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Author Topic: RFI on 2m from cable modem, Vonage box  (Read 30855 times)
AF5MS
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« on: August 28, 2013, 09:16:58 PM »

I have a Yaesu FT-8800R being used as a base in my bedroom. It is connected to an N9TAX dual band Slim Jim hanging inside near my bedroom. The Yaesu is powered by an Alinco DV-330MVT.

2m on the Yaesu is unusable due to S4-S6 noise coming from my cable modem (Arris WBM760A), Cisco E900 router, and Vonage phone box. These are all plugged into a Belkin power strip which is plugged into the same outlet as the extension cord for the Alinco. The power strip itself was eliminated by plugging all three devices  into a 3-outlet extension cord and receiving same noise.

Unplugging the power strip or unplugging all three devices eliminates the noise. I have detailed charts, but the primary source appears to be the cable modem followed by the Vonage box.  The Cisco router and Vonage box use wall warts. The cable modem uses a straight cord.

I have limited mobility and only shortly before buying the Yaesu had the modem, router, and Vonage moved into an area that I could access. Before, if a power outage required resetting of these items, I would be without internet/phone for a couple of days.

Now, they're convenient but only 3-4 feet from my hanging antenna.

Moving them several feet further from the antenna did not reduce the RFI.

I also tried enclosing the modem and Vonage box in foil lined boxes and wrapped the modem in foil, using a wire jumper to ground the foil to the coax nut. No apparent reduction.

I ordered two FT-240-43 toroids but am not sure how / where to apply them.

I might eventually be able to plug the offending devices into a different circuit in another room, but the devices need to stay within reach.

If I were to relocate the antenna in the opposite direction, it would be hanging near a 60"x30"x24" steel safe.

No RFI on 70cm. Nor is the Baofeng HT affected on 2m unless connected to the Slim jim.

Would appreciate suggestions, especially on utilizing the toroids. Understand that some obvious steps may not be possible for me and I'd prefer not to ask for help.

Mike
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Mike
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K1CJS
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« Reply #1 on: August 29, 2013, 05:27:56 AM »

I don't know if this would be of any help to you, but I had a problem with cable interference on my 2 meter transceiver once, and the source of the problem turned out to be connecting coax between the different parts of the cable system itself.  Check or have someone else check (I did see that you've limited mobility)  ALL the coax and the connectors in your cable system, making sure that the cable used is the double shielded kind that is used by the cable TV company installers.  Make sure all the F connectors are installed properly and are tightened properly too.

The cheap coax jumpers that you can buy or that are supplied with video devices can't be used with cable TV--they're not shielded well enough.  At the same time, some of the jumpers and connectors supplied with the "do-it-yourself" installation kits that come with some cable TV modems and receivers are not as good as the company installed cable either.

I have Comcast as my supplier, and the white jumpers they supply with their kits are not as good as the cable their installers use.  I bought the tools and parts and custom made my own jumpers, and the noise problems I was having disappeared.  Turns out the worst offender was the jumper from the VCR to the TV--which came with the VCR.  Replacing that cured about 80% of the problem, and replacing the rest of the inferior cable jumpers cured almost all the rest.  The little noise I had remaining didn't bother me.

Hope you can get your problem under control, and also that seeing the steps I took helps you out.  Take care and 73!
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AF5MS
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« Reply #2 on: August 29, 2013, 12:59:53 PM »

Thanks for the input. I only have internet service through Comcast, so there is only one piece of coax running to the modem.

Then, there are the two Ethernet cables to the router and the Vonage. Nothing special on those. I used what came with the devices.

When we relocated the devices for easy access, I used a 50' length of GE 73342 RG6.

http://www.homedepot.com/p/GE-50-ft-Black-RG6-Ground-Coaxial-Cable-73342/202698953#.Uh-itRuko40

The description reads:

Connect indoor and outdoor satellites and antennas in burial or above ground applications with the GE 50 ft. Black RG-6 Ground Coaxial Cable. This cable is shielded for low signal loss and included F-connectors on each end.

Connects A/V equipment
Low-loss, double-shielded cable for high quality picture
F-connectors on both ends
For indoor and outdoor use above- or underground
50 ft. long
MFG Model # : 73342
MFG Part # : 73342

I will admit that the ground wire was not attached on either end.

One thing I wasn't sure of was whether you could use an AM radio to pinpoint RF on VHF like HF. It does seem to indicate greater RF from the modem and less from the Vonage.
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Mike
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AF5MS
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« Reply #3 on: August 30, 2013, 06:15:45 PM »

I might have seen some improvement.

I took one of the FT-240-43s and looped my coax through it eleven times. Noise level on 145.17 has dropped to about S3. Other 2m freqs show as low as S0-S1. The loops used all of my excess coax, so I'm considering buying a 6' or 12' extension and a barrel connector to use the second toroid.

I'm hearing conversations that before were hidden or garbled by the noise.
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Mike
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AA4PB
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« Reply #4 on: August 30, 2013, 07:25:51 PM »

The cable RF stuff (which does include frequencies in the 2M band) is all on the incoming coax cable. You might have some poor shield connections on that cable either inside or outside the house in the interface before it goes underground. The cable companies now are using good quality waterproof crimp "F" connectors. You might check them or have the tech come out and recheck their connections.

All the signals on the CAT5 cables are much lower frequency and are stronger on an AM band receiver then they are on 2M normally.
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AF5MS
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« Reply #5 on: August 30, 2013, 07:58:42 PM »

OK, you're saying the problem is with the cable coax? The cable is overhead from the street to the front of my house. It was from that point that I added the double shielded RG6 described above. There are no other segments of coax for the high speed internet. Comcast says as long as my internet is working, there's nothing they can do.

I stated earlier that I wasn't sure how to use the toroids. But the perceived improvement I'm seeing was from using one on the antenna feed line.
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Mike
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K1CJS
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« Reply #6 on: September 01, 2013, 07:48:57 AM »

Comcast stopped using crimp-on connectors long ago.  The connectors they use now are a pressure wedge type where a barrel is pressed into a sleeve that traps and seals the end of the coax providing both strain relief and moistureproofing.  I'm not saying the ends of the GE cable you have aren't good, but they're probably molded onto the cable, and aren't as sturdy or as good as the connectors the cable company use.

I would also question the specs on that GE cable, as from your description is says double shielded low loss, but doesn't specify the shielding percentage.  Those pre-packaged cables are seldom as good as the cable that comes off the spool and from a quality manufacturer.  I'm still betting that that is where some of your problem is coming from--that GE cable.
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AF5MS
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« Reply #7 on: September 01, 2013, 01:29:40 PM »

I'm not saying you aren't 100% correct, but changing the cable coax, indeed even getting to the bulkhead where it enters the house is problematic.

And buying a new length of more expensive coax on the chance that it might help would be a last resort.

Would there be any means of diagnosing the coax issue?

The one toroid on the antenna coax helped. On 145.17, the noise dropped from S4-S6 to S3, meaning signals have much less to overcome. On other 2m freqs, the noise is S0-S1. 2m is actually usable, now.

I have ordered a 6" extension and barrel connector to allow me to wind the second toroid and add it. It will probably take a week to arrive.

Will update when that is done and will try other steps then.
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Mike
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AA4PB
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« Reply #8 on: September 01, 2013, 01:46:18 PM »

That tells me that the feed line to the Slim-Jim antenna is causing common mode currents on the coax cable shield and that the shield is picking up RFI from the modem and bringing it to the receiver. More inductance may help. Place the toroids close to the receiver.  

Have you tried moving the antenna feed line farther away from the modem and its wiring? You might also try a 2M 1/4 wave vertical whip attached directly to the transceiver (no feed line) just to see how much noise that picks up.

The cable company is bringing signal to your modem in the VHF/UHF range with a return path in the 5MHz range. Probably all the TV signals are also present on the cable even though you aren't subscribed to them. All those signals will be present on the cable all the time even if the modem is turned off or disconnected.

If the noise is only eliminated by unplugging the devices from the electrical outlet then the coupling may be between the power wiring and the coax shield.
« Last Edit: September 01, 2013, 01:56:07 PM by AA4PB » Logged
AF5MS
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« Reply #9 on: September 01, 2013, 02:44:38 PM »

Thank you.

I operate from my bedroom. The 16' coax on the Slim Jim will reach its current location in close proximity to the problem devices. Should I route it in the opposite direction, it would be very close to my gun safe, as well as being deeper inside the structure (not sure if that would matter). I could hang it at the foot of my bed, which would place it within 3' of the Yaesu and power supply (and me) but about 10' from the devices.

I did try moving the devices several feet further from the antenna without noticeable improvement.

I am confident that the problem would disappear with a different antenna or location. I had bought a DBJ-1 which I haven't used. I also bought (2) 10' SCH 40 1" PVC to use as a portable mast. I could assemble this for use at home but there is no part of the house perimeter not covered by tree limbs. That, coupled with having to ask for help, has stalled that project. I found a deal on 100' of TM LMR-400 with PL259s and bought that (looking ahead), so I've got some distance to play with, just short on installation ideas.
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Mike
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AA4PB
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« Reply #10 on: September 01, 2013, 04:38:16 PM »

Comcast stopped using crimp-on connectors long ago.  The connectors they use now are a pressure wedge type where a barrel is pressed into a sleeve that traps and seals the end of the coax providing both strain relief and moisture proofing. 

That's correct. The connectors they used on my cable upgrade were press fit (not crimp). They installed them using a special tool that looked "sort of" like a crimping tool. When I recently added phone service to the cable they replaced all the cable and connectors from the street to the modem connection and then ran a sweep test to ensure that it was all working correctly.

They also won't permit anything but a passive 2-way splitter ahead of the modem. That is so that if power goes out, the modem (which has a backup battery) can maintain phone service.
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K1CJS
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« Reply #11 on: September 02, 2013, 04:56:37 AM »

Yes, I know.  I have their triple package with a DVR and converters slaved to the DVR, and I have one of their cheap converters (basic channels only) for an outlet that I can move around.  The input from the street comes into a special three way splitter with one leg to the modem alone, one leg to the DVR system and the remaining leg to the cheap converter.  I was cautioned not to put anything else on the modem leg since it would interfere with the modem.
« Last Edit: September 02, 2013, 05:01:48 AM by K1CJS » Logged
K1CJS
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« Reply #12 on: September 02, 2013, 05:00:56 AM »

It's kind of hard, Mike, to diagnose anything to do with that cable unless it's replaced.  Try calling Comcast and telling them you have a non-Comcast length of cable and seeing if they'll replace it for you.  You could always say that you're having problems on your cable when you use your radio.  If that GE cable is at fault, you might be able to get them to replace it for you.

Sorry I can't come up with something better for you to try.  73.
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K0JEG
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« Reply #13 on: September 02, 2013, 11:31:45 AM »

Check the wall plate. Most have terrible barrels and often the cable installers forget to pull the plate and replace the connector in the wall, which could be anything from a twist-type to a hex crimp to a compression fitting.

Also check all your F connectors and look for braid on the center conductor. Sometimes it's very hard to see but if the installer's prep tool was getting dull it happens.
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AF5MS
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« Reply #14 on: September 02, 2013, 01:58:01 PM »

K0JEG, K1CJS

I do appreciate you taking the time to respond and offer constructive suggestions.

Comcast has made it very clear that as long as my internet is working, they are unwilling to do anything. For any issue inside the house, they charge $50. Could there be an issue with the coax, certainly. From the street to the house, it may be 10-15 years old. But given the speed increases I've seen, without paying for anything extra, it doesn't seem to be too faulty. The lead in goes through the wall to the plate. While I might be able to reach the plate well enough to screw the new coax on, the plate is low enough that I would have to be on the floor to take the cover off. If I did that, I couldn't get back up. The only F connectors are on the new cable.

I'd rather not have to purchase new RG6, since it appears you are telling me that I didn't spend enough on my initial purchase. I tried to avoid the cheap junk when I bought what was advertised as double shielded. I will do it if necessary, but don't want to rush into it.

Whatever the source of the noise, the first toroid eliminated enough of it that 2m is usable. Since the winding used up my slack in the antenna coax, I've ordered a 6' extension and barrel connector to have enough length to wind the second toroid. I need to wait until I see if it produces any additional improvement. It will be several days before my order arrives.

Thanks again to all who replied,

Mike

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Mike
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