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Hallo Stefan,
thank you very much for your message.
On 10/1/2015 4:29 PM, DK7FC wrote:
Hi
Domenico,
Thanks for your report.
I see you on my OPDS32 grabber, as you say.
2015-09-28 21:00:47 IZ7SLZ 1159km 137502.120Hz 1mHz -46.7dBOp
93% 17.9dB
2015-09-28 20:00:47 IZ7SLZ 1159km 137502.120Hz 2mHz -41.1dBOp
90% 20.4dB
2015-09-28 19:00:45 IZ7SLZ 1159km 137502.120Hz 5mHz -44.1dBOp
93% 18.8dB
2015-09-28 18:24:51 IZ7SLZ 1159km 137502.121Hz 2mHz -45.0dBOp
75% 15.2dB
Is 137502.120 Hz the frequency of your choice?
YES. CONFIRM.
If
your TX and my RX is GPS locked (or tracked) then where does the 1
mHz offset come from?
No. My Tx is not yet fully GPS-Locked but it is steered by an
OCXO. That's why i need to check the frequency and make a small
correction as done in the above OP32 sequence . After correction
QRG remains quite steady for some hours.
Maybe a phase variation due to changing propagation?
The tests carried out so far show that the
phase stability of the LF path is sufficient for transmissions
of at least 20-30 mins. Of course, it is necessary to do many
other tests with differents conditions (message and symbol
lenght, QRB, hours, seasons,...) in order to
better understand the channel capability.
There is an interesting result achieved on Sept 14, 2015 with
some my transmission of 43 characters at 0.2 s (duration = 7 min
47 s) succesfully received by DF6NM. See:
https://www.dropbox.com/s/kimklrv25sbmwiu/ebnaut_150914_results.zip?dl=0
Which
offset is acceptable to avoid SNR losses in EbNaut (at a symbol
rate that allows a QSO (in one evening! ;-) )) ?
Here i quote a Markus' observation regarding this question:
On LF, the frequency stability of
the TX and RX local oscillators comes in as an additional
variable. It is very important that these are known and stable
to better than 1/message_duration (about a mHz for a 20 minute
sequence), which requires either GPS locked oscillators, or a
very good OCXO or Rubidium. To circumvent possible
soundcard glitches on TX, it may actually be better to use a
hardware oscillator (eg. a DDS on the final RF frequency).
73,
Stefan
PS: Unfortunately not QRV on LF at the moment. I need to find a
new loading coil body because my glass coil fully broke during
maintenance attempts. Now i need something to come out with a
stronger signal because each modification on the system has to be
an improvement, by definition. So maybe i can come closer to 1W
ERP then...
OK. We wait the restoration of your coil hoping that you want
to try coherent bpsk. Your signal will be very useful for TA
EbNaut test.
All the best
Domenico / iz7slz
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