[amsat-bb] Re: "Birdies" from Linksys Wireless router

[Nate Duehr]

On May 6, 2008, at 4:58 PM, Mark L. Hammond wrote:

> Hello all,
>
> The launch of Delfi-C3 has brought to my attention a very strong  
> birdie at 145.930 MHz that clearly comes from the Linksys WRT54G  
> Wireless router that sits in the shack.  Forcing the wireless signal  
> to another frequency/channel has no impact whatsoever...
>
> Anybody on the list have a clever solution (other than 'get a  
> different router' or 'move it' or 'shut it off', etc...hi hi) that  
> they may have used for a similar problem?
>
> Thanks,
>
> Mark L. Hammond  [N8MH]


Mark,

My Linksys WRT54GS annoyed the heck out of me with birdies, so I  
replaced it with a cheap Netgear.  Not a peep out of it, since then.

I liked having DD-WRT on the Linksys device a couple of years ago when  
I was using it, but the Linksys is stashed away in a box for  
"emergencies" and otherwise banned from my shack now, due to the RF  
issues.

Ironically I had already tried the "power the house down to see if the  
interference is local" and had decided it wasn't, and that I needed to  
do some DF'ing... then I realized that the server and the WRT54GS were  
on the UPS, which I had NOT shut off.  (Doh!  Smacks forehead...)

I did try briefly to do things like ferrites on the "goes-intas" and  
"goes-outtas", etc... to no perfect effect.  I could mitigate some of  
the noise, but the thing was ultimately just too noisy.   The wall- 
wort for my particular model (there are something like six different  
hardware models of the WRT54GS -- another annoying pattern of the  
small router manufacturers) was just a transformer... whether or not  
there was a noisy switch-mode power supply inside the Linksys, I  
didn't investigate.

Someone else commented about using "quality Cat 5 and Cat 6 cable"...  
since Cat 5 and Cat 6 are ratings for UNSHIELDED twisted-pair (UTP), I  
have no idea what differing "quality" levels of cable would  
accomplish.  Ethernet via Cat 5 is SUPPOSED to leak signal.  Someone  
missed reading the standards, I guess.  The comment made no sense to  
me from an RF engineering perspective.

One possible "fix" for that type of noise could be to run Ethernet on  
SHIELDED twisted-pair (STP) cable, and ground the "drain" wire at ONE  
end (don't ground both ends, you WILL create a ground loop, and it  
WILL drive you crazy... eventually) but it no longer will meet the  
Ethernet specifications for cross-talk, etc.   Frankly, it works --  
but don't go doing it in the office or someplace where the network is  
critical.   They make special RJ45 connectors with metal strips  
"wrapped around" the connector body that can be crimped in such a way  
as to capture the drain wire, and that are built to ground to special  
female RJ45 sockets... again, only do this on one end... and they were  
usually used for things like telco T1 carriers that *are* specified to  
use STP cabling in many instances.

I don't think the real noisemaker in the Linksys was the Ethernet  
signal itself anyway -- it certainly leaked out of the cheap plastic  
(virtually unshielded) case via the Ethernet cablilng, but the  
Ethernet noise wasn't the problem.  It was so cheap to try another  
router, the "fixes" weren't worth my time.  Easier to buy from Netgear  
who's had a pretty good track record of actually building properly  
shielded products, back to when their little switches, hubs, and other  
devices were all in the "blue metal case", complete with a real ground  
terminal and lug on the back-side, which is a "body style" they're not  
making many of anymore...

Same thing with cheap plastic PC cases... noise galore leaking from  
those, too.  Makes one miss the days of steel cases and PCs you could  
barely lift.

My IBM/Lenovo T43 provided by work throws all sorts of VHF crud,  
enough to completely obliterate the front-end of my poor Kenwood TH- 
F6A "broad as a barn door" receiver on most of the VHF band (IF mixing  
perhaps), and the MacBook is more bearable, but the LCD backlight  
system makes RF noise.

I guess with the ever-lowing price of fiber-optic based networking  
gear... that's the ultimate in quiet, as long as you can keep the  
routers/switches themselves from leaking crud... but that's definitely  
overkill.  Overkill is sometimes what we hams do best, however.  I  
have seen the photos to prove it.  (GRIN)  We are the only HOBBY  
organization that regularly launches satellites... or so I'd like to  
believe.  (BIGGER GRIN)

Good luck killing off the Linksys RF interference gremlins.  Netgear  
highly recommended!

--
Nate Duehr, WY0X
nate at natetech.com