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One Solution to Wireless Router RFI

Floyd Sense (K8AC) on August 16, 2005
View comments about this article!

I recently installed a wireless router (D-Link model DI-524) to connect a wireless LAN to my broadband cable modem. Finally got around to checking for RFI from the router and found a number of discrete signals on 160, 80 and 40 meters. The signals were typical of those from noisy switching power supplies, i.e., unstable, wide, modulated, drifting around a bit. The problem turned out to be the 5V 2.5A switching supply in the plug of the router. While I could reduce the signal amplitude a bit using chokes and ferrite rods, the worst of them was still S3 on 40 meters.

In looking around for a low-cost linear supply to provide 5V power at 2.5A or thereabouts, I came across a real deal - a new-old-stock 5VDC 3A supply that cost only $2.50. Here's where I found it:

LINK

I have no connection with the seller, and you can probably find other sources of this or a similar supply on the Internet. The supply fit nicely into an old two-port serial port switch box. When I fired up the router using this new supply, all the spurious signals were gone and the bands were quiet again.

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One Solution to Wireless Router RFI  
by K0BG on August 16, 2005 Mail this to a friend!
I guess I'm lucky. I have a Netgear box which also uses a switching type wall wort. If it makes any RFI noise, I haven't discovered it. While these style of devices leave little room for proper RFI suppression, on average I find them fairly quiet RFI wise. The only one I have which generates a significant amount of RFI is the one supplied with my Remington shaver. Thank goodness it doesn't have to be plugged in all of the time.

Alan, KBG
www.k0bg.com
 
RE: One Solution to Wireless Router RFI  
by AA4PB on August 16, 2005 Mail this to a friend!
Much of the RFI differences probably depend on the antenna installation. In my case the antennas are all on the tower about 100 foot away from the house and I generally don't have any RFI issues.
 
One Solution to Wireless Router RFI  
by N0AH on August 16, 2005 Mail this to a friend!
Switching power supplies are like a box of chocolates.............
 
RE: One Solution to Wireless Router RFI  
by KA4KOE on August 16, 2005 Mail this to a friend!
Didn't know wall warts could be that noisy. I've got it bad on 6 meters here.
 
One Solution to Wireless Router RFI  
by W8JJW on August 16, 2005 Mail this to a friend!
My main culprit for this type of noise turned out to be the rather large 12v power supply used with the lawn sprinkler controller. I put a type 73 bead on the lead, which helped, but noise is still noticeable across a fairly wide frequency range in the low VHF spectrum, inlcuding TV channel 5.
Maybe a bead better suited to VHF would help more.
 
One Solution to Wireless Router RFI  
by WA1RNE on August 16, 2005 Mail this to a friend!
This is a good, cheap solution.


However, the wall switcher EMI can be "tamed" using other techniques in combination with the first one you tried - the common mode choke.


Sometimes, adding differential mode filtering is required in addition to the common mode choke.

This is a little more difficult as it requires adding inductance to each output line of the switcher as close to the switcher as possible. This requires cutting each line and adding a ferrite bead over each wire (some you can wind more then 1 turn depending on the size) then splicing the wire back together with solder and shrink tubing.

In combination with this approach, add the common mode choke at the switcher end and/or at the end of the cable near the router.

Should make a big difference.


73, Chris
 
RE: One Solution to Wireless Router RFI  
by W7KKK on August 16, 2005 Mail this to a friend!
I went with a wired router for the computers.
I also went with the wired WX station by Davis.
No problems, so far.
 
RE: One Solution to Wireless Router RFI  
by AA4PB on August 16, 2005 Mail this to a friend!
Wired or wireless - they both generally use switching power supplies. It would be rather unusual for the RF portion of the wireless to get into an HF/VHF/UHF receiver because the frequency is so high.

 
One Solution to Wireless Router RFI  
by N7UQA on August 16, 2005 Mail this to a friend!
Even though this story has been touched on here before this is not an unheard of problem. It always can be traced to poor engineering or the manufacture trying to pull a fast one. I have found that a lot of the crap coming from China wouldn't meet part 15 acceptance. It turns out that the product is submitted for testing with all the necessary components to keep it part 15 compliant. Once acceptance is granted, the manufacture leaves these components out.

A few years ago I bought a computer case with supply to build a computer for the radio room. Once I had everything connected I turned the computer on, I was greeted with S9+60 of hash on 160-20 meters. I took apart the supply and found that ALL the RF chokes were replaced with jumpers and ALL the bypass capacitors were never inserted into their place on the board.

I had a Linksys router that also had a noisy switching supply, I replaced it with a supply out of a old Macintosh LC III and the problem was solved.


Craig - N7UQA
 
RE: One Solution to Wireless Router RFI  
by WM5Z on August 16, 2005 Mail this to a friend!
"A few years ago I bought a computer case with supply to build a computer for the radio room. Once I had everything connected I turned the computer on, I was greeted with S9+60 of hash on 160-20 meters. I took apart the supply and found that ALL the RF chokes were replaced with jumpers and ALL the bypass capacitors were never inserted into their place on the board. "

Although it might be pointless, if all of us were to demand from the manufacturer a replacement that meets FCC regulations, they would soon find that replacing this junk would cost more than what they saved by stealing from us consumers.

Steve/WM5Z
 
RE: One Solution to Wireless Router RFI  
by KB9YGD on August 16, 2005 Mail this to a friend!
well ya think that is bad i have verizon adsl and a westel dual connect adsl modem and man you can work dx with this modem it has 20 db over s9 signals on all bands and i have to unplug it to use 40 meters im thinking about selling the other radios and using it now just connect it to the antenna,hi hi 73 ``The Real Ham``
 
RE: One Solution to Wireless Router RFI  
by K8MHZ on August 16, 2005 Mail this to a friend!
I looked at the listing and found the cost to be $11.

$2.50 plus $8.50 shipping. Shipping (profit) is not refundable. One of the oldest tricks on eBay.

Has anyone tried a power supply from computer cases? They have both 12 and 5 volt outputs. I am not sure of the current available, nor the amount of noise generated. If they do work, I have a dozen or so I would actually pay $2.50 each to get rid of. Shipping, of course, will run $15.00 each, and is not refundable. If I send you a bad one, simply send me back the part and I will gladly accept the $2.50 I paid you to take the part in return.

73,

Mark K8MHZ

(Obviously the only part of the above that was serious is the question about using the old power supplies)
 
One Solution to Wireless Router RFI  
by K8VF on August 16, 2005 Mail this to a friend!
My problem is that my H.F. station knocks the dsl modem out of synch.

Anyone have this and fix it?

Shielded cables, chokes, to no avail.

5 watts on 160 meters knocks me off line.

Same phone line, 500 watts is no problem with modem in computer.

Any links or ideas will be appreciated. I will BUY a modem again if someone shows me it is r.f. proof.

Mine is a Netopia 3300 series Cayman.

Thanks for your article, I'll use some of the hints.

Mark
 
RE: One Solution to Wireless Router RFI  
by N2WEC on August 16, 2005 Mail this to a friend!
Who would leave themselves open to all the hacking. No wireless system is safe. A big chance I am not willing to take.......
 
One Solution to Wireless Router RFI  
by N7ZM on August 16, 2005 Mail this to a friend!
Guess I am lucky also. Use a Cisco Linksys WRT-54G wireless router and have no RF problems into my FT-1000MP MK-V, and my computer and router are just 2 1/2 feet away from my rig.
73, Ron N7ZM
 
RE: One Solution to Wireless Router RFI  
by KC0TQX on August 16, 2005 Mail this to a friend!
Well, a lot of times people use wireless because a wired network is either impractical or impossible. For example, I live in an apartment, and we can't really rewire the building. So, I have a wi-fi net connecting my computer in my bedroom with the cable modem in the living room. Been doing that for 2+ years. I know for sure a lot of wardrivers would skip over our network because there's another one not too far away with SSID 'linksys' and no encryption. Much easier target.

Anyway, sometimes I've noticed interference on 20M when the network has been active, like when I'm surfin' the 'Net or whatever. It sounds very similar to the interference I hear on our 2.4GHz cordless phone during the same situation. What I can't figure out is how 2.4GHz activity is causing interference that low on the spectrum. Any thoughts, anyone?
 
One Solution to Wireless Router RFI  
by YI9VCQ on August 17, 2005 Mail this to a friend!
One solution is to make sure the cable modem and wireless router are on a different AC supply circuit. My modem and wireless AP are located all the way on the other end of the house back home. If you can't move your HF antennas, then move your AP.


73,

Korey
YI9VCQ/KA5VCQ
 
RE: One Solution to Wireless Router RFI  
by YI9VCQ on August 17, 2005 Mail this to a friend!
If you're surfing the net while next to your rig, then it is most likely the computer/laptop making the RFI.

My laptop loves to "sing" to my HF rig. Funny thing is that the noise goes down considerably when I plug my USB hub into it. I guess the RF goes a different path HI HI!

73,

Korey YI9VCQ/KA5VCQ
 
RE: RFI to aDSL modem  
by WA3KYY on August 17, 2005 Mail this to a friend!
You are probably getting direct ingress of the fundamental into the modem. There is no RF shielding in the cases. I used to have a Westel aDSL modem that did the same thing on 80M when I ran more than 10W of power.

When Verizon offered fiber in place of aDSL I switched and no longer have any problems when transmitting on any band.

You might try some method of providing RF shielding. A faraday cage might work with the modem inside with ferrites on all cables entering the cage. Lining the case with aluminum foil bonded to the groundplane of the citcuit board is another option.

But first contact your ISP or whoever provided the aDSL modem and see if they have a model that is not susceptible to RF interfernce at amateur frequencies.

73,
Mike WA3KYY

 
RE: RFI to aDSL modem  
by WA6BFH on August 17, 2005 Mail this to a friend!

Back in the days that I was running around dealing with these thankless issues for the ARRL, I ran into an interesting fellow. This guy did compliance certification for electronic devices imported into our country.

Our discussion topic was the prevailing problems that I dealt with involving interference to VCRs from the Ham next door (the guy with those big antennas). He showed me the filtering network area that was provided on the circuit board behind the playback head. No components were populated in the circuit board for this filter.

I asked him how then he could allow this into the country? His answer was, these are allowed this way in our country -- its only Europe or Japan that insists on the installation of the filter!
 
One Solution to Wireless Router RFI  
by WA1RNE on August 17, 2005 Mail this to a friend!
BTW, forgot to mention what might be the more "obvious" issue:

The power supply may be defective.


I use a DI-624 with probably the same power supply and I have no problems with RFI.
 
RFI comes from ethernet, not just from power suppl  
by KF6IIU on August 17, 2005 Mail this to a friend!
Linksys BEFW11S4, rfi comes from the ethernet cables attached to it, not from the power supply. Ferrite beads in the ethernet cables help considerably.

Some ethernet chipsets are really bad. I have an Intel mobo in a PC at home and I can pick up the birdies from the built-in 100baseT interface two blocks away. The interface does not radiate when the network link is down, so I use a PCI card for the ethernet.

I have a bunch of old 10Mb10baseT cards I've dumster dived over the years. They are all quiet. Could be the older 10MB chipsets are quieter than the newer 100Mb and gigabit ones.
 
RE: RFI comes from ethernet, not just from power s  
by KC2MMI on August 18, 2005 Mail this to a friend!
<<Wired or wireless [routers]- they both generally use switching power supplies.>>

Interesting. I've only seen them using common el cheapo wall warts with a transformer in them.

I went through some of this with a Linksys BEFSR41 last year, it made RFI/TVI like a squealing pig. No one was interested in it--including the FCC. There was no RFI shielding inside the router, which had a plastic case, except the metal socket covers for the RJ45 cables. No noise went out on the enet cables themselves, and torroids on the power supply cable did nothing. The interference was being radiated from the router itself.

On the other hand my old Westell DSL bridge, and new Westell WiFi router/bridge, are both RFI-silent. And all use plain wall warts.

I don't think this can be blamed on any one technology, it's that old case of the mass market demanding cheaper prices--and getting exactly, and only, that.

I did see one company on the web selling "RFI shielding spray paint", literally spray paint with nickel-coated copper particles in it to form a bright shiny silver metallic blocking layer on plastic enclosures that are RFI problems. Interesting concept, although a full aluminum foil wrap still didn't stop my little piggie.
 
RE: RFI comes from ethernet, not just from power s  
by AA4PB on August 19, 2005 Mail this to a friend!
I use a LinkSys BEFSR41 mounted on the wall just the other side of my shack and haven't had any RFI problems. Perhaps there have been some design changes since I purchased mine.

If the wall wart only contains a transformer in it then there is a regulator of some sort inside the unit; perhaps linear, perhaps switching. My point was that using a wired router vs. a wireless doesn't reduce the odds of you experiencing RFI. The problem generally comes from a switching power supply or some other digital noise radiated from the unit rather from the RF circuits in a wireless router. In fact, a wired router is probably more likely to create RFI problems because the RFI can be conducted and radiated by the long CAT5 cable runs.

In my work, switching regulators seems to be the #1 source of RFI problems. It is seldom the other digital circuitry. The switching regulator RFI seems to peak on the low end of the AM broadcast band. A $10 AM radio makes an excellent detector.

The bottom line is that I wouldn't let the RFI issue be the determining factor of whether I used a wired or a wireless router.
 
RE: One Solution to Wireless Router RFI  
by KC2MMI on August 19, 2005 Mail this to a friend!
<If the wall wart only contains a transformer in it then there is a regulator of some sort inside the unit; perhaps linear, perhaps switching.>
Not at all. The plain ones are AC-to-AC, the fancy ones are *un*regulated AC-to-DC using only one filter capacitor and two diodes. Really crude and cheap because cheap is what they need. Any design change requires the entire supply to be resubmitted for UL certification, which can be a $50,000 process from what I've been told.


<<My point was that using a wired router vs. a wireless doesn't reduce the odds of you experiencing RFI. >> Point taklen and totally agreed on! My wireless router is way quieter than than the wired one was.

<<The problem generally comes from a switching power supply or some other digital noise radiated from the unit rather from the RF circuits in a wireless router>>
Yes and no. Again, there is no switching power supply. They can't afford one at the price these sell for. A typical switching power supply for a cell phone sells as a, what? $40 accessory? Sometimes given away free in bundles, like the phones, but typically a $20-40 item when sold. There's no margin in the price of a $30 router to include that. The RF circuits in the router are also not usually the problem. Rather, it is a well-known problem that CPU's emit loads of RFI. There is a computer in every one of those routers (they are switching computers, after all) and unless that CPU has been properly designed, filtered, and SHIELDED in a METAL enclosure...the odds are it will emit RFI. That's why there are FCC ClassA and ClassB (and now ClassC) regulations that these routers must be certified in compliance with.
Some, like my Linksys, simply could not pass certification. I'm convinced someone fudged it, lied outright, or changed the design afterwards. But most--even if they are able to pass the stronger ClassB "home" compliance, still emit enough RFI to ruin reception on TV sets, etc. that have an antenna in the same room. And that's allowed--by the FCC. The limits are simply not high enough.
A lot of gear exceeds the standards, has shielded CPU's, good filtering, etc. A lot just doesn't. It's a matter of price and profit.
 
RE: One Solution to Wireless Router RFI  
by AA4PB on August 19, 2005 Mail this to a friend!
I can assure you that the ICs in the router are not running off raw AC or unregulated DC. If the wall wart does not contain a regulator then there are one or more regulators inside the router box - probably linear 3-terminal regulator ICs.

I make a living designing microprocessor based stuff so I understand about the noise that can be generated by the digital circuits. I also know that when there is a switching power supply involved it will usually generate 90% of the RFI and will be the most difficult to tame - primarily because it is dealing with much higher voltages than the digital logic circuits. Switching RFI is usually easy to identify because it is low frequency, generally peaking at the low end of the BC band around 600kHz.
 
RE: One Solution to Wireless Router RFI  
by KC2MMI on August 19, 2005 Mail this to a friend!
<<I can assure you that the ICs in the router are not running off raw AC or unregulated DC. >>
I didn't say they did, and certainly didn't imply it. Most of the wall warts are very crudely regulated by transformer saturation. A 9VDC wall wart typically puts out about 12VDC under no load, and promptly crumps down to 9VDC under the load it was designed and matched for.

<<If the wall wart does not contain a regulator then there are one or more regulators inside the router box - probably linear 3-terminal regulator ICs. >>
Could very well be. The 3-pin regulator chips I've worked with (78xx 79xx etc.) haven't had any RFI/EMI problems for me, so I wouldn't blame regulator circuits in the routers, either. On the other hand, the CPU's are known to be excellent RF sources, in the MHz range based around their clock cycle speed.

I'll accept your vocational expertise, although obviously some boxes have been built by folks who don't know their stuff. I never debated that switching power supplies make noise--but I stick to the statement that switching supplies are simply not used in most of the home routers, because they are simply too expensive to be used in them. I don't know what you design, but in the mass market for $20-40 home devices, "cheap" is the #1 design parameter, and the accountants make the engineering decisions. Not the designers.

Switching supply? Sure, my computer has one, my laptop has one...Try to buy one for under $50, outside of the surplus/scrap market. (Not counting the extremely low power ones sold for $25-45 for cell phones.)


 
RE: One Solution to Wireless Router RFI  
by AA4PB on August 20, 2005 Mail this to a friend!
Okay, I had to go look. My LinkSys Cable/DSL router power supply unit has "Switching Supply" written right on the label. My DSL modem supply is switching as well. It has 3 output voltages, +12V, +5V, and +3.5V. My LinkSys wireless access point is the only one with a true wall wart (plugs directly into the outlet with no cord). It is marked output +5V at 500mA. Based on the RF hash on an AM BC radio placed next to it I expect it is also a switcher (but I could be wrong on that one). I think switching power supplies are becoming much more prevelent than you think - even on inexpensive consumer products. Don't forget, these companies are purchasing power supplies in some very large quantities and will be paying much less than you or I would. Switchers also have the benefit that they are not so sensitive to input voltage or frequency so the same unit can be used in different countries without modification. That's also a cost benefit to the manufacturers.

The originator of the thread obviously has a switcher because he replaced it with a linear to get rid of the noise.
 
RE: One Solution to Wireless Router RFI  
by VE3TMT on August 20, 2005 Mail this to a friend!
I have two RFI issues, first is the switching supply in the TV upstairs. I have installed a toggle switch on the rear panel to save me from unplugging it every time I want to operate HF. When it is plugged into the AC socket the power supply generates S9+ noise on every band from 160-20m. My second problem, not yet resolved is RFI from my cable modem. The signals on my 850 seem to be in sync with the flashing of the LED's on the modem. Not sure if it is the LED's causing the RFI or the data transfers that correspond to the LED's. Still looking for answers on that one.

Max

max_ve3tmt (at) yahoo.ca
 
RE: One Solution to Wireless Router RFI  
by W9AC on August 21, 2005 Mail this to a friend!
Floyd's solution is a good one. Switching supplies should be replaced by linear types at every reasonable opportunity. The only external switch-mode supply I would ever trust is made by Lambda.

Like K8AC, I have now battled two switch mode supply problems. Last year, I found the power supply on my Linksys 8-port wired router was spraying hash all over the 40M band. That router has since been replaced by a commercial rack-mount Netgear router with metal case and internal switching power supply.

I used a portable SWBC receiver to quickly scan the entire HF spectrum and with the aide of the telescoping antenna, I localized the noise source very quickly. I just move the antenna like a wand over various places of suspect and when you're near, you really know it. Just last week, I localized a problem with another switch-mode power supply -- this time it was the powered sub-woofer on my home theatre system.

Paul, W9AC


 
One Solution to Wireless Router RFI  
by K9YC on August 22, 2005 Mail this to a friend!
Over the past three years, I've been doing considerable research on the use of ferrites to suppress RFI on the ham bands. I've summarized my work in an applications note that is on my website as a pdf. While it is specifically written for sound contractors, hams can benefit greatly from the information. There's also a pdf of a presentation that I did for my ham club.

http://audiosystemsgroup.com/publish

Click on the links to get the pdf's.

I also strongly suggest that you study the material on "the pin 1 problem." This is a major cause of RFI to and from our radios, to and from consumer gear.

The applications note adddresses the common mode QRM that is generated by Ethernet gear because the output transformers lack a Faraday shield. Ferrite chokes attneuate this QRM a lot. The catch is that once you kill your own stuff you'll hear your neighbors, each of which is running on a slightly different clock, hopefully weaker than yours.

If you want to ask questions about this, contact me directly. It's not likely that I'll come back here to read replies.

73,

Jim Brown K9YC
k9yc@audiosystemsgroup.com
 
One Solution to Wireless Router RFI  
by W6OPO on August 24, 2005 Mail this to a friend!
I was using a Linksys BEFW?? 4-port wired router (there was no wireless) I bought in 1998. It generated carriers on 14.150, 14.090, every 60Kc up and down the band. Noise was NOT from the wall-wart but from the either net cables.

So 2-months ago I bought a Linksys WRT54G wireless router and found the carriers were still there, coming from the either net cable between the DSL modem and the router.

I then removed the router and ran the either net cable from the DSL modem directly to the PC, the carriers were back again! Disconnect the either net cable and the carriers disappeared. Plug the cable in and the carriers were back.

I deduce from this test that the basic either net signalling produces these carriers.

BTW - I used CAT5 cable which you know has no sheilding. With the plastic boxes and wall-warts isolating the router and DSL modem from ground how could one ground a sheiled cable?
 
RE: One Solution to Wireless Router RFI  
by AA4PB on August 25, 2005 Mail this to a friend!
It sounds like your problem may be in the DSL modem. How long is the cable between the modem and the router? You probably want to keep it as short as possible (mine is 1-foot). You could try some ferrites on the cable close to the modem.

It is quite possible that the RFI is being generated internally in the modem and simply being conducted out the CAT5 cable due to poor isolation. I have CAT5 passing right behind my rig and don't have any RFI so I doubt that your RFI source is actually the eithernet signals on the CAT5. CAT5 uses a balanced, twisted pair so signals should not be radiated very far from it.

Also consider the possibility that although the RFI is related to the CAT5 connection, it may be feeding back out the phone connection which would give it a much longer "antenna". Some ferrites on the phone cable might help.

Worst case you might want to consider upgrading the DSL modem to one of the combined DSL Modem/Wireless router units which would eliminate your CAT5 connections completely.
 
RE: One Solution to Wireless Router RFI  
by K0SF on October 15, 2005 Mail this to a friend!
Mark:

I have the same problem. I wound a large FT240 toroid on the phone cord and that eliminated the 75m problem, but I still knock it out on 160m. I ordered additional high permeability ferrite toroids so that I can isolate the power and ethernet cable. I'll keep you informed of the the results. Have you found a fix yet ?
 
Router RFI solved!  
by VA3DK on December 13, 2005 Mail this to a friend!
The forum posts were helpful to me and I too found the router RFI was following my LAN cabling.

I tested Netgear WGR614, DLink DI514, SMC SMC7008 routers and found all had lots of RFI!!

I stopped router RFI from propagating via my LAN cables by installing a commercial 10BaseT hub Antipodes model AI-505. My LAN cables all connect to the hub ports then I connect to the router via a hub port.

This dropped the LAN speed from 100 to 10,..:-(... but no RFI now... :-)...!

Does anyone have RFI experience with Linksys Wireless routers? My Linksys Etherfast 10/100 Workgroup switch is RFI quiet, how about their wireless routers? I would consider replacing the wireless router with a Linksys or replacing the hub with another Linksys Etherfast to regain the faster LAN speed.

73's
Dave
 
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