Hello Group:
This is not so much an RFI issue, but more of a curiosity question. I've
noticed for quite some time now that there appears to be what I would call
sweeper signals that are quite strong on ten meters. Mostly in the CW
sub-band.
These signals start mostly around 28.200 MHz and sweep down in frequency
stopping around 28.000 MHz. It is difficult to actually measure the exact
start and stop frequencies as they sweep pretty fast. I'm looking at them
with PowerSDR. The signal strengths vary, with most of them being about -80
to -90 dBm. The antenna I am using is a simple ten meter dipole about 30
feet in the air. I only see these signals during the day time when the
band is open. I've never seen them after the band closes here in Florida
after dusk. As usual I've powered off the entire house and they are still
there on the spectrum display. Has anyone else seen these signals? What
might they be? Ionsondes, Over the Horizon Radar of some type, Ocean
mapping RF source? In the past I've found that Ionsondes usually sweep up
in frequency, and
cover a much broader range of frequencies. On a similar note, I've also
seen what might best be described as wideband data bursts, lasting from 2 to
3 seconds on a range of frequencies just below ten meters. Between about
27.500 MHz and 28.000 MHz. Looking at these signals on the spectrum display
it almost seems that there is a master/slave relationship between some of
these data burst signals. As one stops sending it is observed another one
starts sending. These also only observable during the daylight hours. I
know that the 27 MHz band used to be allocated to ISM devices so maybe that
is what these signals are related to. I know, too much time on my hands
and a mystery to be solved. Can't resist the urge. Anyone interested in
positing a guess?
Regards,
Karin Anne Johnson K3UU
Palm Harbor, Florida
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