ARRL

AC0XU

Joined: Sun, Oct 30th 2011, 02:35 Roles: N/A Moderates: N/A

Latest Topics

Topic Created Posts Views Last Activity
E&M Modeling Software? Jan 1st 2012, 05:36 2 810 on 1/1/12
Xcvr Repairs? Jan 1st 2012, 05:05 4 1,329 on 6/2/12
Broad Band Interference Jan 1st 2012, 03:51 14 1,641 on 14/2/12
Kenwood TR-751A Memory? Dec 17th 2011, 05:37 3 1,348 on 20/12/11
Wideband RFI Bursts - Please Help! Nov 20th 2011, 21:49 11 1,717 on 11/5/12

Latest Posts

Topic Author Posted On
Wideband RFI Bursts - Please Help! AC0XU on 16/4/12
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.
Broad Band Interference AC0XU on 5/2/12
Why would a doorbell transformer generate a regular burst at regular 1.3 second intervals 24x7? Thanks for the suggestion. If the neighbors ever let me back in their house I will check their doorbell system.
Broad Band Interference AC0XU on 4/1/12
Thanks for the suggestions. Specific challenges here are that 1) the signal appears to be reradiated from multiple points; 2) the signal most likely appears to be coming from a house whose residents won't cooperate by allowing me in their house or yard.

A couple of additional observations: 1) The RFI is on 24/7, so it has nothing to do with the sodium vapor street lights. 2) When I am out and about in the neighborhood (as opposed to in my house), the signal appears to be almost perfectly vertically polarized. I think that makes the electric fence idea very unlikely.

It also suggests that if I can deploy a horizontally polarized 20m antenna, vs. the vertical that is currently my only 20m antenna, that I might be in business. I have dreams of a high gain beam, but that will have to wait until I've got some money saved up.

I received an email from the FCC, making it clear that they expect someone complaining about an RFI problem, to correctly identify the source of the RFI before filing a complaint. So... a lot of detective work is required. I read all these stories posted to ARRL about detective work done by hams to track down their RFI sources. I am wondering how the hams managed to do it without getting shot or jailed. Those guys must be far more persuasive than I have been, or they reside in friendlier towns.

My plan at this point is to measure signal strengths and loop directions, plotting the data on a high res map. I hope to be able to confirm that the signal is coming from the suspect house or otherwise to pin it down more precisely.
Broad Band Interference AC0XU on 3/1/12
Thanks for the assistance.

The RFI signal that is causing me the most grief consists of short bursts at about 1.4 second intervals. Of the material I have read from the ARRL website, this is most similar to the electric fence described there. I don't know why anyone in my neighborhood, consisting of small city lots, would have an electric fence, but I suppose it is possible.

I think that what this boils down to is tracking down the source of the RFI. I am pretty sure it does not come from my residence, because turning off the power and turning off all the UPS's makes NO difference. Beyond that, it is strongest in a one-block range around my house, or perhaps it may be centered around the neighbor's house. It is difficult for me to tell because I haven't figured out how to construct a portable antenna for 20m that has any useful front-to-back ratio. My loop does a good job - but

1) It has a 180 degree ambiguity.

2) Placing the radio and antenna in a large metal box doesn't seem to increase the front-to-back discrimination at all.

3) The direction of the signal source as measured with the loop does not appear to be entirely consistent with there being a single source. I think that multiple metallic structures, including the wiring and plumbing in my house, signposts, etc., are re-radiating the signal, making tracking down the actual source even more difficult.

At this point, I need some unambiguous DF mechanism so I can track it down. So... how can you do unambiguous portable DF at 14 MHz?




Broad Band Interference AC0XU on 3/1/12
The noise bursts are 20-30 dB over the noise floor in my station receiver on 20m. The "noise floor" is pretty high on 20m. That means that the noise bursts are stronger than most signals of interest. It isn't so bad to make 20m useless, but it is extremely annoying, because I have to work between the frequencies of the noise bursts.

For ferrite beans I use the type 31 split beads from DX Engineering and the (type 43?) baluns from Palomar Engineers.

I have what appears to be a sufficient number of beads on all of my antenna feeds.

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