Gary,
The crater profile you are seeing is described in this link:
https://interferencetechnology.com/spread-spectrum-clock-generation-theory-and-debate/
If you get nothing else from that link at least you get to look at Hedy
Lamarr.
Look at figure 5. It shows the crater profile you are seeing.
This tells you that the base frequency of a clock or switched signal is
being dithered slightly which causes it to get a little wider than a
typical narrowband CW signal resulting in the crater or Batman shaped RF
profile. In your case at such a low frequency it is probably just the
natural instability of something that switches like a switch mode power
supply drifting a few Hz rather than a purposely induced dithering (such as
the sine, triangle, or hershey kiss waveforms they are using) on a clock
to reduce emissions by spreading the noise out farther than the passband of
the measurement receiver.
This technology was used to reduce radiated clock emissions in electronics
and many clock generators have a spread spectrum mode for that reason. It
doesn't reduce the energy only spreads it out further resulting in a lower
measurement when using a fixed bandwidth receiver.
As for whether it is grow lights or some other source you can't tell. But
anything operating at a 36 kHz switching frequency with some instability
will give you that "crater" profile. BTW, 25-200+ kHz are very common
frequencies to operate switch mode power supplies so your 36 kHz falls in
that ballpark.
Earl
N8SS
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
StellarCAT
Sent: Monday, January 09, 2017 4:20 PM
To: tower
Subject: [TowerTalk] noise profiles...
Hello ... I know there is a group for this ... but I also know there are
guys on here SERIOUS about DXing and/or contesting that have had to work on
these issues so I?ve brought this here to see what responses I can get.
Two questions:
what would the spectrum profile be for a ?grow? farm?
and
for a plasma TV?
I have this noise that is there most every night ? and goes away at some
point in tot the night. It is broad ? about 36Khz wide as seen on NaP3
panadapter ... it looks like a crater cut in profile through the center
with a long raised yet flat area that is about 3-4 db above the noise floor
(non-interference part of the band) ... and at each end there is an upturn
in the noise that peaks as high as 12db above the noise floor with a pretty
sudden drop off back to the normal noise floor. It moves a bit from night
to night ? it can be as high as 3515 Khz or so (bottom at ~3480) or as
?low? as 3505 at the high end ... AND it appears as well at the bottom of
160 around 1810 or so!
I just checked where it was tonight and it is actually much wider tonight
going from 3470 ? 3530 ... so ?30Khz and at the center there is a peak!
Likewise tonight on 160 it is at 1856 ? 1888 with the same center peak.
Could this be a plasma TV? It is quite evident as noted peaking in one
direction as seen while using the HiZ 8 element receive array (dual 4 sqs).
I had this in TWO different directions .... and one of them went away
around Xmas time and so far hasn?t returned! I had hoped this might happen
... but the other one is still there.
Any suggestions would be appreciated.
Gary
K9RX
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