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@natetech.com