[RFI] 4khz spaced birdies

Tim Duffy K3LR k3lr at k3lr.com
Tue Jul 17 20:14:26 PDT 2012

Hello Hank:

I have observed this same 4 KHz RFI interference coming from wall warts,
computer power supplies and switching power supplies used for charging
batteries, etc.
They could be your own power supplies or a neighbor's. In every case - the
RFI uses the AC mains power line as an antenna - so they can be heard for
considerable distances.

Tim K3LR

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
Behalf Of pfizenmayer
Sent: Tuesday, July 17, 2012 9:39 PM
To: rfi at contesting.com
Subject: Re: [RFI] 4khz spaced birdies

  About two days ago I started  getting families  of carriers spaced exactly

4 khz apart - usually in groups of about 15 -20 carriers - and the groups 
seem to move 10 to 20 khz from time to time then stay there for some hours. 
So far only detectable on 40 meters (two groups , one group starting at 7000

up to about 7060 and another group starting about 7132 and ending about 
7176) and on 80 meters starting about 3496 and going to 3576 at the time did

not find another group up higher on 80. The carriers are very stable and I 
do not detect any modulation on them - guess it could be very slow phase 
change which I am not looking at . If any there on 20 it is extremely weak 
and in noise - When checking  , the frequencies on 80 and 40 do not appear 
to be harmonically related.

  The carriers are not on exact 4 khz steps - always appear to be about 50 
cycles below the integer freqs.  (6999.850)

  I have checked on different receievers with entirely different 
architecture (Orion II and Drake R7 ) and they are there on both. I cannot 
find those signals anywhere in house with ICOM R10 rx and its ant held 
against power lines , computers , router , TV sets ,stoves . refrigerators 
,a/c  etc etc etc. 40 M rotary dipole at 50 feet seems to null NE/SW but not

a deep null as I normally get so may be very close . Too damn hot to walk 
street with R10 and loops right now and bum knee .

  Any ideas what this might be ?

  73 de Hank K7HP

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