Hi Edgar, VLF,
Here is a summary of the attempt to decode a 2 character EbNaut message
on 17.4701 kHz
The message has been transmitted each evening from the 7th to the 13th
of April. After decoding a 1 character message after just 2 days, it
was highly likely to be successful trying to decode 2 characters after
4...5 days in the stack.
Unfortunately there seemed to be a timing problem in SpecLab, despite
the use of 1PPS+NMEA. There was an unexpected time offset in the files
which lead to a poor SNR for certain days. After a few days we decided
to restart SpecLab. The 13th was the first day after the restart. It is
shown that the best SNR appears after the expected time offset again.
Here is a table showing the noise amplitude during the transmission
time, the calculated weighting gain, the determined carrier S/N of the
day at the expected settings, the carrier S/N after time offset
correction.
| day |
noise during TX time |
+- dB |
Carrier S/N |
Remarks |
| 07 |
5.35 |
0 |
5.75 dB |
2 char | @
0 Samples |
| 08 |
7.30 |
-5.40 |
-10.62 dB |
5.87 dB @+6
Samples |
| 09 |
5.65 |
-0.95 |
-10.08 dB |
5.68 dB @+6
Samples |
| 10 |
5.18 |
0.56 |
-2.08 dB |
5.90 dB @
+4 Samples |
| 11 |
6.60 |
-3.65 |
-1.53 dB |
3.63 dB @+2
Samples |
| 12 |
6.71 |
-3.93 |
-10.80 dB |
Insignificant |
| 13 |
7.57 |
-6.03 |
5.39 |
|
When stacking the 07+08+09+10+13, i'm getting a good decode of the
2 character message over the 16805 km path! See the attachment. But
unfortunately the sample offset for the 8th to 10th is information only
known by someone who already knows the message and so this is not a
valid decode for the record lists! :-(( Anyway, we see that the message
came through and this is a another remarkable result. 17.47 kHz, the 17
km band. Edgar is in reach for detecting messages transmitted on VLF
from Germany. But most likely only on that band! The propagation curves
show that 8.27 kHz would be about 50 dB harder! Impossible, even with a
kite and QRO... But, anyway we will do it some day :-)
73, Stefan
Am 14.04.2018 13:49, schrieb Edgar:
Hi Stefan,
If you get a decode from the last transmission it will be an amazing
result.
Look at the bad weather.
Regards, Edgar
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2_characters_DL_VK7_17470.png
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