case with the system running and poked around.  I noted an odd
thing.  With COM1 -- the noisiest -- connected, I could reduce the noise by
pushing on the top of some of the caps.  OK, odd.  Am I adding capacitance?
I pushed on other things, potentially conductive and not ... and got the

So what could be "loose" that would generate (I assume) common mode noise?
It's only stuff plugged into the MoBo - nothing plugged into the sound,
video, or PCI serial card.

Any ideas on a real fix?  The noise is only in specific places in the
spectrum, so I'll play in RTTY RU today/tomorrow, but now that I know that
it's actually fixable, I'd like to!


Peter Laws | N5UWY | plaws plaws net | Travel by Train!
RFI mailing list

RFI mailing list

RFI mailing list

<Prev in Thread] Current Thread [Next in Thread>