Troubleshooting My Linksys WRT54G Router for RFI

An adventure in locating RFI
 by
John Scott,  K8YC
Udated 7-19-2013

I had noise spurs about every 30 khz on the 6m band on my radio. I've owned the same Linksys WRT54G Router/Access Point for at least 5 years and never dreamed it could be the source of such problems. I always thought my problem was a local noise source outside the house until I moved in March 2013 and the noise followed me to the new house!

Earlier, I had snooped out a problem on 6m with spurs every 58kHz to my wife's treadmill.  If left "on" with the DC motor speed chopper circuit running the noise was there. Only if I turned off the main power switch did the noise go away.  Needless to say with that sluething behind me, I couldn't imagine the problem was coming from my Linksys router.  And, besides the noise was only on 6m (I think???) and I seem to only be scouting six meters from April to August in most years.

So, when a visiting ham saw my S9 noise spur on 6m (one was at 50.119MHz in the DX Window and the other was at 50.149MHz an active portion of the band for grid hunters), he encouraged me by offering help as I turned off various devices.

We started with the PC and the monitor right in the shack.  We mused together about what was common to both houses.  The treadmill had since been donated to Habitat For Humanity.  About the only things that were the same was my HP LaserJet and my Linksys Router.    My router and LaserJet is upstairs--about 12 feet over my head in the radio shack.  Both were at the old house, and both are left on all the time.  Switching the LaserJet off resulted in no change.

Then, with the WRT54G unplugged, the noise was GONE!

A quick query on the Internet seems to show that Cisco acquired a dog in Linksys.  I'd been in data communications in my career, and Cisco seemed to always build top notch gear.  There is no doubt that my Linksys product has worked flawlessly in doing what it was supposed to do,  and I had great faith in the Cisco name when I bought it.  Yet when such a behemoth as Cisco takes on as small an acquisition as Linksys must surely have been, primarily operating in the consumer electronics marketplace, I guess there were bound to be some hiccups.

What bothers me most is the blase' attitude by the technical staff.  I guess I'll write a note to John Chambers at Cisco. Writing the CEO of a company with a reasoned letter usually gets results because the CEO often is insulated from such problems, and Cisco should not be putting out "noise-makers".

--John Scott,  K8YC

An update as of 7/19/13:

Today, I turned on the rig because there was a juicy contact spotted in the Mariana's Island chain on 20m.  Alas, when I got there, he had moved on.  I then began wondering if the Linksys-generated noise spurs I came to know based upon clues from your website were as bad on 10m which is a little more than one-half the 6m band frequencies where I found my problem. 

Sure enough on a quiet 10m band, I found the same sequence of spurs, again all with 30kHz separation.  I had the XYL listen for me as I again went upstairs to pull the plug on the Linksys.  And, waddyaknow?  The noise was gone--AGAIN.

 Something I had read somewhere suggested there might be a switching power supply in selected  "wall warts" that created the noise.  That seemed improbable, because the heft of the wall wart suggested it was nothing more than a small transformer.  Nevertheless, I substituted a similarly rated 12v wall wart, and the noise remained.  Finally, a trip to the pantry netted a suitable sheet of aluminum foil.  Wrapping the foil around the electronics box alone and then the entire router, including antennas would not suppress my Linksys Noise Beacon.  I had already put a Type 43 toroid on the 12v DC connection from the wall wart, just in case the RFI was radiating from the power cord.  No luck there, either.

So what we have here is a Part 15 Electronic device that has S7 to S9 noise spurs within 50 feet of the device present on 28MHz and 50MHz (and everywhere in between????).  It is surely time to write a letter to a corporate executive.

--John, K8YC

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