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Author Topic: RFI with home PC network  (Read 2065 times)
W1EBI
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Posts: 16




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« on: August 09, 2002, 06:52:13 PM »

Sorry, forgot to post Subject!

I need advice on eliminating an RFI problem with my home PC network. I have a Linksys Wireless Access Point/DSL Router and two PCs in rooms on the second floor. My hamshack is in the basement. When I am on the air, there was interference with the wireless link and the router would crash, causing my DSL ISP tech support to notify me (too often for their pleasure, and mine). This happened nearly 100% of the time, so yesterday I replaced the wireless link with new Linksys PowerLine devices, which use the home AC wiring as a LAN. On Day One, I transmitted for 2-1/2 hours without any problem, but today (Day Two), the router crashed. Does anyone else have a similar setup, and what would be the best way to eliminate the RF from crashing the home network? Would ferrite chokes on the AC side of the PowerLine bridge and adapter do it?

Thanks,
George W1EBI
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W6OFG
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« Reply #1 on: August 11, 2002, 01:53:13 PM »

Hi George,

Your question is the answer to what I was asking about wireless networks and RFI. I kind of thought that there might be a problem. As to your RFI problem now. A few months back, I was running an Ameritron AL572 and had all sorts of problems. It was setting off my carbon monoxide detector on 20 meters and my burglar alarm on 15 meters. I put six ferrite chokes (the wrap around kind not the clip on) on the power cord for the linear and it pretty well took care of the problem. You might want to give it a try. The ferrites are available from Radio Shack and cost about $4.00 a pair.

good luck,

Harry, W6OFG
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W1EBI
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« Reply #2 on: August 11, 2002, 02:46:11 PM »

Thanks a lot, Harry.  In fact, I already coiled up the Ethernet cables going into the Linksys router.  Yesterday I was in Radio Shack and bought three of the clamp-on ferrite chokes, but have not taken them out of the package.  I saw another type in the store, they were rectangular and had a rectangular opening, came in pairs for about $8, but I wasn’t sure how they were used.  How do you "wrap" them around a cable?

I was on the air for quite a while last evening and the router stayed up, and that was before I did the cable coiling, so I don't think the problem is major.  But my DSL ISP offers a managed service, so they call me at home whenever there is a router down flag.  The wireless configuration fell over nearly every time I transmitted.

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KB0NLY
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« Reply #3 on: August 12, 2002, 08:45:31 PM »

A topic i am all to familiar with. I have had similar problems with my internet service, it is a service similar to DSL or Cable but it comes in on a wireless modem with an antenna on the roof aimed at the access point. It was a bit more of a hassle then your problem seems to be, my system has a modem in the house that sends a UHF signal through a coax feedline to the outside antenna unit which is basically a transverter that jumps it up to 2.5 GHz. The problem at first was that the modem uses a closed system UHF signal at around 450 MHz and was taking interference from the 440 mobile i use as a base. That problem was easily solved by getting better antenna seperation outside. The router however that i have the modem hooked into was having troubles when i transmitted on just about any band, 6m, 2m, and it turned out to be the ethernet cables. Since this system is 256K service it was very noticable when it was receiving interference because it would hardly load a web page. My interference problems were solved by swapping out the ethernet cables for better ones that have 95% shielding in them and by making sure the shield was grounded on both ends of the cable. My guess would have to be that any problems you are having is in those ethernet cables acting as an antenna, Ferrite chokes would help in most cases i have dealt with, in your case by coiling up the excess cable you actually made an RF choke by doing so which im guessing is why the problem went away. Wich i had that kind of service that the ISP would call me when something is wrong, i usually call and wait on hold for a while.

73,

KBØNLY

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W6OFG
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« Reply #4 on: August 14, 2002, 07:30:40 AM »

Hi again George,

The rectangular chokes are the ones that worked for me. They are made of a plastic holder that clips together on one corner. The ferrite is actually 2 "U" shaped pieces that fit together to form the rectangle. You will want to to open the clip and coil the power cable through the ferrites and then snap it back together. These things stack so you can add them as needed. For my problem, I started with 2 and added chokes until the problem was solved with 6 stacked together. The final product had one loop of the power cord with the one side of the chokes inside the loop. It sounds like your problem isn't that great and you may get away with fewer chokes. In any case it's a lot cheaper than running new CAT5. I had forgotten that the chokes were around $8.00 but that is the right price. (What the hell, I'm old!)

Good luck,

Harry W6OFG
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W1EBI
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« Reply #5 on: August 15, 2002, 02:54:23 PM »

I picked up six of those chokes at R/S, Harry.  Wrapped the AC cord from the rig power supply through four of them in parallel, but my router still crashed.  I'll go to six, but I'm really getting frustrated.  Problem is I don't know whether it's RF being picked up by the Ethernet cables or noise getting through the AC line to the AC adapter.  Anyway, thanks a lot for the tip.  Next I'll try shielded Cat5 cables, but don't have a good way to ground the ends.  Since the Linksys router uses an AC-DC adapter there is no convenient ground connection on the unit.
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KQ6EA
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« Reply #6 on: August 15, 2002, 08:51:58 PM »

They'll be grounded at the NIC in your PC. I had trouble with 40M taking my network down until I went to shielded CAT5. I had no trouble with individual PC's plugging straight into the modem. I still have an unshielded 3' jumper from the modem to my Linksys with no problems.
Jim
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W1EBI
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« Reply #7 on: August 26, 2002, 03:32:39 PM »

For any of the helpful hams who responded, thanks for the suggestions.  I tried ferrite beads and chokes on nearly every cable in the network, as well as the AC cord on the rig DC supply--no help.  I finally decided the Linksys had to go.  It's an OK appliance for a combo wireless access point/DSL router, but the RFI was its Achilles heel.  I replaced the Linksys with a WEBRamp 700s firewall/DSL router from Centrix, transferred my ISP's static IP address, flashed the latest Sonicwall s/w, and voila!  NO MORE RFI!  
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KF6IIU
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« Reply #8 on: September 22, 2002, 04:35:16 PM »

I'm surprised your power line networking is not causing you reception problems. This equipment operates all over the spectrum between 4 and 21 Mhz. I don't have personal experience with it, but similar technologies used to relay phone an cable TV sigals have caused problems in the past. House wiring is already a bad enough radiator; I can't imagine any more RF garbage on it.

I have a Linksys BEFW11S4 (802.11b router w/4 port hub) and have no problems with 100W on 40, 15, or 10; on 20 a transmission breaks the link temporarily (like a desensing problem) but does not crash the network equipment. The wirelesss hub is connected to DSL via a speedstream 5360 modem.

I like this hub a lot - the out of the box configuration provides NAT and reasonable security, and it's cheap - I got a open-box one without CD at the local big box for $120 (you don't  need any software to set it up, just a web browser.)

I have had problems with my keyboard locking up, requiring a power cycle. I have a typical home-assembled cheap-ass Communist Chinese computer with a Shuttle KT266A motherboard and noname keyboard. I can't pin the keyboard lockups on a particular frequency or operating habit just yet, and I haven't tried any mitigation with beads, etc.

Of course the ADI Microscan CRT is a major RFI producer - so I'll probably end up powering the PC off anyway when I operate.

I think the RFI issues associated with all these cheap components is going to be one of Ham radio's biggest problems in the future. They are all just circuit boards in a plastic case with no shielding.
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W1EBI
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Posts: 16




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« Reply #9 on: September 22, 2002, 04:51:53 PM »

Thanks for the follow-up note, Wiley.  The WebRamp is a neat little box, and I got mine out-of-box for $18!  So far, not one single crash.  Meanwhile, I have a new Compaq Presario for the shack (now into latest state-of-the-hamming-art for logging and contesting...) and after moving some of the coax around, no apparent RFI in that PC, which is inches from the feedlines and rig.  But I still have a handful of ferrite beads and chokes just in case.

I liked the Linksys unit OK, but could not find the source of the killer RFI.  Traded it to my son-in-law even up for the Compaq.  I'm determined to try PSK31 one of these days, maybe we'll connect.

73, George W1EBI
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KF6IIU
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Posts: 293




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« Reply #10 on: October 31, 2002, 10:11:27 PM »

To followup with some new info, I found the Linksys BEFW11S4 puts out quite a bit of noise around 7 mhz. 2 or 3 S units, and it's across the room from the rig. Most of the noise is radiated from the LAN cables. Putting a ferrite choke near the the one LAN port I had in use cut down most of the noise. It seems pretty quiet at 14, 21 and 28.

As I understand it there are shielded cat 5 cables available - I am pretty sure mine are not shielded.
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W1EBI
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Posts: 16




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« Reply #11 on: October 31, 2002, 10:23:46 PM »

Are you saying the Linksys was causing RFI to your radio?  I don't have any instruments for measuring RF, but before I swapped out the Linksys altogether I went to several CompUSA stores in the Boston area and none had any shielded CAT5 cables.  I had beads on everything and could not locate the RFI soft spot, but it's all academic now with the WEBramp and Powerline network, which actually works FB.  Also put a new Carolina Windom antenna in service last month with shorter length of coax feedline on the basement floor, so no sign of RF and the PC was quite happy during 30 hours of operating in CQWWSSB last weekend.
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