[RFI] periodic peaks in the spectrum

[Ramakrishnan Muthukrishnan]

Dear RFI-hackers:

I have been experiencing QRM from some unknown source for the past 
several months, a picture of it is here: 
<http://rkrishnan.org/files/40m-qrm.png>

This happens in every band and is repeats at 20khz. The signal is steady 
and not wobbly like one sometimes see in SMPS created QRM. When 
listening to SSB, I turn on the notch filter function on the SDR to get 
rid of the "carrier" like signal. But that only does a bit.

I have tried turning off the mains and hunting for it inside the house. 
I live in a densely populated area. All the houses use power inverters 
as power disruption is quite common in this part of the world. I have 
tried powering the house directly bypassing the inverter to rule out 
whether it is coming from my own inverter. But so far, I haven't been 
able to find the source for it within my house. If anyone has seen such 
an RFI signature and can give me some clues about what it is, I can try 
to hunt for it in the neighbourhood. I see it all the time, 24 hours! 
When power goes off in the area, the inverter creates heavy QRM and so 
this gets buried in other noise. I am getting a mains filter etc. THis 
is coming from the antenna side though (I think), as without the 
antenna, I am unable to see this signal (I found other local SMPS 
sources that way and eliminated them).

Any help appreciated.

73
Ram VU3RDD
-- 
Ramakrishnan