Автор Тема: DK7FC de RC4HAA  (Прочитано 862 раз)

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Оффлайн andrey rd4hu

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DK7FC de RC4HAA
« : 21 Ноябрь 2017, 22:06:33 »
VLF,

Finally there was a decode from my 3 character message that i transmitted during the last 6 nights!
It was a bit strange, the 1 char message and the 2 char message was decoded after one night each. So 3 characters should decode in 2 or maybe 3 nights, but not longer. But there was no decode even after 4 or 5 days. Something must have been wrong.

Background: Spectrum Lab corrects the drifting sample rate using a reference signal, like the PPS pulse from the GPS module. The sample rate is measured and corrected each second when PPS is used. Usually the deviation between 2 measurements is smaller than +-1 ppm. But at RC4HAA it was +-30 ppm. The PPS pulse is usually a rectangular pulse with a width of 200 ms or less. At RC4HAA the pulse is differenciated, probably by the soundcard, i.e. it is a positive and a negative short pulse of a few us length. I concluded that this not proper looking pulse caused the high sample rate jitter. SpecLab calculates the average sample rate out of the last 60 measurements. I took this average value and put it into the 'calib table'. One can define a maximum deviation. It is assumed that the sample rate will not drift more than average +- max. deviation. Each value outside that max. deviation must be a false reference signal that will be ignored then. i.e. the sample rate will not be corrected by this value. I choose a small max. deviation of +-2.5 ppm only and expected that this will lower the jitter!
But my assumption was wrong. In fact the PPS seems to work quite well, despite the suboptimal shape of the pulse. The high sample rate jitter seems to come from the PC itselfe so the sample rate correction was working quite well, showing and correcting the high jitter each second. So i made things worse by reducing the max. deviation!
After 3 nights of transmission i came to that idea and started a second SpecLab instance to export txt files for EbNaut detections. The settings were equal, just the max. deviation was set to +- 20 ppm now!
During these 6 days i worked out how to use the -f16 option in vlfrx tools by Paul. When running the decoder with this fuction, it will tell you how deep the message is buried in each of the files (each night one).
On saturday morning i quickly saw that with the 20 ppm deviation produced an Eb/N0 of -4.1 dB from a single (noisy) night. This confirmed the assumption that 20 ppm will do a much better job than 2.5 ppm. It also became obvious that a 3 character message can be decoded after 2 nights, if the noise isn't to high. This was expected from the results of the 1 and 2 character message. The change to the small max. deviation was done after the 1 and 2 character message.

Yesterday morning i lost the access to the RC4HAA PC. It took until the late night until i got the information about the new temporary password for Teamviewer. During that time, the 6th (3rd with the 20 ppm setting) transmission was already running. But i already got a decode with just 2 transmissions. The second file (18th Nov) showed 3.95 dB less noise, so the improvement was more than 3 dB.
Now this morning i had 3 files to stack and, as expected, the decode is even better.

A screenshot of the decoder and the decoder log file is in attachment. The message is the new longest one on 8270 Hz over the 2877 km land path. 3 characters in 38 hours and 24 minutes.

My next and last goal for this year on that path is a 5 character message. It will start this early evening. A separate announcement will follow.

73, Stefan
« Последнее редактирование: 21 Ноябрь 2017, 23:22:25 от andrey rd4hu »

Оффлайн rn3aus

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Re: DK7FC de RC4HAA
« Ответ #1 : 22 Ноябрь 2017, 06:32:13 »
Поздравляю, вот это достижение!
Какие необыкновенные вещи возможны на СДВ!

Оффлайн rw3adb

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Re: DK7FC de RC4HAA
« Ответ #2 : 22 Ноябрь 2017, 20:16:10 »
Поздравляю, вот это достижение!

Присоединяюсь к поздравлениям!

Какие необыкновенные вещи возможны на СДВ!

Скорее это возможности ебнаута... но танцы с бубном ради его декодироания, это конечно нечто!
Стефан писал, что всего 300 мА ток в антенне...
Ну и безусловно 38 hours and 24 minutes впечатляют!
--_ _ _  _ _ _ --  --_   _   _-_  _--  _ _ _-- _- -_ _ -_ _ _

Оффлайн rn3aus

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Re: DK7FC de RC4HAA
« Ответ #3 : 24 Ноябрь 2017, 17:19:27 »
И вот новый рекорд: 5 символов, весь позывной!

Цитировать
Today, after 4 nightly transmissions, my 5 character EbNaut message was decoded on the RC4HAA RX site. That's the new longest message over the 2877 km distant land path.

The four files generated by SpecLab were weighted and stacked. When using the recommended list length, a few false messages appear along with the correct one. However the correct one is clearly shown as the strongest one. See attachments.
If someone wants to reprocess the result, here are the files: www.iup.uni-heidelberg.de/schaefer_vlf/VLF/RC4HAA_8270_5ch.zip

Now i will leave 8270 Hz for some time and leave the place for VO1NA. Ready for EbNaut reception here.

73, Stefan


Am 20.11.2017 14:32, schrieb DK7FC:
Hi VLF friends,

Here is a last attempt for an EbNaut DX detection on the 36 km band. I will leave the band for some weeks then, leaving the place for VO1NA..
Within 4...5 days the following 5 character message should decode over the long land path:

f = 8270.1000 Hz
Start time: 20.Nov.2017  15:30:00 UTC (daily, 4...5 days expected)
Symbol period: 45 s
Characters: 5
CRC bits: 16
Coding 16K21A
Duration: 13:12 [hh:mm]
Antenna current: 650 mA

73, Stefan


BTW: Thanks to the crew of RC4HAA to provide the receiver and computer and to produce VLF spectrograms and SpecLab txt files for EbNaut detections on the 36 km band!

Поздравляем!!

Оффлайн ra4hgn

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Re: DK7FC de RC4HAA
« Ответ #4 : 24 Ноябрь 2017, 18:59:51 »
Now i will leave 8270 Hz for some time and leave the place for VO1NA. Ready for EbNaut reception here.
Что то не пойму, про что речь идет? Он будет на VO1NA передавать?

Оффлайн Sergej

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Re: DK7FC de RC4HAA
« Ответ #5 : 24 Ноябрь 2017, 19:41:40 »
Пишет, что пока прекращает передачи чтобы освободить частоту для VO1NA и будет готов его слушать сам.