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Author Topic: Reducing RFI from ethernet routers  (Read 1979 times)
WA2ISE
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Posts: 144




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« on: August 23, 2014, 04:47:39 PM »

Many ethernet routers and switches have internal switch mode buck voltage reducers/regulators.  These circuits can cause a fair amount of trash to pollute the AM broadcast band and HF.  I found that using one of those dual winding RFI coils salvaged from computer, VCR, DVD player and such switching power supplies can reduce the RFI way down.  You need to put it inside the router housing (or really close, in back) and have the DC power from its wall wart go thru this dual coil.  Look at how it was hooked up in the switching power supply you scrapped and see where the inputs and where the outputs are taken.  It won't matter if you feed the outputs and get power from the inputs, but you want to avoid getting the two sections out of phase.  A 0.1uF cap across the wall wart side of this dual coil also should help. 

You don't need to worry about RFI getting out along the ethernet cables, as most if not all ethernet jacks have small isolation transformers associated with them.  These provide around 1000VDC HiPot isolation, and have maybe a dozen picofarads capacitive coupling, common mode around -25dB in HF.
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WA2ISE
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« Reply #1 on: August 23, 2014, 07:07:20 PM »


The added RFI dual coil is in the center of the board.  The big filter cap is not related to the RFI reduction (it is associated with a diode so I could use a source of 8VAC to power this switch).
« Last Edit: August 23, 2014, 07:12:17 PM by WA2ISE » Logged
K1CJS
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« Reply #2 on: August 23, 2014, 08:58:22 PM »

Another thing that can be done is very simply use a quality power supply in place of the wall wart that all too many of these modems and routers come with.  Many of the wall warts in use are noisy as heck--sometimes not to the device they power, but often to electronics in the same house.
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N1UK
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« Reply #3 on: August 24, 2014, 09:05:54 AM »

Quote
Another thing that can be done is very simply use a quality power supply in place of the wall wart that all too many of these modems and routers come with

Agreed, if the wall wart feels "very light" then they are probably missing the required common mode and differential chokes and will be a major source of rfi.   I have had to substitute a couple of very bad supplies with the stock of old transformer wall warts that I keep on stock.

Look for a Class 2 Transformer supply.


Mark N1UK
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KD0REQ
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« Reply #4 on: August 27, 2014, 11:46:54 AM »

and also look for a metal case with a ground lug on it for ether switches.  Netgear still makes some, and the price is right.
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ZENKI
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« Reply #5 on: August 30, 2014, 06:22:28 PM »

Just drop the speed in the Ethernet controller, that can generally get rid of most of the bad birdies. Very  few people need the full speed of their  ethernet interface.

Change the speed to 10mbits half duplex and you can minimize the birdies. You can find this in the adapter settings in "speed and duplex settings"

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KD0REQ
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« Reply #6 on: September 03, 2014, 09:58:58 AM »

in these days of streaming and heavy use, I think 10/half is as silly a speed as the original 3 mbps Ethernet was.  you can stay on 100/full and have no issues if you have a decent bunch of equipment.  wrapping four or five turns of cat-5 around a big toroid from an old PC power supply should knock down any interference without killing the transmission on a segment.

I have a netgear 5-port sitting right behind the rig in the Ham Cave, 40 feet under the dipoles, and no problems.  the switch is shielded and the wall wart is quiet.  my feed from the house has one clip-over ferrite on it and is run in EMT to the jack plate.  there is an old Belkin wifi port sitting on top of the box behind the rig, and there is no cross-interference.

cheap noisy junk should be returned if new, and tossed if old.  there is plenty of good equipment out there that won't drive you nuts, at market prices.  beware the price way below expectations, those are the folks who left all the care out, and the FCC cert is probably fake.
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KK5DR
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« Reply #7 on: September 06, 2014, 07:14:31 AM »

I've had at least four types and brands of routers in my home. None are ever located in the same area as my radio gear. They are always separated by at least 50 feet. Thus far, I have not had any RFI from them, or to them.
Proximity is a major factor.
A router sitting 2feet from your HF rig, set to full power maybe a problem for the HF radio. As well as the HF radio transmitting at full power my cause trouble for the router as well in that close proximity.
Things to think about when installing the router in your home.
I've had expensive brands, and super cheap brands, it didn't seem to matter, as long as it was a good distance from the radio room.
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