RF causing Router/Router Extender/Flex 6500 to stop working on 40m

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  • Updated 5 months ago
I recently changed Internet providers and as part of the installation, they had to run new cable into my house.  So far, the only band that seems affected is 40m.  Here is what happens:  At 100 watts, there is no problem.  However, at 400 watts, the Router/Router extender stops communicating causing my Flex to lose its connection to my computer (they both connect to the RF extender via Ethernet cables.)  I need that set-up in order to be able to access the Flex via the Internet in anticipation of getting a Maestro.  I already put RF chokes on all the Ethernet cables with no change.  Would putting one or two chokes on the cable to the Internet modem hurt my Internet access?  I don't want to do anything stupid.  I'm open to suggestions.
Andy, k2oo
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Andrew Thall

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Posted 5 months ago

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Stan - VA7NF

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No problem adding additional torroids to any cable except fibre.  Are you aware the impedance increases by the square of the number of turns?  If you can make 3 turns on a bead it will have 9X the effect whereas two beads straight through is only 2X; this rule fails at VHF due to capacity between the turns but then you are at 7Mhz.
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Jeff / KI0KB

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I had a similar problem only on 20 meters at high power. I bought three sets of the DX Engineering network filters. I placed a set between the Flex and router, a set between the computer and router and a set between the router and a network switch that I run all of my ham network equipment. Problem solved. Prior to that multiple Toroids on multiple network cables did nothing to fix the problem.
Jeff Schwartz / KI0KB
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I switched to fibre from the router to the radio/PC and 95% of my RFI issues disappeared. 

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Martin Ewing AA6E

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You can try ferrite toroids on the power leads of your router as well.   It is possible that your new cable run is near resonance on 40M, so if you could put toroids on the cable somewhere in the middle of the run, that might help.  Also note that many ferrites (e.g. type 43) are optimized for higher frequency use and have less effect at 7 MHz. Type 61 might be a good choice.  See http://www.cwsbytemark.com/CatalogSheets/Ferrite_datasheet_oct06/FR_MATL.pdf for example.
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Gary NC3Z

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Skip the small clamp on beads, these are far superior and as noted the more turns through the better. You can put a lot of turns through these and get some pretty tremendous choking.

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The power leads are often the place where RF gets in, in addition to the Ethernet or mouse / keyboard leads. You’ve been running this setup before, so concentrate on the things that have moved/changed. The WiFi signal chain itself _should _be fine - neither Bluetooth nor WiFi devices themselves seem to be greatly affected by RF away from their operating frequency..

What really seems to work well are some of the binocular toroids (glue two tubular toroids together) with multiple turns thru them. That works well if you either have small connectors or can get the cable on the toroid before connectors. Of course you can always just get them large enough to pass the connectors on the end. It those long cable runs that are a pain and may force you to use split toroids.

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Andy.  Chokes should be installed at both ends of the ethernet cables as close to the devices as possible.  They must also be would correctly to work effectively.  If using clamp on type beads you may need several at each end.  You can buy large diameter clamps and wrap a few turns of ethernet cable though them if possible.  Using a large 2.4 inch diameter mix 31 ferrite core would be the best option with ethernet cable.  Take a look at the link below on how to wind them to get maximum choking impedance.  You should also place chokes on the DC power cables to your Internet routing gear.  DXEngineering also makes a special choke (DXE-ISO-PLUS) for ethernet cables.  They are a bit pricey but all the work is done for you. 

It would also be a good idea to place chokes at antenna feed points and antenna feed lines. 



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Gayle Lawson

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Ted VE3RTQ may have hit it, add some core to the router power line.

I agree with Gary NC3Z.  You can easily get 5 to 15 turns of Cat5/6 cable through one of these cores.  That will give you 1 to 5K ohms impedance at  7 MHz (depending on how many turns).  They cost about 5$ a piece from Mouser.  The cores are heavy, so plan on supporting them, I would not let them hang on the connector. 

If you use clamp on cores, get the ones with .5 or .75 inch holes, wind multiple turns as described by VA7NF's posting above.

DX Engineering has Ethernet  filters, but they cost $49 for a pair (check their catalog).

Gayle K0FLY 
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Ray Sylvester

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try a Collins style choke at the shack end of your 40 m antenna . simple to construct 8 turns of rg8x coax 8 inches in diameter taped together . it will decouple any stray rf on the shield of your transmit antenna
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Andrew Thall

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Firstly, I want to thank ALL the people who took the time to help me.  The solution turned out to be:  Relocate the internet modem and router and eliminate the RF Extender.  All is well.
Again, thanks to all.
Andy, k2oo
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Great that it worked out for you. Hopefully you can return the extender.
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Dan Trainor

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For future reference, these work good:  https://www.dxengineering.com/parts/dxe-iso-plus-2
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Roger, W6VZV

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Thanks, Dan.  Something I've been looking for.  Ordered 3 of them.
de Roger W6VZV