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1
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

2
Луис тут попросил меня поздравить от его имени всех наших.

Merry Christmas Roman !
 
 And hope next year be really better than this
 
 Many thanks for your messages and please extend greetings to all the Russian Ham community
 
 73 de Luis
 
 EA5DOM

Так что с наступающим, геноссен!

3
Свободное общение / Просто так
« : 26 Сентябрь 2020, 19:29:48 »
del

4
Случайно, нашел вот такую неплохую статью с массой иллюстраций.

https://www.hamradio.me/antennas/anatomy-of-a-low-frequency-aviation-radio-beacon.html

Думаю, что кому-то из наших коллег может оказаться полезным.

Предлагаю в этой теме собрать ссылки на подобные материалы как с нашего форума, помнится Андрей АГЦ постил уже про маяки, так и не только.

5
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


6
Спросил у Стефана про подробности эксперимента. Потом вставлю сюда.

UPD - Стефан нам сообщает подробности:

On the TX side:
T-antenna 40m high and 1400 pF.
2.3 A antenna current, about 1 kW+.

RX side:
Cardioide antenna (2 loops + 1x E field), mixed by software
(vlfrx-tools) in a quiet location.

QRB: 323 km

73, Stefan

7
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

8
Соберу сюда позже ссылки на эксперимент Николая UA3DJG,  Александра RN3AUS и остальную информацию разбросанную по форуму.

А пока прочитал в новой RSGB о вот таком эксперименте OK8LEO:


My wspr -2 is on mf freq 474.200 kHz I will keep it running till tomorrow morning on 200 milliwatts
OK8LEO


____________________

 Hello Leo.

No luck receiving you last night but I did see you managed 3 reports from OK0BVG and DL0AO.  Well done.

I see from the WSPR reports you are transmitting power level as 500mW but the reports are -28 / -30 from under 300km.

Is this 500 / 200mW EIRP or TX power?  ( WSPR usually shows power as EIRP to account for TX antenna efficiency)

Looking forward to hearing you / having a QSO when you get the 5W PA running.

73

David  G0MRF

___________________

OK8LEO:

Hello David
 
thanks for your email
It is 200 milliwatts Tx output into 100 meter coax cable with 3db loss
This goes into unun (1 :40 ) and connected to an  horizontal  L shape antenna 1. 5 meters high 130 meter length (in total)
This is just a try but I am happy that the VSWR = 1.38 :)
Aslo noticed that more OK stations are tuned in .
Looking forward to see the improvement with 5 watts
 
Have a nice day and stay save
Leo, OK8LEO

Впервые на ДВ-СВ вижу применение широкополосного трансформатора и питание по типу end-fed.

9
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



10
Смотрю, они там приспособились довольно длинные сообщения уже слать... - [VLF TU DECODE]
Так за пару тройку ночей можно и QSO провести!)

Hello Riccardo,

Very nice! No problem to decode again. Best result was:

found rank 0 ber 3.5227e-01 Eb/N0 2.4 M -8.090035617e-02 ph 48 60,30,30,0 [VLF TU DECODE]
carrier phase: -5.9 deg
carrier Eb/N0: 2.8 dB
carrier Es/N0: -10.94 dB
carrier S/N: 21.52 dB in 37.9 uHz, -22.70 dB in 1Hz, -56.68 dB in 2.5kHz


This morning the QRN was very very low, it invites to transmit something. I should think about it this weekend :-)

73, Stefan

PS: Don't stop transmitting if possible :-) I like the messages a lot. And as you can see, a 20 charcter message would have been easily possible in the same time!


Am 26.11.2019 20:28, schrieb Riccardo IW4DXW:

    Свернуть

    Hi VLF,

    I think I've solved the isolation trouble.
    So, before another day of bad WX, I'll try again another message:

    f = 8270.003 Hz
    Start time: 21:00:00 UTC
    Symbol period: 15 s
    Characters: 13
    CRC bits: 12
    Coding 16K21A
    Duration: 7h, 20min
    Antenna current: 660 mA

    Reports are welcome.


    All the best

    73 de Riccardo IW4DXW

11
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

12
Yaesu FT-897D c TCXO
Yaesu FT-857D c TCXO
Yaesu FT-817ND
Yaesu FT-991A
Yaesu FT-990
Kenwood TS-2000 - требуется доработка приемника.
Kenwood TS-590 - требуется доработка приемника. (работает на передачу 1 мВт)
Kenwood TS-850S
Kenwood TS-480 - требуется доработка приемника.
Icom IC-756PRO
Icom IC-746
Icom IC-7000
Icom IC-706MK2G - прием на ДВ не очень, но принимает.

Начинаем дополнять список.
Считаю тему полезной для новичков.

Детали по доработкам приемника- перепайка или установка-снятие перемычек- смотрите в тексте ветки.

13
С праздником, геноссен!

14
ДВ антенны / Антенна Луиса EA5DOM
« : 26 Сентябрь 2019, 23:58:32 »
Луис мне прислал тут письмо с описанием своей антенны.
90м вертикал.
Насколько я понял, конструкция похоже на ту, что испытавл недавно Андрей RN3AGC  - удочка с балкона и два провода параллельно вниз.
Заземление- трубы холодной воды.
Только живет он повыше, потому и эффективность антенны получлсь в разы повеселее.
Пишет, что усилитель перенес  на терасску крышы, я так понимаю чтобыне шумел вентиляторами и не мешал домашним спать и готов вещать чуть не круглосуточно. -)

Оригинал ео письма:

Привет Роман !

I have answered in the Russian group. Hope Google translator is not extremely bad on Russian
I'm using English->Russian translation, which should work better than Spanish->Russian

Hope to get the PA working in the top terrace soon. So I will be able to keep it running all night long
without fan noise at home. And then we will be able to get the good openings at sunrise in your QTH

I read that you don't understand how my antenna work. May be I can explain you, so you can translate

I live in a 26 floor building tower. The top terrace is flat (no roof with tiles) and about 80m to the ground
Then I have a 10m fiberglass pole. The pole supports a vertical wire and two sloppers to provide some capacity
about 150pF. The coils to resonate the antenna are also in the top terraza and the PA should be there. Actually
is feeded by a coax from QTH in the 16 floor

So fa so good. But the ground of the coax or PA is connected to a metal pipe which runs down the building to
the basement. This pipe is part of the fire extinguish system and is filled with presurized water and in the basement
connects with the main water distribution grid

So this is a 80m pipe which is not just ground but part of the antenna. The high voltaje runs from the coil to the 10m
fiberglass pole and sloppers. But from PA ground to the basement only RF current runs trought that pipe

The result is that the whole pipe is part of the antenna and radiates. So the effective size of the antenna is 80+10m
The performance is very very good. I have not being able to calculate the real radiation resistance, but should be high
And with 3A RF this antenna should be radiating a few watts. That's why my signal is strong

Another important thing is the radiation angle, which should be low, as the building is hight and isolated from others
and also the nearby mediterranean sea can help for a good takeoff to Reunion island, for example

73 de Luis
EA5DOM

А это результат его работы:

http://136.su/index.php/topic,18.msg24947.html#msg24947

http://136.su/index.php/topic,18.msg24937.html#msg24937

Усилитель мощностью 1300Вт


15
Технический раздел / UA4AAV set-up. PA, ANT, LOAD COIL, ect
« : 19 Сентябрь 2019, 22:57:52 »
Коллекивно решили собрать все ссылки по сетапу Виктора в одной теме.

Начиналось всё отсюда:

http://136.su/index.php/topic,74.msg24280.html#msg24280

Power Amplifier./Усилитель мощности:

http://136.su/index.php/topic,74.msg24283.html#msg24283

http://136.su/index.php/topic,74.msg24288.html#msg24288

Fan cooling system/Система охлаждения:

http://136.su/index.php/topic,74.msg24289.html#msg24289

Input  transformer 1:16/Входной трансформатор 1:16:

http://136.su/index.php/topic,74.msg24290.html#msg24290

http://136.su/index.php/topic,74.msg24339.html#msg24339

Anode current.Ток Анода:

http://136.su/index.php/topic,74.msg24293.html#msg24293

Antenna current/Ток антенны:
Maximum on ammeter 25A

http://136.su/index.php/topic,74.msg24294.html#msg24294

Output transformer/Выходной трансформатор:

http://136.su/index.php/topic,74.msg24340.html#msg24340

Circuit diagram/Схема:

http://136.su/index.php/topic,74.msg24338.html#msg24338

Antenna:

http://136.su/index.php/topic,74.msg24286.html#msg24286

Load coil/Удлиняющая катушка:

http://136.su/index.php/topic,74.msg24297.html#msg24297

Bushing/ Проходной изолятор:

http://136.su/index.php/topic,18.msg24849.html#msg24849


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