LF: The return of EbNaut for Dummies

[VIGILANT Luis Fernández <luis@vigilant.es>]

Hi Stefan, EbNaut

 

A new chapter of Ebnaut for dummies follows J

 

I made a lot of tests during the weekend. Installed the TX in the same computer were the Rx is running

The small signal into a few cm wire used as Tx antenna can be received with about the same S/N as transmitted from my QTH with the

big antenna at 7Km, and this is lighting safe

 

So, using the same PC, there should be no timing issues. Also tried 4K19A and 10 seconds symbol lenghts. But ….. no decode L

I ended up with many different Tx and Rx configurations tested with no luck.

 

One of the most puzzling issues for me is decimation and FFT length in SLabs to produce files with the required length to contain the transmission

and frequent enought not to make the test a veeeery long experience. The fact of getting windows timestamped files which really start at a

different time and no aparent indication of when they end ….. doesn´t help at all

 

May be Markus and you can explain again which is the relation between time lenght of the FFT files and how often they are recorded

depending on FFT length and decimation values. Also helpful to recommend optimum FFT and decimation values for certain transmissions

which would be ideal for a LF QSO. But seems that the shorter the symbol, the more critical all becomes and would be difficult to package

a transmission and decode in less that, say, half an hour. Is there any way of “fast” EbNaut when signals are strong ?

 

I really don’t know what to test next. May be to run ebnaut_tx in test mode, which just changes the phase every symbol length

And then, analyze the recorded file with a different tool to determine if this phase changes are there ? Can this be easily done ?

 

73 de Luis

EA5DOM

 

PS: Congratulations for your amazing test with the guard rails. And yes, this is much much harder than EME ! J

 

De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de DK7FC
Enviado el: viernes, 07 de septiembre de 2018 22:10
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: EbNaut transmission test in LF

 

Hello Luis,

Another hint: Try to use 4K19A and a shorter message, like EA5 or so. Use long symbols, like 10 seconds or longer. Then, timing is less critical and you may get a decode and can tune to the best Eb/N0 and find out what the timing offset it. It would guess it is a timing problem.

73 Stefan

Am 07.09.2018 13:36, schrieb VIGILANT Luis Fernández:

Hi Domenico

 

Sorry, I’m not transmitting this weekend. Very stormy weather here, so the wires are down

I will notice in the reflector any transmission in advance. But first want to confirm that all is working ok

So that was the goal of yesterday test

 

Yes, the XOR is AFTER the 1/10 divider, and working at the final frequency 137485 Hz

 

Your auto-decoder is a great tool. EbNaut is quite tricky for average use and needs a lot of details to care about

Of course the reward is great when you get decodes with miserable signal levels. There is never free lunch ! ;-)

 

73 de Luis

EA5DOM

 

De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de Domenico IZ7SLZ
Enviado el: viernes, 07 de septiembre de 2018 13:18
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: EbNaut transmission test in LF

 

Hello Luis,

 

thanks for sharing your experiment. My auto-decoder  https://www.qsl.net/iz7slz/  is already retuned for your transmissions.

 

BTW QRM is large here in the morning time (urban location). I will try to catch your signal later in the night.

 

At least the decoder is detecting the carrier but may be there is no proper phase modulation or probably other failures

What I’m doing wrong ? Can anybody decode the message from the file ?

 

 I also suspect some issues on modulator circuit. Of course the XOR gate is following the /10 divider, is it?

 

Good luck.

 

73 all,

Domenico/IZ7SLZ

 

 

 

On Fri, 7 Sep 2018 at 11:38, VIGILANT Luis Fernández <luis@vigilant.es> wrote:

Hi LF EbNauters

 

I have been building a disciplined Rx for LF, based in a GPS LO at 120KHz and a NE602 downconverter to 17KHz

Then feeding the signal to the soundcard, also disciplined with 1pps from the same GPS

 

At Tx side a GPS LO at 1374850 Hz divided by 10 provides 0.1Hz steps at LF. Then an XOR gate is used for

EbNaut modulation from the DTR of  a COM port under Windows. The PA is just a mosfet driver (mic4452 AT 12v)

Just about 100mW to antenna but good enough to get a 20dB S/N in my Rx 7Km away

 

Stability looks pretty good and also phase modulation as seen in SL spectrogram. Also monitoring phase changes

with the SL plot display window. So, yesterday I tried an EbNaut transmission with the following setup

 

Coding: 8K19A

CRC 16

Symbol period: 1s

Characters: 6          Transmission time: 9.3 minutes

Transmitting at minute 00 and 30 every hour

 

I got the FFT files from SL and converted them to WAV files. The configuration file (SR) included the corrected sample rate

of the soundcard as well as decimation , FFT length and center frequency

 

Attached is a WAV file starting at 16:22 which should contain the transmission started at 16:30 untill about 16:40

 

The rawsym graphic shows a clear peak centered in frequency, but I haven’t been able to get a decode other than “******”

At least the decoder is detecting the carrier but may be there is no proper phase modulation or probably other failures

What I’m doing wrong ? Can anybody decode the message from the file ?

BTW, I have used a list length of 47274 and also 141823, but nill L

 

73 de Luis

EA5DOM