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Author Topic: RFI from Linksys non-wireless router?  (Read 4077 times)
AA1VX
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Posts: 6




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« on: April 14, 2004, 08:02:56 AM »

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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KC2MMI
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Posts: 620




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« Reply #1 on: April 16, 2004, 04:21:32 PM »

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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KC2MMI
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Posts: 620




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« Reply #2 on: April 16, 2004, 08:11:32 PM »

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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AA1VX
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« Reply #3 on: April 17, 2004, 08:25:53 AM »

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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KC2MMI
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Posts: 620




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« Reply #4 on: April 17, 2004, 02:46:33 PM »

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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KD4COX
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« Reply #5 on: April 22, 2004, 08:02:06 PM »

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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KC2MMI
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Posts: 620




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« Reply #6 on: April 22, 2004, 08:15:45 PM »

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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AA1VX
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Posts: 6




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« Reply #7 on: April 23, 2004, 06:35:08 AM »

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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KC2MMI
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Posts: 620




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« Reply #8 on: April 30, 2004, 03:32:33 PM »

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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AA1VX
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« Reply #9 on: May 02, 2004, 07:16:59 AM »

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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KD4OUZ
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Posts: 4




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« Reply #10 on: May 02, 2004, 11:59:07 AM »

I have made a similiar thread in this forum:
http://www.eham.net/forums/RFI/379

Appears we both submitted it at pretty much the same time.

Yes I have the same router, and I have a heck of alot of noise comming out of it (cable or no cable hooked up to it)

I have 8 pc's throughout the house networked, and once those Cat5's are all plugged in....it is just about useless to use 2mtr. in the house.

I have tried several other sites, on this problem, and havent got any real good response (that I have not tried out already)

My linksys is still under warranty, but Im not sure I want to send it back in.
Chances are they will not be able to fix the problem anyway, considering they are useing a plastic caseing.

I'll try to keep an eye o this post and my post to see if anyone else comes up with a good dolution that does work. Ive all but given up on this problem.
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KC2MMI
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Posts: 620




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« Reply #11 on: May 02, 2004, 04:10:42 PM »

Dave, I get a wonderful s6 crackle on 70cm when the box is plugged in, too. I didn't have a cookie tin around so I just wrapped the box in aluminum foil and folded over the edges. Guess what, "Faraday Foil" works.<G> Box gets a bit warm, so I don't run it that way.

The box is the source of the problem, with no questions about it. Since Linksys/Cisco was so clear about no warranty after 1 year, I didn't feel bad about taking a look inside, the two halves pop apart, no screws, after the tamper seal is taken off. (It glues them together.) Linksys didn't reply to the issue that there are longer federal statutory warranties against unseen defects--which I consider this to be.

There's no there there, as the saying goes. Nor, any shielding. Not even aluminized paint inside the case. I've seen that used to stop weak RFI, i.e. spray paint the inside of the case with aluminum or zinc "cold galvanize" paint and sometimes it is enough to work, without blocking any vents, etc.

But Friday I emailed the FCC asking how to pursue the issue of whether a device is defective, or perhaps simply was not built in compliance with what was submitted for ClassB testing. (Anyone here know how to formally question that?) CC'd to Linksys, too.

There were some "incidents" in the computer industry, and since Linksys made their reputation by shipping the cheapest possible boxes...I don't know, but I can suspect this box simply never should have been certified ClassB compliant. Computers generate RFI and need shielding. This one has next to none in sight.

Now there's three of us....that we know of.
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KD4OUZ
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Posts: 4




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« Reply #12 on: May 03, 2004, 06:50:57 PM »

Im wondering if anyone has found a way to get rid of the RFI from this router, other than alum. foil.

I called Linksys/Cisco this afternoon, and I must say he tried to figure out a way to get rid of the noise like, move the antenna. I mentioned to him the antenna is on a tower, which is mounted on a cement block, and I cant easily "move" the antenna. He mentioned to get the radio as far away from the router as possible. With that I mentioned there was Cat5 running all through the house and it doesnt matter where the radio is in relation to the router, because the Cat5 is like a big antenna "transmitting" all the noise from the router throughout the house.
The guy was really nice, and even wanted to hear the noise. He had me put the phone up to the radio, and turn the router on and off, so he could hear the difference.

I suppose he did all he could.
Bottom line left me with only a few options:
1. Move radio as far away as possible from router.
2. Move antenna
3. Both the above, and put the router on a different electrical circuit from the radio.

Im hoping someone out there will come up with a way to get rid of the noise. Its out of the question as far as re-routing all the cat5 so I can re-locate the router.
I can not move the antenna.
And I pretty much cant move the radio because of lack of space, and length of coax.

So......anyone else out there have any idea's on how to rid RFI coming from a wired (not wireless)router?
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KC2MMI
Member

Posts: 620




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« Reply #13 on: May 05, 2004, 01:00:51 PM »

Email my call @arrl.net and I can add your names and contact info to the complaint I've filed with the FCC.

I played nice, I gave Linksys *two* very clear chances to make some accomodation. They chose not to.
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WA2E
Member

Posts: 19




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« Reply #14 on: May 21, 2004, 06:52:58 PM »

I've also found the wallwarts can be a source of rfi. Try ferrite beads on the power cord.

Mike WA2E
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