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Author Topic: What routers are Ham's using that are RFI FREE  (Read 5654 times)
K0KAD
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Posts: 7




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« on: November 16, 2012, 10:06:51 PM »

Hello everyone!  I have been bitten by the router RFI bug.  It is wrecking my world of VHF as we speak!!!  I have tried to shield the router and that didn't work at all.  I pulled that thing apart and mounted it in a metal enclosure.  I then powered the thing from a sealed lead acid battery that I precharged.  So with those things out maybe someone out here can lend me their recent experiences to helping me out with my RFI.  Yes I have searched the forums and found some but I am looking for some that have wireless G at minimum hopefully N only time will tell.  Some of the early routers that were in metal frames were very well shielded but were not up to today's standards of communications.
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K0KAD
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Posts: 7




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« Reply #1 on: November 17, 2012, 12:23:54 AM »

Just as a short note here I did end up trying to replace my router with no luck.  Once replaced I got the exact same RFI on the exact same frequencies that I did before.  That to me is odd really would have thought it would have been a similar noise maybe but resonating on different frequencies.
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W9GB
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Posts: 2600




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« Reply #2 on: November 17, 2012, 05:19:51 AM »

Often, the issue is the SMPS used to power these home network routers OR
the UTP cable being used that are connected to the router.
--
I use Linksys/Cisco home network equipment.  
Linksys use to ship snap-on ferrite cores for some of their early models to address RFI issues.

BIG BOX stores sell junk and consumer quality,
A discerning eye is required for bargain purchases -- OR --
you end up buying factory QA rejects and problems in your radio shack.


Sub-standard UTP cabling (not true Category 5e)
Small SMPS power units - RFI generators
Improper installs
Poor modular (RJ-45) connector terminations
Network Cabling parallel to power or audio cabling
« Last Edit: November 17, 2012, 05:25:39 AM by W9GB » Logged
W8JX
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Posts: 5489




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« Reply #3 on: November 17, 2012, 06:08:25 AM »

I have had good luck with NetGear routers. Currently using a WNR 2000 v3 which can be had for under 50 bucks. Before that I used a WNDR 3000 dual band router that gave up ghost after 3 years of hard use.  It is a B/G/N router and I got it because it is designed to be used as a access point or repeater which I will use later when I upgrade router again. By design N is backward compatible with G and B. One must remember that when you use N you use more of spectrum and a more complex modulation too which in "theory" could create more possible RFI.
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Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
K0IZ
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Posts: 737




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« Reply #4 on: November 17, 2012, 02:41:08 PM »

I have been using a LInksys router, had RFI at about 61Khz intervals, 14.212 was typical freq.  I changed to NetGear, and have basically same RFI at same frequencies.  I have clamp on ferrites on every Cat5e cable going to router and wall wart.  Changed switching wall wart to older transformer type.  Nothing really helped.  I believe the Cat5 cables are radiating the RFI.  When I switch antennas, the RFI changes.  Level of RFI is not real bad, perhaps S2 or so on my K3 at 14.212.   Also have a Cisco 8 port switch.  Also generates same 61Khz RFI!  I have learned to live with it.
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KF5RUK
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« Reply #5 on: November 21, 2012, 05:32:39 AM »

Please forgive the Telecom 101, but I think everyone might be misunderstand the way in which Unshielded Twisted Pair or U.T.P. cable works. The original ideas behind the need to reject noise in the minds of early Telecom Engineers was the rejection of the most fundamental noise creator that in many cases 60Hz AC which was on the same pole or at least many times crossed their cables at intersections. 

The effect the twisting of the pairs has is that the induced noise is hopefully out of phase on each conductor, and when used to input a differential input on an Audio Amplifier the noise or induced 60Hz would be out of phase and cancel itself out thus producing no output on the other side of the amplifier. Cat 5e for Ethernet depends on the same cancelling out effect to a differential driver as this is how the layer 1 works since it uses a Manchester Encoding Technique. Various digital encoding schema also take advantage of this effect when they split data into an I & Q data stream as well as an I & Q inverted stream called I & Q NOT for logical NOT. None of these will have any effects on the RFI, and I also suspect that there could possibly exist coupling, but most better routers have optically isolated inputs to prevent DC Coupling or inadvertently forming ground loops in the systems interconnected by the router.

If the 61KHz is being radiated by the cabling them possibly upgrading to a CAT 6 with a grounded shield would prevent some retransmission if that is even happening. I suspect their is no potential traveling down the cables so I would advise against the expense of the CAT 6 cabling that would provide a shield. The 61KHz sounds interestingly like an "by-product" of switching SCR's that are common in UPS's.  Is it at all possible that an UPS is generating the noise? If not then we are back to some kind of DC-DC Convertor that almost always uses a really cheaper method of DC to DC conversion that uses a DC to AC conversion using again SCR's then using a small step up or down common by winding the secondaries of transformers differently for the different voltages, and then full wave rectification to the desired DC Voltage. The SCR's commonly are gated or switched by a Pulse Width Modulated technique gating the SCR's with this higher frequency waveform, and again this is very common in UPS's but unlike the cheaper Cisco / Linksys junk the UPS's manufactures usually include very expensive filtering to eliminate all of the AC ripple common on the output of all power supplies.

I could be totally off base here ,but a few checks with either Frequency Selective Voltmeter or an O-Scope would be very helpful. The fact many people are seeing the same thing , and the frequency makes me suspect a power supply design that might be a common sub-assembly that all vendors OEM from an outside vendor which is using Switching SCR's. I would suggest looking at the cables even the Grounds like in the AC Power Cord.

The commercial 100KW UPS I worked on 30 years ago used 100KHz as the Switching Gate Frequency so I would be real interested in knowing the results if anyone can do the measurements with an O-Scope, and if you could do a storage scope you would see the noise is actually a series of Bursts on and off if it is the problem I was proposing someone investigate with a scope.

73
Elmer
KF5RUK
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K3DCW
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Posts: 182




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« Reply #6 on: November 22, 2012, 10:11:33 AM »

Hello everyone!  I have been bitten by the router RFI bug.  It is wrecking my world of VHF as we speak!!!  I have tried to shield the router and that didn't work at all.  I pulled that thing apart and mounted it in a metal enclosure.  I then powered the thing from a sealed lead acid battery that I precharged.  So with those things out maybe someone out here can lend me their recent experiences to helping me out with my RFI.  Yes I have searched the forums and found some but I am looking for some that have wireless G at minimum hopefully N only time will tell.  Some of the early routers that were in metal frames were very well shielded but were not up to today's standards of communications.

Either of the Apple routers, but specifically the AirPort Extreme: http://www.apple.com/airportextreme/  It is a VERY quiet (RFI) router.

And, no, you don't need a Mac to use it.  You can download the AirPort software to Windows and get it running quickly.

73

Dave
K3DCW
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W5ZL
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Posts: 11




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« Reply #7 on: November 22, 2012, 04:33:11 PM »

At my installation, I have a a Netgear wireless router with two devices attached to it by CAT-5 cable about 5 feet each to two different printer devices which are on the Network.  On the Wireless side of the Wireless Router, I have 4 computers which use it, with two of them in my Ham Shack and I haven't experienced and RFI problems from it.  The current configuration in my Shack has been static over the past three years with 2 HF Transceivers, 4 VHF/UFH Transceivers, 3 HF and 1 6M Amplifier and associated power supplies, antenna tuners, etc. and associated Ham equipment.  The Wireless Route employeed here is the NETGEAR 54 Mpbs Wireless Router Model WGR614 v6; 54 Mbps, 2.4 GHz, 802.11.  So far, I have been very lucky that the Local LAN, both the Wired Network of printers and the Wireless LAN of the 4 PCs.  Hope this may be of some help to those that are having RFI Problems with their home networks.
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K0KAD
Member

Posts: 7




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« Reply #8 on: November 24, 2012, 08:35:23 PM »

Just to update everyone on my steps I have taken here...

1) Replaced all cabling with STP (Shielded Twisted Pair).  Although I suspect now since I dont have a Gbit router that I dont have the metal tabs on the sides of the jacks to make contact with the shielded plugs that I will have to change that next, cause the shields are pretty useless without the connection to ground on the units.  Smiley

2)  Removed all unnecessary items from the system.  (I dont use the ondemand features of my Satellite system so I unhooked the internet injector system. etc.)

3)  I added ferrite snap on beads to the antenna feedline on the roof and at the back of the radio. 2x each end

I did notice after those things were done that I had a small shift.  I use VHF here in my room and the noise was on 147.150mhz, 147.215, 147.340 etc but before those things were done it was on 147.155, 147.220, 147.345 etc.

The next project is in the next day or two I will be moving my router, cable modem, magicJack phone out to the garage and I will piping in via STP a hardwired connection to the computer in the other room.  Most of the computers use wireless so hopefully that will work and cure the problem.
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KC4MOP
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Posts: 729




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« Reply #9 on: December 02, 2012, 03:38:44 AM »

A lot of good thoughts here. I have had good success with the Netgear routers in metal cabinets. And CAT 5 cable makes an excellent antenna for the digital garbage contained in a poorly constructed router.
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W8JX
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Posts: 5489




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« Reply #10 on: December 02, 2012, 08:15:44 AM »

Go wireless and eliminate the cat 5 antenna wire.
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Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
WA7NCL
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Posts: 625




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« Reply #11 on: December 17, 2012, 01:16:23 PM »

The guy with the 61KHz has a switching power supply with common mode radiation connected to his router or the network cabling somewhere.  I've never seen the ethernet traffic produce RFI on a good cable.

Another thing to consider, is the network has many other computers and displays hooked to it.  Any of the attached computers or their displays could be producing RFI that couples to the Ethernet cabling as common mode.

Most of the time RFI comes from the switching power supplies of the router.  Most routers run on 5V or 8V or up to 12V.  You can look on the device and the power recepticle will say what it runs on.  Then find an old style linear power supply and attach to it.  Quite often that fixes it.

I have seen TVI to cable boxes and TVs from wireless routers.  Then you need to add some clip on ferrites to the ethernet cables because the wireless router is emmitting common mode on the cables.

When ever I hear the "I changed everything and nothing works", it usually means you misdiagnosed the source of the EMI and everything you changed had nothing to do with the cause.  Thats why nothing works.
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K0IZ
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Posts: 737




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« Reply #12 on: December 17, 2012, 05:43:43 PM »

I have the 61Khz problem and I don't have any switching power supplies to the routers or switches.  Same interference with Netgear and Linksys routers.  Also with Cisco switches.  I only use old style transformer type power supplies.  And not coming from any other wall warts in house:  If I disconnect all cat5 cables from router output, noise stops.  Adding one cable, no matter which one, noise starts.  Even if other end of that Cat5 cable is connected to nothing.  So obviously internal to router (or switch), and apparently being radiated by the cable.  And not from anything else in house.  I also added multiple clamp on ferrites to all cat5 cables, not any difference I could detect.
« Last Edit: December 17, 2012, 05:47:25 PM by K0IZ » Logged
W4MMR
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Posts: 7




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« Reply #13 on: December 22, 2012, 05:34:23 AM »

Here are my two cents concerning EMI//RFI based upon my experience just for your information.

I doubt there any routers that are RFI free out there, but I agree that the quality or lower impact the device has upon its environment may be directly proportional to cost i.e. commercial routers may be less noisy and expensive versus the ones we can buy at BestBuy made for a house which are cheap and radiate a lot and may be affected from your signals as well.  The difference between these devices is the specification that they are tested against of which there are as many as their are blades of grass in the universe.

Devices are tested to particular standards for EMI/EMC conducted and radiated emissions of which are based upon their intended end usage.  As an example, devices used in the marine environment have specific requirements for EMI transmission within the areas of frequencies that other devices operate such as marine radio bands.  A typical specification is the ABYC P-24-07 which indicates that between 156MHz and 165MHz a device can not radiate more than 24 uV/m of energy, protecting the marine VHF band.  There are other levels within that specification between 150kHz and 30MHz, also, although the radiated levels are not as low as for the VHF.  The ABYC spec is primarily used with respect to marine radio interference and I doubt that routers are tested against that standard.  So routers we purchase for cheap may not be tested with reference to ham radio frequency spectrum so unless you can see the results and know the standards said routers are tested to--most likely relates to other commercial devices on the premise of which ham radio gear most likely is not on the list, then you have to resort to trial and error to reduce their effects on your radios - a spectrum analyzer is handy for experimentation as long as you know what the noise level is of the environment and work from that reference.  Not sure if those can be found at a hamfest or not Wink.

Just so you know, every electronic device that operates in automotive, marine, and medical environments are tested for EMI/RFI to any host of governing bodies with respect to specifications.  Specifications range from those developed by automotive suppliers, SAE, IEC, IEEE, DOD, and others with most of these referencing back to some larger regulatory standard such as IEC.  I work with many of these and part of the challenge is to find one that works with all of them within my industry of transportation.

Radiated emissions are influenced by many things and primarily with anything of course that "vibrates" such as power regulators taking Vbat down to 3.3 or 5VDC levels.  A typical fix for a noisy regulator on the board level may involve moving components away from noise producing devices and/or adding very tiny chokes on conductors or adding guard traces to the board.  Placement of the devices with respect to other pieces of hardware (and its wires) that may be affected by it can be an easy way to reduce a radiating devices effects (remember those notifications on the back of electronic devices?) plus one can add chokes to lines, reduce lengths, and all that.  Even how the wires are bundled outside the device affect how much/efficient it can radiate.

mark
« Last Edit: December 22, 2012, 05:36:55 AM by W4MMR » Logged
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