[RFI] Local noise environment

[Pete Smith <n4zr@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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Updated 9 Jan 04
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