ULF,
...post-processing completed. It was a rather noisy day, which required
different blanker and antenna mixing settings. At first i used the same
settings like in the recent message at 970 Hz and reached an SNR of
just 9.52 dB. That seemed to far away from the necessary level. Tuning
the levels helped to reach > 13 dB. Then, adding a small portion of
the signal of the N-S loop rised the SNR by 2 dB. A clear and
comfortable decode.
Capture attached, showing the signal processing chain and EbNaut decode.
That's a 4 character message transfer on 829.9 Hz, the 361 km band!
:-) I never thought to come down so deeply, not even one year ago.
Next? Time to try really low frequencies! ;-) Next stop is at 470 Hz,
or 638 km wavelength. Already considering SLF at 270 Hz! All that will
be in the near field from now on, but anyway exciting for me.
73, Stefan
Am 27.10.2018 13:28, schrieb DK7FC:
Dear ULF friends,
Since 11 UTC, i'm attempting to transfer an EbNaut message into the far
field at 829.9 Hz. The antenna current is 1.83 A, blown into my 900m
spaced earth electrode antenna. TX power is 320 W.
At the given distance between my TX and RX antennas, 57.6 km, this is
the lowest frequency in the far field.
I'm trying:
f = 829.9 Hz
Start time: 27.OCT.2018 11:00 UTC
Symbol period: 10 s
Characters: 4
CRC bits: 18
Coding 16K21A
Antenna current: 1.8 A
Duration: 02:45:20 [hh:mm:ss]
If the noise background is as low as in the recent 5 character message
at 970 Hz, i will have a spare of 3 dB for a decode, so i am quite
optimistic.
If successful, it will be a new record for the lowest frequency for a
message generated/received in the far field, by amateurs.
Quite cold here! The notebook is standing on the roof of my old car
while writing this email.
Now i have to wait and enjoy the nature here :-)
73, Stefan
PS: Since a few days i'm archiving/monitoring the E field ELF...VLF
stream of Renato Romero, IK1QFK. It is unlikely but i will see if he
got the message at a significant SNR...
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