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What's causing these horizontal bands of noise?

It's the middle of the day here in a low density city neighborhood. They were not present about 20 minutes ago; now they are even stronger and filling in the space between the lines.

  • Cannot hear any lawnmowers or other engine equipment, very quiet outside.
  • Shut off all the power to the house, ran off a battery, still see the same thing.

How do I figure out what these horizontal lines are?

IC-7300 spectrum with periodic wideband noise.

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  • $\begingroup$ Welcome to this site, and thanks for a great first question. Could you make an audio recording of this for us? $\endgroup$
    – Mike Waters
    Jan 4, 2020 at 21:06
  • $\begingroup$ This is a very wideband signal. Is this present outside the 20m band? If so, how low and how high in frequency can you go and still hear it? $\endgroup$
    – Mike Waters
    Jan 4, 2020 at 21:10
  • $\begingroup$ My guess is that it is over-the-horizon radar. If you have a rotatable beam, from what direction in respect to your QTH is it coming from? Russia? $\endgroup$
    – Mike Waters
    Jan 4, 2020 at 21:13
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    $\begingroup$ what is the time between these wideband bursts? $\endgroup$ Jan 5, 2020 at 14:38

1 Answer 1

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I've had similar noise multiple times - I've had three sources. One was a light dimmer in another room. Another was the charging circuit in a UPS under the radio bench. The third was a seemingly normal LED light bulb.

The first thing to do is to put the radio on battery power, and turn off the main breaker in your power panel and see if the noise goes away. If so, the source is in your house. If not, then you need to look outside. In my case, it went away, and then the hunt was on to locate it. Try turning each breaker off individually to see what room it is in. I had to result to a 50 foot piece of RG58 with a bit stripped off the end as a sniffer antenna to search around the shack to find the noisy UPS.

For outside searching, I take a portable shortwave receiver outside and hunt for the noise. I've had touch lamps and lamp dimmers in neighbors houses be the culprit. Corona discharge from power lines can sometimes be a problem - does it go away for a while after a good rain? If you can get a bearing with a directional antenna, that's helpful for knowing where to search.

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