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[RFI] Local noise environment

To: rfi@contesting.com, topband@contesting.com
Subject: [RFI] Local noise environment
From: Pete Smith <n4zr@contesting.com>
Date: Mon, 16 Feb 2004 08:56:50 -0500
List-post: <mailto:rfi@contesting.com>
A bunch of responses, that I thought would be worth summarizing briefly.

Nobody thought that this sort of interference *level* (S9+10) is to be expected. Several people put the noise on waterfall displays in various software, and reported (or sent me images of) the resulting analysis. All but one detected a 120 hz component in the received noise.

I've done some more observations, including one just now using the waterfall and spectrogram displays in my DX4WIN PSK31 module, but without the sound card (i.e., live, not recorded) to eliminate any extraneous hum or other variables that the card might introduce. The 120 Hz line is VERY visible, and I can see harmonics all the way out to at least the 10th harmonic of 60 Hz (the display only goes down to 100 Hz). When I disconnect the antenna, all of this (along with the white noise across the passband) goes away, so I don't believe any of it is internal to the radio.

Another aspect that I find interesting is that this noise level does not extend very far up the spectrum. Given that the antennas differ for each band, on 80 meters the level is only S5-7, with much higher variability (spikes to S8), and the highest level to the south. On 20, the level is S1. On all three bands, however, the 120 Hz line remains clearly visible, and on 80 there is also a pronounced 240 hz line, particularly when the array is looking south. It may be only coincidence that I have a 500 kv line in that direction.

I had a very useful conversation with Mike Martin, K3RFI, who does RFI elimination for PEPCO and also does private RFI consulting and training. If I can summarize his comments properly, he believes that the noise source is line powered, though not necessarily a power line problem per se, could be as close as a hundred feet or as far away as 10 miles at 1.8 MHz, and that there could be multiple sources contributing to the picture as seen by my receiver. He suggests using an oscilloscope to spread out the display of the first 120 Hz or so of the signal, to try to discern a "signature" (Marv Loftness's technique), and then go run down the various source(s) one by one. Unfortunately, I don't have a real oscilloscope, and the Winscope software I have isn't very helpful in doing this.

Sounds like I'm going to have to engage my power company. Wish me luck, and thanks, everyone, for your inputs.

73, Pete N4ZR
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