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Re: [RFI] RF getting into 4-port wirelss router.

To: rfi@contesting.com
Subject: Re: [RFI] RF getting into 4-port wirelss router.
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Wed, 14 Jan 2015 00:34:33 -0500
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 1/12/2015 11:49 PM, KD7JYK DM09 wrote:
:I suppose if you're an expert at everything, there's no reason to try to
: help.

I know of no one who is an expert on everything. Actually I know a number of knowledgeable people, but no experts.

I'll repeat what I said before (as did several others) and ask some questions. The remedies of RFI suppression have been pretty well covered. Jim's tutorial does an excellent job of showing how to suppress RF that gets in the line.

*If these remedies have not worked, it's time to stop and look for reasons!*

Is the problem really RF? If RF, it almost has to be common mode. There has to be a reason why this particular setup is so prone to problems. It's not just RF getting in, it's RF (Or Something. It could be AC, or DC as well when the equipment is powered up) at a magnitude that is frying the equipment. It again, (if nothing mentioned previously has been overlooked) almost has to be something we'd not expect as the regular approaches have not worked. Jim's air core resonant coil should be effective at removing a specific narrow band of frequencies. Get too many, or too few turns and they don't do much. (Old terms and thinking die hard) while the chokes should suppress a wide range of frequencies. They are wide band, but switching power supply frequencies take more turns than the ham bands. OTOH the Power supplies can have frequencies well up into the ham bands

Remember the RF getting into the house wiring and tripping GFIs. Might this be a key?
Knob and Tube wiring in some areas.

IF this is RF getting into the CAT5 why aren't the failures almost immediate? (as has been noted previously)
Loads connected and disconnected?

Are the failures temperature, or weather related.

Knob and tube. I lived in a house like that many years ago. Normally, "Knob and Tube" is only two wires with no ground wire so the outlets would not have a proper ground even if they do have a ground. Knob and Tube use only two pin sockets.. IE, they won't work with GFIs and should never be part of a circuit that has GFIs. IE an extension. Running a separate ground wire to outlets on knob and tube is begging for problems and can be dangerous. A house with ham gear and computers should have the K&T replaced and removed as soon as possible.

What is different about this setup besides the Knob and Tube? IIRC he has a vertical that's fairly close. Do any of the radials come close to the CAT5? Is the equipment "earthed" at each end? Are the coax and radials "earthed" at the base of the vertical. If so, are all connections secure? Is the CAT5 a resonant length? Is there something common between the rig and network?
I keep thinking Knob and Tube.

If removing the CAT5 eliminates the problem, disconnect it and measure voltages to ground while transmitting. Borrow an O-scope or spectrum analyzer, but expect abnormally high voltages. If you are not familiar, borrow the owner of the equipment too. That way you shouldn't be responsible. A quick and check would be to disconnect the CAT5 and put an NE51 between it and ground to see if it really is RF of substantial voltage.

It would help to know the layout of the entire "wired" network. I lieu of a drawing a good description might help Are the other computers still connected when the router/switch are disconnected? Does your local ham club have an RFI group, or individuals well versed in hunting down problems? If available make generous use of local brain power.

A knowledgeable person, or persons present can do a lot more, quickly than we can here.

I will relate a problem I had a while back, I had fried two relatively expensive duoband (VHF/UHF) verticals which in turn took out some expensive finals. The problem turned out to be a combination of a power supply and grounding problem which all agreed shouldn't happen. I'm still not sure about it, but with all grounds in place, its been working for some time.

Knob and Tube...That is the main difference between this house and most with ham stations and computers. BTW At the risk of dating myself, when I was a kid, Knob and Tube was not uncommon.

73

Roger (K8RI)


Well, not on RFI since the OM asked for help...  I would start by making
chokes out of all wires entering the device.  Wrap a half-dozen turns around
your hand in a loop four to five inches across and secure with plastic ties.
See what happens, try a few more or few less turns if the problem persists.

I did this with a monitor that eliminated all radio usage 135' from the
antenna.  When I was done, RFI was limited to roughly three inches.  I used
spectrum analysis software as I wound my chokes and monitored the RFI with
my primary radio and could see it disappear on the monitor and audibly as I
made the loops.  Simple, effective, free, been in use about seven years now.

Kurt

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