[RFI] external noise source identification

David Robbins k1ttt at verizon.net
Fri Dec 21 18:45:12 EST 2018

Well, if you can pick it up on 2' or ladder line in your basement it has to be close.  When you power down your house be sure you kill any devices with batteries like UPS's or battery powered or backed up clocks, tablets, or even your own laptop.  I always wrap the usb cord with a couple of ferrites going to the sdr as the laptop itself can be noisy.  

If its definitely not in your house then take the laptop/sdr and walk around the outside to see if you can find it stronger in one direction or another.  A handheld shortwave receiver with loopstick antenna can give good bearings on strong signals.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373

-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of bill K7WXW
Sent: Friday, December 21, 2018 22:19
To: rfi at contesting.com
Subject: [RFI] external noise source identification

GA All

My noise reduction project continues. I have been working on noise sources in my house but need some help with what seems to be an external source.

For data capture, I am using an RSPro2 and RSP-SAS spectrum analyzer software, running on a battery powered laptop. The RSPro2 SDR is connected, via window line, to my main antenna through the high Z port.

I ran four series of data capture:

SDR with nothing on any antenna port (establishing a base line, looking for artifacts).
SDR with 2' of window line connected to the high z port SDR connected to my main antenna, house power and fiber modem power on SDR connected to my main antenna, house power and fiber modem power off

Each set includes captures at 3.25, 7.15, 10, 14.15, 18.00, 21.00, 24.50, 28.50, and 29.50 MHz, all using the same SDR and SA settings.

As expected, some of the noise is produced inside my house (modems, switching power supplies, etc). I am cleaning that stuff up by switching out supplies, adding ferrites and so on.

But there is a lot of noise between 2 and 6 MHz that is present whether my QTH is powered up or down. That's what I want to focus on in my  request for help. I've posted six screen captures that show what is happening, which can found at this dropbox link:


The first four show a 500KHz span around 3.25MHz. The first three are all with house power on, the last with power off:

003 K7WXW RFI 122018
     - window line feed, 2' (evening)
001 K7WXW RFI 122118-1
     - window line feed, 2' (morning)
001 K7WXW RFI 122118-2 (AGC was accidentally switch on for this set of
     - 130' doublet (main antenna)
002 K7WXW RFI 122118-3
      - 130' doublet (main antenna, power off)

The last two two show a wider span, with house power off:

015 K7WXW RFI 122118-3 (5MHz sweep, centered at 4.05MHz)
     - 130' doublet (main antenna, power off, fiber power on)
016 K7WXW RFI 122118-3 (5MHz sweep, centered at 4.05MHz)
     - 130' doublet (main antenna, power off, fiber power off)

Whatever the source, it is powerful enough to pick up with a 2' section of window line connected to an SDR in my basement. It doesn't change when I power down the house and fiber modem. It appears to be going 24 hours a day, though I haven't gotten up in the middle of the night to confirm that. Any ideas where to start looking?

thx and 73 Bill K7WXW

brevity is beautiful.
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