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Author Topic: RFI on 20m from router  (Read 3037 times)
N9LEA
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Posts: 10




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« on: April 15, 2007, 05:03:20 PM »

Help!
 
I just put my shack back together again after a 4 year hiatus (moved to new house, never got around to it...).
 
It's an Icom IC-730 running on a 20m dipole with twinlead feedline.  The radio is in the basement and the antenna is in the attic.  The router is on the ground floor.
 
There's awful RFI and, not surprisingly, it's pretty much on 20m.  It makes the whole band unusable, with noise on the whole band and a particularly loud level around 14.200 or so.  After some messing around, I figured out that I can wipe out the RFI by killing power to a Hawking Technologies Wireless Router.   Then, I did more experimentation.  If I run the router with nothing attached (no input from the cable modem and no wired connections), it's pretty quiet.  I can even hold it right up to the radio and it isn't bad.   If I coil the line between the cable modem and the router, so that it's effectively a short cable, there's a little noise but it isn't bad.
 
As soon as I connect any of the Cat 5e to the back of the router to hook up to a machine that isn't wireless, I'm back to big time noise - S9+.  I can make it get a little better or worse (S5 at a minimum) by coiling the Cat 5e, and strangely can slightly modify the frequency of the extra loud part, but it's pretty much unusable.
 
So, I know I could probably buy a better router.  I could also probably go completely wireless.   But, I'd rather not do these things.
 
I'm trying to figure out some way to keep those cables from being antennas, which is what I assume is happening.  Any thoughts?  Are there better cables that can be purchased?  Would some sort of choke help?  How about tin foil?  Smiley
 
Thanks!
 
Jason, N9LEA
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KC4WMS
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« Reply #1 on: April 15, 2007, 06:05:58 PM »

Sounds like, being of the "geek" persuasion, I suggest you try stp ( shielded twisted pair ) cat5 cabling to see if it doesn't remedy your RFI. Yes they cost a few cents more but in many cases will eliminate the noise.

Good Luck & 73  de kc4wms with assistance from KC8PKR net admin. anora.org
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N9LEA
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« Reply #2 on: April 15, 2007, 08:02:01 PM »

I noticed that one of my lines is STP, though the others aren't.  I suppose it is bad if any leak.  If I hook up just the STP line, it is almost worse.

Can the shielding break on these cables?
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N3OX
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« Reply #3 on: April 16, 2007, 08:14:27 AM »

"Would some sort of choke help?"

Very possibly.  Ethernet twisted pair, even the unshielded stuff, is a good transmission line and shouldn't radiate unless it's got common mode currents on it, and it's possible that the equipment is causing common mode currents to flow... so some good HF-killing snap-on ferrites on the outside of the cable should help.  Try the good ones from DX Engineering or somewhere else that sells them particularly for HF suppression... the Radio Shack ones are better for VHF.

And, maybe the best advice I can give you, read this:

http://audiosystemsgroup.com/RFI-Ham.pdf

In particular, a tutorial on killing Ethernet hash starts on page 12, but I'd recommend reading the whole thing.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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« Reply #4 on: April 16, 2007, 12:18:40 PM »

Why not get a 2-foot CAT5 cable to connect the router to the modem (keep it short). You might also try some ferrite snap on beads (sized for CAT5 cable) at each end of the cable.
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Bob  AA4PB
Garrisonville, VA
N9LEA
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Posts: 10




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« Reply #5 on: April 16, 2007, 01:45:05 PM »

I have tried a very short cable connecting the router to the modem.  That cable doesn't seem to throw nearly as much noise as the ones that connect to the wired computers, though.  Those are killers.

Thanks!
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N9LEA
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« Reply #6 on: April 16, 2007, 06:14:57 PM »

Any clue whether these would be worth trying?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260107843558

They're a good deal, if they work.  I have no idea what a T-20 is and haven't had much luck looking it up.  Perhaps that's a bad sign.  Smiley
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N3OX
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« Reply #7 on: April 17, 2007, 01:09:32 PM »

Probably worth a gamble at less than a buck apiece.  They'd probably at least work as a VHF choke balun for some other project if they didn't kill your router noise.

The .pdf file referenced above has material type recommendations if you don't have luck with the eBay random beads.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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Posts: 14492




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« Reply #8 on: April 17, 2007, 07:00:49 PM »

I wonder if a switching supply or other digital noise is being conducted out the CAT5 cable. I've never experienced any RFI from the actual ethernet signals. If its conducted then some ferrites on the cables may help. You might also try ferrites on the power supply cables if its a switching type.
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Bob  AA4PB
Garrisonville, VA
AB0WR
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Posts: 77




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« Reply #9 on: April 26, 2007, 10:42:15 AM »

Doesn't shielded cat5e cable require the use of compatible jacks? I doubt if most residential use routers like this one have the special jacks to make use of the shielding. Without that you would have to extract the shields, tie them together and ground them at both ends. Not an easy task to do. You could easily just wind up with even worse radiation.

The hubs, switches, and routers that I have that make noise is from noise inside coupled to the external cables which then radiate it.

The only answer is to get different equipment or take the unit apart to see if shielding can be applied inside the unit.

tim ab0wr
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KF7CG
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« Reply #10 on: April 26, 2007, 11:33:04 AM »

From a former instrumentation specialist that has had to contend with much noise at all frequencies. Sheilded cables for data transmission should only have connnections to the sheild at one end.

Doing otherwise invites multi-point grounding with differences in noise voltages at the ends generating noise currents and making the situation worse. Sheilds can go a long way to creating ground loops if not properly grounded and applied.

KF7CG
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WA9PUL
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« Reply #11 on: May 02, 2007, 09:59:50 AM »

And if all else fails, ditch the Cat5 and go wireless.  That is what I did to cure similar issues. I had similar RFI problems throughout the HF spectrum.  Disconnecting all wired connections made things a LOT better.

It is also one less connection to worry about in the event of a lightning hit or power surge.  

Paul
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KB1THH
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Posts: 46




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« Reply #12 on: June 02, 2007, 12:46:17 PM »

Unsheilded twisted pairs all around for a RF free network. STP was given up a while ago for interferance reasons along with stray and unpradictable grounding problems leading to unwanted antenuation of stray signals, both AC, RF and spurious emissions of other support systems within a building. UTP fixes this problem by cancling out inductance by its cancilation and redundancy of ground and or sheild.


Back to the question at hand...
UTP cables all over
Ground your coax outside..

do fine
73 Jow
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KF4KQI
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« Reply #13 on: June 26, 2007, 07:30:09 PM »

I have a Hawking router... or "had" a Hawking, it did the same thing, my solution which seems to work great, is to to unplug it, and smash it with a sledge hammer, while running around in a circle yelling your call sign.  
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