[RFI] Update... Re: external noise source identification

bill K7WXW K7WXW at qrpdx.org
Sun Dec 23 21:06:19 EST 2018

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

brevity is beautiful.

More information about the RFI mailing list