eHam Forums => RFI / EMI => Topic started by: AA1VX on April 14, 2004, 08:02:56 AM

Title: RFI from Linksys non-wireless router?
Post by: AA1VX 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.


Dave AA1VX

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI 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.

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI 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 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>...

Title: RFI from Linksys non-wireless router?
Post by: AA1VX 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.


Title: RFI from Linksys non-wireless router?
Post by: KC2MMI on April 17, 2004, 02:46:33 PM
 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.) 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?"

Title: RFI from Linksys non-wireless router?
Post by: KD4COX 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.

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI 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.

Title: RFI from Linksys non-wireless router?
Post by: AA1VX 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.


Dave AA1VX

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI 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.

Title: RFI from Linksys non-wireless router?
Post by: AA1VX 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.


Dave AA1VX

Title: RFI from Linksys non-wireless router?
Post by: KD4OUZ on May 02, 2004, 11:59:07 AM
I have made a similiar thread in this forum:

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 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.

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI 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.

Title: RFI from Linksys non-wireless router?
Post by: KD4OUZ 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?

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI on May 05, 2004, 01:00:51 PM
Email my call 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.

Title: RFI from Linksys non-wireless router?
Post by: WA2E 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

Title: RFI from Linksys non-wireless router?
Post by: KC2MMI on May 21, 2004, 07:08:36 PM
 A good thought. But the wall wart in this case is not emitting RFI, there is no noise from the wall wart. Once you plug it into the router, the router beings emitting gobs of RFI/TVI. Unplug it--without turning off power to the wall wart--and the problem goes away.

 The problem is in the routers. At least, I've neer heard of a computer being built in a plastic case, with no shielding over the MB and CPU, that could meet ClassB certification. Except maybe my Palm, but Palm's were built by better "parents" than most computers.<G>

Title: RFI from Linksys non-wireless router?
Post by: AA1VX on June 06, 2004, 01:45:37 PM
I finally got around to putting the router into a cookie tin with just the RJ-45 cables sticking out, but the interference was still there.

I guess the next step is to buy a router from a different manufacturer.

Any suggestions on which one(s) won't cause QRM on the ham bands?

Thanks again, all.


Dave AA1VX

Title: RFI from Linksys non-wireless router?
Post by: K7NA on June 06, 2004, 06:57:15 PM
     I also am experiencing interference in the form of numerous phantom carriers up and down the 6-meter band which trace back to my plastic encased D-Link Dl-604 router. I've tried ferrites on the router power cable both near the wallwart and near the router itself to no avail. I can unplug the Cat5 cables leading to the SB5100 cable modem and to each computer with no effect on the 6-meter interference. The only thing that solves the problem is to unplug the power cable and thus power down the router.  
    As I indicated, my noise appears as numerous carriers across the 50 mHz band. I do hear a "frying noise" at some spots on the dial on 6-meters as well as HF and I suspect it is coming from somewhere in my neighborhood, not from my house and not from my router because it does not disappear when I remove power from my router.  Interestingly, another source of interference I located in my house was my wife's fax machine! Just plugged in, the machine created a noise approximating that from flourescent lights on HF.
     Yesterday, I purchased (temporarily) another router (Netgear RP614 encased in plastic) and installed it in place of the D-Link unit. Other than a slight shift in the frequency of the phantom carriers that appear up and down the 6-meter band at various signal strengths, no improvement was noted at all. I immediately returned the Netgear unit to the store. Next, I plan to purchase a metal encased router to  ascertain whether that affects the level of noise.  Like many, I am not in a position to change the location of my computer, router or ham antenna. On 6-meters, I use both a Diamond DP-GH62 vertical and a Par Omniangle loop and both pick up the router interference.
     If someone finds a real cure for this interference, by all means, please share it with us!


Title: RFI from Linksys non-wireless router?
Post by: AB0KB on June 12, 2004, 03:20:10 PM
Add us to the list.  We recently installed a Linksys non-wireless router and it completely took out our "home" 2m frequency.  We have been running a netgear for a while (family of four, all hams and techies, we actually intend to run both routers...) and have not noticed any interference from it.  It sounds to me like the FCC cert was bogus.  Maybe Hollingworth would be interested in this case?  We have all our routers, most of our hubs (except the wireless one a couple in other rooms) and broadband modem co-located in a little "nook".  Given the experiences of others, I think the easiest approach for me (that has good odds for lots of significant improvements) is to build a mini-screenroom mounting enclosure and put all our network stuff in it.  I'm interested in what others are doing and (should I get to this project in a reasonable amount of time) I'll let you know how it goes here.
Steve, AB0KB.

Title: RFI from Linksys non-wireless router?
Post by: AB0KB on June 12, 2004, 05:51:36 PM
Here's a quick, and discouraging, update.  Before going to the effort to build the cabinet, I did the "rapid proof-of-concept" test.  I have a lot of surplus copper tape, so I took the router apart and carefully copper-taped the entire inside of the case (repunching the air and LED holes).  It's clear the pcb designer was assuming a conductive case as the one mounting screw through-hole on the pcb (to screw into the case) has routed to it the ground plane and the drain wire for the shields around the network connections.  I made sure my copper shield made the connection with the pcbs single point shield ground.  Although there was improvement (I can at least squelch it on the 2m in my lab) but is still stinks.  I can't squelch it on the family room's 2m (in the same room as the router).  By the way, if you google "linksys router RFI" you get a ton of hits.  One of the threads I was reading mentioned an existant class action suit against linksys.  Don't know if that real or not as googling "linksys RFI class-action lawsuit" didn't hit anything real.


Title: RFI from Linksys non-wireless router?
Post by: AB0KB on June 12, 2004, 09:29:24 PM
This time my quick update is an encouraging one.  I dug 5 surplus torroids out of my "passives" drawer (Fair-rite #65 material 1.142" O.D., 0.746" I.D., 0.545" Length, not in the catalog so it may not be available off-the-shelf) and put one on each network cable connecting to the router (3T each). This plus the shielding I added earlier, did the trick.  The router RFI is no longer audible on any of my 2m rigs.

Clearly this router (Linksys BEFSR41) is AWFUL on BOTH conducted and radiated emission. But if your junk box is as deep as mine it's a pretty easy fix.


Title: RFI from Linksys non-wireless router?
Post by: KD4OUZ on June 13, 2004, 09:19:25 AM
I have no way of getting any ferrite beads. Guess I should do a little surfing on the internet. If thats the case of correcting this, I would have to have beads on the power cord, and all of the CAT5 I have.....4 from the linksys router and four from a 8 port hub which also seems to transmit the linklsys routers RFI, cause one of the cables has to be pluged into the linksys (main hub)to get the internet signal to the 8 port hub.

This is starting to sound like a pain, and possibly costly...and I would imagin no gurantee of the results.

Its a soon as you walk into my house your 2mtr. reception is totally whiped out, cause of all the cat5 in this house  :(

Title: RFI from Linksys non-wireless router?
Post by: AB0KB on June 13, 2004, 06:02:59 PM
I don't agree with the details in your message but we may be in agreement on the big picture...

I only put toroids on the five network cables going directly into the linksys router.  And I did it right at the router.  I did not put any beads on other cables and our "home" network includes a wireless hub, two sixteen port hubs, an eight port hub and a Netgear router (in addition to our Linksys).  We have cat5 cable running all over the place.  I did not put any toroids on any power cables either.  At our house, only the linksys was an RFI piece of crap.  Everything else appeared to be built according to law (Admittedly my words are harsh here but having put electronic equipment though RFI testing myself, I seriously doubt the linksys router, in the configuration we purchased it, was ever legitimately tested as required by law)

However, your conclusion that, since you don't have the right junk on hand (as I did) that it may not be worth going and buying it, is probably correct.  On another Forum (I forget which one) which I found when reading up about linksys RFI yesterday some advice was given that I believe to be very sound (even though I didn't really follow it).  The advice was don't try to fix your cables, they are not the problem.  If you have a linksys router, hit is with a sledge hammer and your RFI problems will go away.  Then spend the same amount of money for a correctly manufactured router that you would have spent on "fixing" your cables etc. and get better results.

If you do decide the go the challenging route, you will need to completly enclose the router in shielding in addition to putting Ferrite on the network cables you plug into the Linksys.  Neither shielding, nor Ferrite will fix it on their own.  You need both.  

I happened to have surplus copper tape and ferrite toroids on hand (plus I love the challenge of figuring out and fixing other people's electronic screwups, it's a great way to reduce the frequency of my own).  Otherwise I doubt I would have handled it the way I did.

Good luck and best wishes,

Title: RFI from Linksys non-wireless router?
Post by: K7NA on June 22, 2004, 01:09:43 AM
I've tried two plastic-encased routers for my wired high speed internet service and both (a Netgear and a D-link) were horrible for creating carriers across the 6-meter band. I purchased a refurbished metal-encased Netgear RP-114 for $14.95 on Ebay last week and after placing it into service found a significant improvement in the noise situation. The carriers across the band are now down around S1-2 or weaker. I plan to wrap each Cat5 cable in a toroid and hopefully, that will reduce it even further. It appears a properly installed, metal-encased router is quieter than the popular plastic boxed units out there on the shelves of Best Buy, Office Depot, etc.  


Title: RFI from Linksys non-wireless router?
Post by: AA1VX on June 22, 2004, 09:53:24 PM
I ordered a refurbished RP-114 Router today. It has a metal case and hopefully will not act as a noise transmitter throughout the HF bands. I'll post the results to this forum after I receive it and put it in place.

Thanks for all the suggestions thus far.


Dave AA1VX

Title: RFI from Linksys non-wireless router?
Post by: XYZZY on June 29, 2004, 08:13:34 AM
I hope I'm not intruding. I am not a ham radio operator. Just wanted you to know that I'm experiencing similar problems with my SMC Barricade 7004ABR non-wireless router. The RFI I get is on the AM band on every radio in my home. When I power off the router, all my AM radios work fine. More RFI above 1MHz than below. I read that sometimes a ferrite core on the router power cord will reduce the RFI. Where can I get more info on this solution? Can I build my own? Or do I need to purchase it? Anyway, I'm in contact with SMC support and will post here any useful info they provide.


Title: RFI from Linksys non-wireless router?
Post by: KC2MMI on June 29, 2004, 09:38:02 AM
 <Where can I get more info on this solution? >
Well, you can ask SMC to deal with it. Or, you can get sucked into ham radio.<G>
 These "home computing" devices are supposed to be FCC ClassB certified to not cause interference in a home environment. I don't know if yours is a "home" device or an "office" device and, thanks to government logic, "office" devices only have to be ClassA certified which allows them to make MORE noise not less. This must be the only spec where getting an "A" means less than getting a "B".<G>
 There are lots of web sites you can turn up by searching on "solving RFI" or "reducing RFI" etc that should give you more info. If the SMC was emitting noise only via the power cord, then yes a choke (aka ferrite) might stop it. There are some technical issues about which kind from who might work better...that's where you wind up getting sucked into the hobby.<G> It might be easier, if that SMC runs on 9v-12v dc, to try running it from a gel cell or other isolated power supply first. If it still makes the noise--which it probably will--then looking into a choke on the power cord won't accomplish anything.

Title: RFI from Linksys non-wireless router?
Post by: XYZZY on June 29, 2004, 06:53:40 PM
Thanks for the advice. I think I'll try your "battery" solution first. If that doesn't help I may just buy another router - they're not that expensive now.
I'm also waiting for some feedback from SMC. Also, according to the documentation, this router is certified Class B.


Title: RFI from Linksys non-wireless router?
Post by: KC2MMI on October 10, 2004, 05:36:37 PM
Guys, after all these months the FCC still hasn't said "boo". (Although, perhaps they will on the 31st?)

But the ARRL's Laboratory Manager and RFI specialist, Ed Hare W1RFI, has shed some light on this.

"...above 30 MHz, the device has radiated emissions limits.  That is 100 uV/m 3 meters from the source, or +40 dBuV/m.  To put that in perspective, on VHF television, a "Grade B" signal on channel 2 is +47 dBuV/m so the signal from the unlicensed device is only 7 dB less than the TV signal in the clear. If that unlicensed device is being used indoors near a TV with rabbit ears, interference is inevitable."

Simply put, the FCC ClassB certification limit is apparently so high at VHF frequencies, that a ClassB certified device can and will squeal like a pig and still be in full compliance. The fact that most home computing devices create no problem at all, is apparently a credit to DEC, COmpaq, HP, IBM, and the many small shops that manage to build much more complex devices--which don't create any RFI at all.

And a further credit to those fine folks who say "HI! We're from the government and we're here to help you!"

Title: RFI from Linksys non-wireless router?
Post by: W4DJ on September 07, 2007, 11:59:20 AM
Yes I have a BEFSR41 and have the same problem here with RFI on 2 144 and 400 mhz.
I have tryed all the recommended fixes but its still there coming from within the unit, as soon as I pull the power plug the RFI is gone!