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RFI from Linksys non-wireless router?
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by AA1VX on April 14, 2004
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Pleased to see this excellent forum out there.
Has anybody experienced RFI to their ham receiver from a 4-port Linksys router? It's not wireless, and is used for distributing cable-modem signals via Cat-5 cables in my house. The cable modem itself doesn't seem to generate RFI.
The interference appears as a strong carrier every 30 kHz.
No reply yet from Linksys.
Any help would be appreciated.
73,
Dave AA1VX
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RE: RFI from Linksys non-wireless router?
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by KC2MMI on April 16, 2004
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Dave, if you disconnect all the ethernet cables from the Linksys, do you still have the RFI problem?
A Linksys router doesn't "distribute" cable modem signals. In computer parlance, the cable modem is a "bridge" that takes data signals from one media (the cable TV wiring, where they are sent over a carrier around 900MHz IIRC) and translates them to a different media, your ethernet cable. Once the data leaves the cable modem--there's nothing "cable modem" about it, it is just ethernet.
The router simply distributes ethernet signals among/from the four local ports and the one line to the cable modem. It is literally one dumb computer running a *nix operating system and routing ethernet signals at 10MHz and 100MHz over the ethernet wiring, and like any other small unshielded home computer, it might be creating RFI. I have no idea what frequency the CPU in the router is running at, I'd expect that to be the RFI source in it.
It is possible that you are getting RFI directly from the router or that the ethernet cables are acting as antenna. Any long wire would be good for that, and Cat5 cabling is essentially the same as long telephone or speaker wiring in that aspect.
If the RFI is traveling over the ethernet wires, toroids would probably stop it. If the box is radiating it directly...Linksys uses cheaper plastic cases, you might look for a different brand in metal (D-Link used to make these) or try opening the box and getting creative, i.e. spray painting the interior side with an aluminum paint in an effort to shield it while still allowing ventilation? If shielding the router in aluminum foil stops the RFI...quick experiment that could give you an answer.
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RE: RFI from Linksys non-wireless router?
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by KC2MMI on April 16, 2004
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Dave, I did a little testing here with my own Linksys. Found that the WAN cable (the one to my DSL modem) seemed to be emitting a lot of TVI that I'd been planning to track down "one of these days".
Three wraps through a large (about an inch square) snap-on ferrite from all-electronics.com cleared up a lot but not all of it, but there's some TVI coming from any connection which is active, i.e. there was none over the cat5 to this computer--until I logged and started using the network. I suspect that means "until the switch connected it" since these mini-routers are also active switches.
Not sure where to take that with Linksys...and I don't have any more ferrites of that size handy. Looks like the Linksys box is one very noisy customer, and that noise is being radiated out all the cables!
I never had that problem with 10Base-2 coax...<G>...
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RE: RFI from Linksys non-wireless router?
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by AA1VX on April 17, 2004
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Jared, thanks for the posts. They've been very useful. The good news is that, based upon your first suggestion, I have tracked down the problem to one RJ-45 cable running from the router. When I unplug it, 95% of the noise is gone. The bad news is that 3 wraps around the toroid didn't stop the noise.
I'm going to try the toroid at different locations on the cable. (Ironically, it's the shortest RJ-45 cable run in my house!)
Thanks again.
Dave
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RE: RFI from Linksys non-wireless router?
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by KC2MMI on April 17, 2004
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Dave-
The good news is, I clicked on the contact link at Linksys last night and they responded early this morning. They're owned by Cisco now and they want to RMA the unit.
The bad news is, of course, that means an unknown time with no unit so I'd have to buy a replacement anyway. (I can't run my DSLmodem directly into my computer unless I install a PPPoE stack in it, and that worked so badly, it was the reason I bought the router in the first place.)
Well...off to email the wizards, and see what Cisco can do for me. Maybe an advanced swap is possible. That, and they want me to find my receipt. Right, sure, it's "somewhere in those cabinets"....<G>
But is is nice to hear a vendor say "RFI? That's our problem, let's take care of it!" instead of "Why don't you get cable?"
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RE: RFI from Linksys non-wireless router?
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by KD4COX on April 22, 2004
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You may have a cheap piece of cable... these cables are twisted pairs, with transmissions running on them at a certain frequency set (several, I don't know the set for 100base-T off the top of my head I'm afraid).
If the pairs are not inter twisted right, or it has the wrong pairs hooked up to the wrong pins, it would radiate more. I had a cable at work that when plugged between the router and switch would cause all sorts of hell. replaced cable, everything worked fine.
pick yourself up some cat-5e cables, they are not too expensive (gigabit ethernet capable). I run my own at home, never had an rfi problem from the cables. Switch? yes... I had to replace a $10 soho switch... but my network is fairly quiet now.
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RE: RFI from Linksys non-wireless router?
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by KC2MMI on April 22, 2004
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I could have a cheap piece of cable, I'm sure I do.<G>
But I unplugged ALL the cables, and the box still generates plenty of RFI. Unplugging the power stops the RFI. It comes from the box with no cables at all involved.
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RE: RFI from Linksys non-wireless router?
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by AA1VX on April 23, 2004
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Thanks for the replies. I'll re-terminate the cable in question tomorrow. I can't replace the entire cable easily because it is wired from the basement to a wall jack. I'll also check the terminations in the wall jack in case the electrician did a poor job when he installed it.
73,
Dave AA1VX
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RE: RFI from Linksys non-wireless router?
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by KC2MMI on April 30, 2004
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Dave, Cisco/Linksys is totally uninterested in the issue because my box is more than one year old and past their official warranty.
Looking inside the box, I'm not really impressed. I don't think there's anything except plastic in between most of the box and most of the world, so I can't really see a lot of RFI protection. There's a small pair of chokes in the input power--apparently simply not adequate--and no other shielding except in the RJ45 sockets, so the CPU can just broadcast through the plastic.
Have you gotten any response from them?
Has anyone else got a Linksys BEFSR41 to test for RFI? I'm wondering if the ClassB certification was bogus, or the production units were not the same as the test unit. Sadly not unheard of, with "cheapest vendor" computer parts from that time period.
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RE: RFI from Linksys non-wireless router?
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by AA1VX on May 2, 2004
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It turns out that the problem is not a single bad RJ45 cable after all. Depending on the frequency, I still get the QRM if the unit is simply turned on.
I never received a reply from Linksys after I first pointed out the problem. My next procedure will be to drop the unit into a metal box temporarily to see if that shields the QRM. If not, I'll look at a different manufacturer.
Thanks to all for your valuable input and suggestions.
73,
Dave AA1VX
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