[RFI] Inbound RFI - strange source affecting 160 and 80

Stu Phillips stu at ridgelift.com
Sun Feb 21 15:15:08 PST 2010

Sorry hit the wrong button!


I'm wondering if anyone has seen an RFI source like this before?

- At isolated (and generally short) periods, the RFI is gone. 
- It has two modes... 
- Mode A - a repeating pattern every 18 KHz with a  
  central noise "splodge" about 3-4 KHz wide with two "sidebands"
equally spaced +/- 5 KHz from the 
  center of the RFI. 
- Mode B - a 500 Hz "spoldge" of noise repeated every 18 KHz 
- Both modes appear to have multiple "sub-carriers" within the noise -
it's hard to tell but it 
  appears that these carriers carry some form of modulation. 
- Both modes exhibit excellent frequency stability 
- Both modes deliver about -76 dBm into my receiver - that's around 35
micro-volts - pretty hot! 
- Some patterns have emerged... typically early in the morning before
7am, mode B is present. It has 
  transitioned to mode A several times at 7am and continued in this mode
until about 9am. Then it 
  reverts to mode B. At the weekend, its often in mode A all day long...

I've spent a lot of time over the last 3 weeks since this appeared
trying to track down the source...

I've documented the sordid details on my blog at
http://1vc.typepad.com/ethergeist if you want the gory details but
here's a summary.  There's a spectrum shot of mode A on the first post
in the RFI Hunters series - I primarily use my blog as a documentation
archive for my own use and hopefully to help others waste less time than
I do!

- Killed the house power - its not in the house
- Checked the house for battery powered devices with the power killed -
still external
- DF'd the likely "source" three different ways with the same result
- Looks to be coming from one particular house and likely coupled in the
AC power lines

I'm trying to get the occupants of the house to let me go around the
outside of the property with a DF antenna to see if the RFI is coming
from the house.... or point to having to look somewhere else.

I know that speculation about the source is problematic but in this
case, I may need to get one of the utility companies involved to get to
the next step - knowing who is most likely would be very helpful.

Stu K6TU

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