Форум радиолюбителей ДВ

Весьма примечательное событие на VLF!
Стефан DK7FC и коллективка DL7NN с мега-антенной провели двухстороннюю связь в Ebnaut!
QRB = 380 km.


Hello LF and VLF group,

Today there was a two-way VLF EbNaut QSO between DK7FC and DL7NN. We
used 8K21A, 1 second/symbol, CRC16 and 20 characters.
The distance is about 380 km (JN39WI to JO60IT (my RX is located in
JN49IK)). The frequency was close to 8270 Hz, the 36 km band. Details
below.

It was inteded just to do a test to prepare for a QSO that should be
done later but the signals were so strong that we were able just to do
it.

My TX power was just about 340 W and i got 2.2 A antenne current on a
1130m ground loop antenna (60 Ohm DC resistance today).

Furthermore there was a carrier on 5170.005 Hz from my side with 2.4 A
antenna current between 10:32 and 10:51 UTC. It was immediately detected
at the other side. Maybe Albrecht can tell more later.

Finally there was a 5 character EbNaut message, 16K23A, CRC16, 2
seconds/symbol starting 12:30 UTC, which was also immediately decoded by
Albrecht!

That's a successful day which seems to show that even much lower
frequencies are possible between us.

We're planning another QSO with 100 characters per message :-) But i
need to work on the ability to generate shorter than 1 second symbols
for that...


73, Stefan


P.S.

 Finally there was a 5 character EbNaut message, 16K23A, CRC16, 2
 seconds/symbol starting 12:30 UTC, which was also immediately decoded
 by Albrecht!

That was on 2970.005 Hz !

Hello SLF friends,

Once again i want to report about another successful experiment in the
SLF range, where i'm trying to reach lower and lower frequencies.

This time a 5 character EbNaut message was decoded on a new lowest
frequency: 176.5 Hz, the 1700 km band!
As usual, the path between TX and RX is 57.6 km. It is a H field, near
field experiment.

The TX antenna is a 1130m ground loop antenna. The average transmitter
power was 460 W and the antenna current reached nearly 3 A.
Two nightly transmissions had to be stacked to obtain the SNR that is
necessary to decode the message. Each transmission takes 2 hours and 7
minutes.

Despite the lower performance of the RX loops (single turn, abt 1m
diameter, 10mm copper tube, ferrite transformer 2:240 turns, low noise
preamp) at that frequency i even got a higher SNR than in the recent
experiments at 221.5 Hz and 263.55 Hz. Does the TX antenna become
significantly more efficient on such frequencies?

The transmissions have to be done at night. The tram close to the RX
location is producing a lot of QRM and there is just a 3 hour period at
night when it does not drive arround. This is when i can be on the air
without to much interference.

The first transmission was done on January, 19th, the second on the
31th. It is noticable that the level of sferics in the SLF range becomes
stronger already, so the season for such experiments will be over soon!
Due to the presence of such QRN, it turned out that it is helpful to add
a litte E field component, although the E field does not contribute to
rise the signal level. It just helps to lower the noise level by forming
a cardioide antenna steering away from the QRN and thuse increases the
SNR.

Also it was helpful not just to aply the auto notch filter within vlfrx
tools but also to watch the outcoming filtered and blanked spectrum and
then add further discrete band stop filters to disable sidebands
appearing a few Hz arround arround strong QRM peaks, like 150 Hz and 300
Hz.

As usual, the attached screen capture shows the signal post-processing
and message decode and resulting SNR of the stacked transmissions.

The next step is somewhere between 100 Hz and 150 Hz :-)

73, Stefan

del

Как то случилось, что искал сей документ и не нашел.

Многое у нас разбросано по темам где происходило обсуждение и "к слову пришлось"... Уже иногда и Яндекс нам не в помощь. Прежде серьезно помогал.

Потому решил не беспокоить Александра R7NT, а просто создать сию тему.
Просто, чтоб было легче искать.

Линии сии порождают навигационные передатчики "Чайки" и Loran (не работает в теущее время - 2020г)
По ним иногда удобно калибровать программное обеспечение - Spectrum Lab, например.
Посему тема основана в этом разделе.

Сам список по ссылке:

http://136.su/index.php/topic,80.msg10183.html#msg10183

Александро, LU8YD просил опознать станцию...
Оказалась наша RDL.
К сожалению, не знаю точно с какого передатчика ведут передачи на 21.1 kHz


Unid signal received in South Argentina locator FF51XC in 21.2 KHz FSK DFCW  best signal time 02:30 UTC not H24 Tx
 
Attach audio filtered and screenshot in my SDR Console + Afedri receiver.
 
Can anyone help me to identify this VLF station?
 
Thanks in advance
 
Alejandro LU8YD



The Russian "RDL" on 21.1 with one of its regular transmissions. The
call sign is used at various transmitter sites on several frequencies
(including 18.1 kHz).

--
David L. Wilson

Вложения слишком большие, потому выклал на я-диск.

МП3 - запись сигнала:

https://yadi.sk/d/Vajn2cmF7ds2nQ

Картинка СДР консоли:

https://yadi.sk/i/NjL8QyiRnMhYZg

Что-то никто не обратил внимания....

Стефан тут онлайн записал атмосферики на VLF.

Hello dear friends of the low frequencies,

Thanks to Pauls web-feature displaying and capturing whistler events
from my VLF stream ( http://abelian.org/vlf/detail.php?stream=vlf41 ) i
catched a very loud and deep one, from the E field.

Listen, attached.

73, Stefan


And two spectrograms:
E-field: www.iup.uni-heidelberg.de/schaefer_vlf/VLF/whistler_E.png
RDF: http://web1.iup.uni-heidelberg.de/schaefer_vlf/VLF/whistler_RDF.png

73, Stefan

Splendid work, Stefan! Thanks for the details of what must have been the first
amateur VLF message across the globe.

It seems the VLF TX on this end is behaving itself again, thanks to
your guidance. It was good to have some company from Riccardo on Paul's
spectrograms. A bit of tinkering is still needed here before EbNaut can
be attempted again.

73
Joe VO1NA

On Tue, 12 Nov 2019, DK7FC wrote:

    Свернуть
     Hi Joe,

     Yes, the carrier transmissions were done to get an impression if and when the
     path is stable and if this is reproducable over a few days. I transmitted
     carriers for a few hours and later i tried to decode EbNaut '*' messages with
     different start times and symbol lengths.
     The results were plotted in an Excel sheet (attached) and we found that, when
     stacking 4 days, that a 3 hour long transmission starting at 17.55 UTC would
     give the best SNR of about 12.5 dB. One week later, the situation would be
     different since the path is very dynamic and the sunrise/sunset times are
     changing permanently. It looks a bit weird but in the end we managed to
     decode a 1 char, a 2 char and a 3 character EbNaut message.
     The antenna current was 1.2 A. I had some PA problems, EMC and so on. The
     antenna should have managed 3 dB more signal.
     Meanwhile the special licence for that band expired.

     73, Stefan

С праздником, геноссен!