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Re: VLF: EbNaut for QSOs, beaconing and grabbers (?)

To: "[email protected]" <[email protected]>
Subject: Re: VLF: EbNaut for QSOs, beaconing and grabbers (?)
From: IZ7SLZ <[email protected]>
Date: Wed, 18 May 2016 14:45:02 +0200
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Hello EbNaut-ers, group

Many compliments to all OM involved in latest VLF successfull activities with EbNaut.
In particular to Stefan for surmounting all obstacles for working so well even the 6,47 kHz and to Paul for his excellent receiver setup.
Again thanks to Paul, Wolf and Markus for their invaluable softwares and works.

We are following with much interest your tests and the technical solutions adopted. Unfortunatly many of us are still not ready to receive your signals or to radiate on VLF.

In the beginning of this year,  we have  demostrated that EbNaut works very good also on LF. Some QRO and QRP trasmissions from me, Markus, Paul, Andy, VO1NA were decoded.  Some EbNaut tests are still in progress with success between me and Riccardo IW4DXW.

Put on air,  or receive an EbNaut signal on LF is certainly more easy than on VLF,  despite both  TX and  RX introduce further frequency errors and stability problems that need to be managed.
So this is an invitation to the LF operators to try this mode.
If i have well understood Michel,  F5WH is working on that, that's good news !

I'm now running an LF receiver and i'm saving some "EbNaut-ready" audio wave files . I'm using Spectrum Lab recorder function and i want to share the folder:

https://www.dropbox.com/sh/9c3nnw40nyb5pqc/AABZ6oPxpAY4IwuWFmebMSfba?dl=0

Each files starts at  :00, :15, :30, :45, allowing the recording of any transmissions within these 15 minutes and - of course - within the sensitivity of the receiver.
So, if one wants to try to transmit on LF, then,  using 8K19A as coding scheme, he must use an EbNaut messages with max 13 characters at 1 s/symbol or max 31 char. at 0.5 s/symbol.
Dial frequency of receiver is 136.000 kHz and FFT center frequency is 1500 Hz.
The same SL session is used here  for running OPDS. In this folder https://www.dropbox.com/sh/37pnfw94n1l3yxo/AAC6PsMMiDVu00JfL6b3RZXLa?dl=0
there are some files with spectrogram and detection results.
The "right-side" window of the spectrogram is centered on 137485 Hz that is the test frequency used by IW4DXW. The spectrogram can be useful to monitoring propagation/noise conditions at my location.

I will try to keep receiver always on-line. Receiver is a vintage but sensitive JRC NRD-92M (GPS referenced), and i'm using an 8 meter passive whip. Locator is JN80NU (urban noise is unfortunatly present but on night time this is very low).

If some operator wants to try my setup, advicing the transmission using the reflector,  is welcome.

73, Domenico iz7slz

  

On 5/4/2016 12:04 PM, Domenico IZ7SLZ wrote:
Hello Stefan, and "EbNauters"

I like 👍 your idea of this "beacon mode" that can be helpful to rise the activity in EbNaut.
 
By the way, the critical point of this idea is that the system will be mono-channel. Both sides (Rx grabber and Tx station) must have the frequency very, very  close to the nominal in order to get decodes by an unattended EbNaut-Rx session. As you known, "playing" with offsets can make big differences with EbNaut.
Also multi access to the channel will be a problem,  but for sure not at the beginning, with few operators.

My suggestion, for an initial activity,  is to have a grabber, like OPDS,  with a SL front-end that automatically exports  the recording wave-files. The idea is to share these recording wave files with the community using  DropBox or other means.  So every operator, after its transmission,  can attempt to decode itself by running EbNaut locally: he knowns already the parameters used and he can try to fix the offsets, without waiting for the grabber's operator job.  Note that this arrangement supersedes the mono-channel and multi-access problems.

If a transmission is also announced, then also other operators can download the files from these "grabbers" and make training on decoding procedures. Local running of EbNaut-rx.exe with files already created, does not requires frequency or timing accurancy at all. This really can increase interest on that mode.

I think that this grabber  is not so complicated to do. It will be possible to use SL recording function steered by the SL scheduler.
Maybe should be better to have some modifications in Spectrum Lab in order to  include, in the header of the recordered wave file, also the callsign of the Rx station. Modifications in EbNaut-Rx will be necessary to show the callsign in the decoding page or log.

Thanks again Stefan for your activities on VLF.

73 all, Domenico iz7slz




On 29 April 2016 at 23:43, DK7FC <[email protected]> wrote:
Hi VLF,

Now, i'm not sure what the marority is thinking about VLF these days. Many OMs are in the background. I hope it is rather interesting then annoying, that VLF stuff :-)

When comparing EbNaut with other modes, we can see that it seems to be the most effective mode, at least on LF and VLF.
On the other hand, it is complex to handle, maybe to complex for some. FFT data must be exported by SpecLab, start times must be known exactly, as well as the frequency and 'even' the message length and the symbol length. The frequency stability must be extremely good.
But from a different point of view this makes the mode as flexible and effective as it can be. So it is no critisation at all, i just have ideas how to extend the usage so it becomes practicable for more stations, maybe also on LF/MF.

Now, for a comparison to other digital modes which allow to have a QSO (e.g. JT9) or running a beacon and a 'grabber' window (WSPR or OP32) there are pre-defined settings, like the start time (each even minute for WSPR) or the frequency range or the content.

What i would like to have (and maybe others too) is a special EbNaut+SpecLab+Script(s) system that runs periodically and writes and displayes the decode result in a txt file that can be displayed on a grabber site, just like the OPDS32.txt on my LF DX grabber.
That system should be easy to install for most of the operators here. It should run automatically in the background and should consume less then 20% CPU power during decoding. A decode time of 10 minutes is no problem when it runs in the background anyway.

We could discuss and define different modes for VLF:
One mode could be 'beacon'. Definition (for example): starting each hour on 1 or 2 channels (selectable, 1 or 2 or 1+2) (= defined frequency); 30s symbols (or 10s or 60s, selectable, must be stated on the grabber page); 6 characters (for a longer callsign like IZ7SLZ)
With such a pre-definition, there's no need for an announcement, which is the main difference between EbNaut and other modes. The result, which can be even checked for plausibility (filtering nonsense-callsigns) could be displayed like the OPDS32.txt results, showing date, time, message, SNR and further relevant data. A script (written by Markus) could automatically start the decoder, read the FFT data, search for results, display them in EBN.txt and delete the FFT data file then. The FFT input size could be limited to a small value so the decode time becomes short and the file size becomes small. With 30s and 6ch this takes 280 minutes, so a beacon transmitter station could run 5 hour sequences. It's then a bit like a grabber indicating the transmitting station which QRSS mode must be choosen.

Another one could be 'QSO', with 30 or 60s symbols and 15 characters, using a single channel, i.e. a discrete frequency. A bit like JT9 but with stricter limitations.

What do you think, Markus and Paul. Could it be helpful to rise the activity in EbNaut, maybe also on LF? Would someone of you provide the scripts or maybe a special decoder edition for that task?

73, Stefan


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