[RFI] 160M RFI - 4 khz combs-
k1ttt at arrl.net
Sat Dec 19 15:11:44 EST 2015
Just a wild guess, but I would suspect some kind of power line
communications device. Perhaps it is seeing your activity as either a
signal from one of it's own devices or as interference so it starts
transmitting in that range trying to make a connection. Dsl would be 4.3khz
spacing normally, I'm not sure if there are variants that use exactly 4khz
or not. Having them remain for some time then disappear may also make
sense, if there is no activity it goes back to sleep. Hopefully you can
hear it on your rod antenna and track it down... at least you know how to
make it appear.
David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of HankP
Sent: Saturday, December 19, 2015 19:33
To: rfi at contesting.com
Subject: [RFI] 160M RFI - 4 khz combs-
For several weeks I have been plagued with a comb of extremely stable ,
clean RF carriers spaced exactly 4 khz.
At various times the comb might be only 4 or 5 carriers - at other times it
will cover from about 1710 to 1910 khz .
Day after day these carriers will be within a few cycles of the same
frequencies . Typically for instance
1811.955 , 1815.955 , 1819.955 , 1823.955. For a few days when this started
appearing only three to 5 of these carriers would be there. Then some nights
or days there would be a comb covering 1710 -1910 or so ..
One night I returned to 160 from 40 and was happy to see no carriers at all.
I preset the Alpha tune/load kicked it on and maybe 3 to 5 seconds of
carrier for a touch up. When I stood by , the band was full from 1710 to
1910. - carriers at roughly -80 dBm plus minus 5 dB or so.. The first time
this happened I was not 100 percent sure I had just not noticed the carriers
had popped on before I fired up. (These carriers appear to stay on for a day
or so after the event ) .
This morning , I checked and the band was clear of these carriers . I keyed
the K3 at about 33 watts a couple times and two carriers popped up 1831.950
and 1827.950 . I keyed again for maybe 2 seconds and another carrier popped
up at 1823.950 then sent Vs for about 5 seconds and another carrier popped
up at 1835.950. As I kept this up each time another carrier or two would
1839.950 etc up to 1851.950 . I just looked and now after about an hour more
have appeared every 4 khz up to 1817.950 . Strangely the two at 43.95 and
47.95 have dropped about 8 dB as has 55.95 ..
WOW - was going to pop on te ALPHA but just for hell of it sent some Vs in
the middle of the comb - nothing changed - moved below the lost carrier sent
a couple V and another carrier popped up. Each time I moved down another
would pop up .Ahaa - if I key at freqs just above the comb - new carriers
start popping up but I do not have to move freq -(found same was true for
low side , carriers popped up below 1800 keying around 1810. )
OK after keying at 1500 watts it spreads for 1727.950 to 1891.950 . I might
add that my 160 loop will null these sigs NE/SW and that is NOT pointed at
my house. I have probed all around the house - turned router off . DirecV
etc etc . That same heading also drops a broadband noise 10 dB at that
I built a ferrite rod antenna that tunes 160 so will see if I can snoop
outside some .today with my R10 rx. .
What am I looking for ?
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