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Wideband RFI Bursts - Please Help!

Nov 20th 2011, 21:50

AC0XU

Joined: Oct 30th 2011, 02:35
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I am getting powerful short-duration noise bursts from 80m all the way up to 20m and beyond. I don't see it on 10m or 6m, however. On 80m, the noise appears as a band about 3 KHz wide at every multiple of 60 KHz. At 20m, it covers the whole band. Noise bursts are 10-20 dB above the ambient noise level. I get it on my two HF antennas - a multibeam slant dipole and a multibeam vertical. I have tried shutting down all power to the house without effect. It is definitely not some kind of overload of my receiver front end - I have tried narrow band preselector filters and the noise is still there.

Since the noise is not continuous, but occurs in short bursts with < 1% duty cycle, I am wondering how I can DF the emitter. I am not familiar with DF equipment, but I have the general impression that continuous noise would be helpful.

Any ideas? Please help!!



Nov 22nd 2011, 04:00

WA0CBW

Joined: Apr 4th 1998, 00:00
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I would try listening for the bursts on an AM radio or a portable shortwave radio. Location of the bursts can be determined by using body shielding, or a foil lined box to reduce the signal to the radio to indicate the direction of the signal.

Bill
Dec 5th 2011, 14:54

AC0XU

Joined: Oct 30th 2011, 02:35
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Total Posts: 0
I used an Icom RX-7 and tracked it to a neighbor's livingroom. Pegs the S-meter from a block away. Disconnecting all his electronic equipment, his Comcast cable coming through the wall, with nothing attached, is acting like a fine wideband transmitting antenna. Seems to be a Comcast problem. Unforunately, Comcast won't do anything about it at my request, and all the neighbor cares about is his cable signals. Annoying.
Dec 17th 2011, 04:10

N5RMS

Joined: Apr 4th 1998, 00:00
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Sounds like a problem than needs the help of the ARRL. Do a search on ARRL.org on "reporting RFI". The guys at the ARRL may help with Comcast RFI.
Good Luck,
N5RMS
Dec 17th 2011, 05:44

AC0XU

Joined: Oct 30th 2011, 02:35
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Total Posts: 0
After a couple of weeks of persistence, I arranged for a Comcast tech to come out. He agreed that the neighbor's system was not only "red" on his computer dashboard, but that something on the property was putting interference back on the cable and getting to other homes. However, he told me that the neighbor did not allow him to enter the premises to fix the problem. He did indicate that eventually, if the neighbor does not permit access, Comcast will turn off the signals going to that house.

After several weeks of trying to get Comcast to fix the RFI problem, there has been no change. The RFI coming from the neighbor's property is as bad as ever. It pretty much wipes out 20m reception, and adds irritating noise to the lower frequencies as well. If Comcast is not able to fix the problem soon, I'll check with the ARRL.

Dec 28th 2011, 17:02

AC0XU

Joined: Oct 30th 2011, 02:35
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After another two months of waiting for Comcast to fix the problem, there has been no change. Their cables are generating powerful RFI over a wide frequency range, and it is especially devastating on 20m.

Unfortunately, the neighbor on whos property lie the offending Comcast cables is not cooperative. Comcast's response is that they cannot do anything without the permission of the property owner. Seems like a catch 22 situation.

I have searched the arrl.org website for "reporting RFI", and did not come up with a useful link. Does anyone know how to engage the ARRL for assistance in such matters?
Apr 9th 2012, 11:44

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
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Quote by AC0XU
I have searched the arrl.org website for "reporting RFI", and did not come up with a useful link. Does anyone know how to engage the ARRL for assistance in such matters?

When in doubt as to how to contact any HQ staff, you can always either call the main number, 860-594-0200 or send email to hq@arrl.org and describe what you are looking for. If you say that you are having an RFI problem, the staff that answer the phones or email will know to send you to the ARRL Lab.

Most of the RFI cases are handled by Mike Gruber, W1MG, in the ARRL Lab. I'm at home right now, so I can't look up his direct number, but you can reach him through the main number or by email at rfi@arrl.org.

In cases involving cable-television interference, the cable company is correct; they can't go into the house without permission, but they are required to terminate service if leakage above the limits can't be corrected.

Mike Gruber has a contact on the Society of Cable Telecommunications Engineers Board of Directors who is very instrumental at getting cable companies to address problems. What I suggest in this case, you provide a complete documentation of your attempts to resolve this, written in a way that Mike can forward directly to his contact and hopefully, we can see this get resolved in a much more timely fashion for you.

Ed Hare, W1RFI
ARRL Lab
Apr 16th 2012, 17:32

AC0XU

Joined: Oct 30th 2011, 02:35
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Total Posts: 0
After many phone calls and emails, Comcast did send a team out to the neighbor's house. Apparently, they re-wired the cable system in the house. That was nice of them.

Unfortunately, that is not the end of the story. While the neighborhood cable system in general appears to be less of an RFI emitter now, the neighbor's house is still transmitting powerful signals. It seems that Comcast was able to decouple their system somewhat from whatever in that house is producing the RFI, but the over-the-air RFI is pretty much unchanged. The level of the RFI is 20 to 30 dB above the general noise floor on 20m, and it persists, albeit at lower levels, in the 40m and even the 75m bands as well.

I have tried active noise cancellation. Unfortunately, those systems apparently don't do much for bursty noise.
Apr 26th 2012, 03:58

W5DRO

Joined: Mar 25th 2009, 10:43
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Problem is problem is not the house cable and being "Red" just means that the cable signal to the house CPE is not a good level just + or - what the company wants to see.

You could have a door bell transformer in the neighborhood shorting out. I have seen this before.

You need to use a Yagi antenna and DF where the noise is coming from
Apr 26th 2012, 10:53

W1VT

Joined: Apr 4th 1998, 00:00
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The difficulty with null cancellation is that you need a point source--it is likely that the house wiring spreads it out so that is not effective.

I've heard that null cancellation can be effective with an isolated powerline issue at 50MHz--the frequency is high enough that the interference only comes from the pole, not the pole and all the wiring around the pole. It helps that some 6M operators don't need to address the HF RFI.

Zack Lau W1VT
ARRL Senior Lab Engineer
May 11th 2012, 01:06

N9AAT

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
Be cautious with this one. I work for the FAA and we recently had a similar problem; owner would NOT grant access, and we finally had to have the sheriff come out. Our techs cut off one circuit at a time until they found a chandelier base with an added piece of Romex which went through a wall, and then nowhere. Our people left and the sheriff followed up. We never heard, but it may have been a secret room with a lab inside. Just a word to the wise.

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