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I found a way to seamlessly stitch together data
chunks from a sequence of partially-overlapping exported FFT's, allowing me to
analyze phase evolution over arbitrary periods of time. Attached plot is
magnitude and phase over three hours of your phase-switching transmission from
Sat/Sun, Nov 21/22. Using 10 second averaging, the alternations every 50 s
and the carrier gaps are clearly visible. To obtain flat phase over
time, a -0.16 mHz offset was needed, implying that
your center frequency was actually 137776.99984 Hz ;-)
Recordings have been switched on again, and we
are hoping to receive a message from your cat tonight.
Best 73,
Markus (DF6NM)
Sent: Sunday, November 22, 2015 12:47 AM
Subject: Re: LF: Phase shifts on 137.777 kHz
Yes your signal is really good now! Not exactly
"audible" here but easily visible in Stefan's QRSS-10 slot, and sometimes
faintly discernible in my wideband colour-DF in 0.67 Hz FFT
bins.
The QRM has ended at 23:03. I'm sure it was
just an unintentional coincidence, and the OM might not have
been aware of our TA experiments.
Interestingly, our cat (his name yet undisclosed)
has also come upstairs and made his bed beside the receiver. Would you be ready
to send EbNaut sequences tonight? My receiving method is currently set up
for 32 minute FFT chunks and is thus limited to half-hour
sequences. So 4 s symbols at 8k19A may turn out too long for any meaningful
message. One or two seconds would be fine, and given your signal strength and
frequency accuracy, a fine-search for the actual starttime would be quite
feasible. Paul is recording continuously and does not have a
length limitation.
All the best,
Markus
Sent: Sunday, November 22, 2015 12:20 AM
Subject: Re: LF: Phase shifts on 137.777 kHz - QRM
now
Hello Markus and
Paul,
There is much jubilation at this QTH thanks to your spectra,
reports and
encouragement! Our cat is waiting with bated breath for you to
receive
its name on LF.
Advancing the phase by 16pi was to no avail,
but an XOR between the
divider and 4427 driver seems to have done the
trick.
I think 4 seconds will be good for symbol length until I can sync
the
arduino accurately to UT. At the moment I have to do it by
ear!
A new and better aerial was raised today so things are looking
up.
Thanks to the EbNaut Experts!
Joe
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