Stefan,
Congratulations on another excellent milestone; opening up fascinating new spectral territory with EbNaut links at 970 Hz and 829.9 Hz.
Your comments regarding 470 Hz and even perhaps 270 Hz add to the excitement. Propagation should be fairly stable there, compared to frequencies near 2 kHz, but your experiments may the best indicators.
I wonder if a different type of lightning cancellation would be helpful at these lower frequencies. Below 2 kHz lightning noise dominates and grows with decreasing frequency until ~ 1 Hz where micropulsations dominate. For frequencies near and below 1 Hz some micropulsation cancellation can be easily achieved. For frequencies 5 kHz and higher a fair amount of lightning cancellation can be readily achieved in many scenarios. But I wonder if a different type of lightning noise cancellation might be helpful at frequencies near and below 1 kHz, and particularly at and near SLF frequencies where (a) natural noise is dominated by lightning, (b) time between strokes is closer to the period of the desired signal (rendering blanking less effective), and (c) long sferic tails yield a different character to the temporal signature being canceled.
Looking forward to your continuing explorations!
73,
Jim AA5BW
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...
