First, thanks for the help and suggestions. A number of people thought
my laptop might be generating artifacts, so I ran a couple of tests.
On the assumption that the laptop was generating the RFI:
1. Separating the laptop and SDR by a long USB cable that had two 31
clamp on ferrites.
2. Running the captures using a different computer.
Distance made no discernible difference in signal strength. I changed
the distance between the laptop from sitting on the SDR to six feet
away. Change in computer also made no discernable difference. I am not
completely convinced that the SA software isn't creating artifacts but
there does appear to be some signal there that it is seeing.
I put a Siglent spectrum analyzer on the feedline. I just got this box
and I haven't used an SA for forty years, so I have a bit of a learning
curve but I know the basics. There still appear to be groups of
frequency spikes separated by 10KHz. They are a good deal easier to see
and measure on the SA. There is also pairs, separated by 69.33Khz,
which are actually much stronger. The noise spans roughly 2 to 5 Mhz,
and is strongest from 2.8 to 4.2 Mhz. Net the spikes, the noise floor
is roughly -100dBm, as I would expect in my part of the world.
Based on the data I've already collected, I am guessing this source is
outside my home. Next step is to figure out how to track it down. I can
use the SDR/laptop setup, even though I can't fully trust it.
73 Bill K7WXW
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