Tren de bursts desconocido

[ANgazu]

Hola.


Llevo algun tiempo monitoreando esta señal formada por bursts (12433 Khz (Fc) usando el SDR de Twente.
La señal sigue una curiosa secuencia de dos mas juntos y 3 mas separados.
Curiosamente, los tiempos entre bursts son irregurlares, lo que es extraño en estos tiempos en los que todo el mundo usa GNSS para sincronizarse.
No me resultan conocidos, por lo que seguire grabando a ver si acabamos sabiendo de que van.

bursts.jpg

Tambien se reciben con Kiwi en europa, pero selen tener el tiempo capado,
Saludos.
ANgazu.

[I-56578]

Hola ANgazu,
bursts realmente interesantes, puedes enviarme un file wav solo para tratar de identificarlas?

ciao
Antonio

[ANgazu]

Hola.
La señal ha cesado esta ultima madrugada. No obsante, tengo mas de dos dias de grabaciones.
Gracias a http://websdr.ewi.utwente.nl:8901/ y a http://dl5ycx.proxy.kiwisdr.com:8073/ .
Segun mis medidas, los burst duran unos 347 ms, usando una modulacion PSK8 a una velocidad de 2400 sps. La portadora nominal parece ser de 1800 Hz.
La señal me es desconocida. Le voy a enviar alguna grabacion al amigo Antonio por si el puede identificarla.

Saludos.
ANgazu.

[ANgazu]

Hola ANgazu,
bursts realmente interesantes, puedes enviarme un file wav solo para tratar de identificarlas?

ciao
Antonio

Of course, Antonio.
This is the link to download: https://www.swisstransfer.com/d/59963b3 ... 41dd4c7dee

Please, feel free to use the files in your blog as you like.
More recordings available.
Thanks for your work.

Saludos.
ANgazu.

[Rapidbit]

Mismos parámetros que a ANgazu.
Saludos
Click en la imágen.

[I-56578]

Hola

although the bursts have the same 192-symbols length sequence (the "acquisition preamble") of Link-11 SLEW, I think they are the R&S proprietray HF waveform running in their GM-2100/900 modem; likely something related to their development of X.25 protocol. The the evident matching between the two preamble sequences must be indagated.
Will be clearer in a next blog post.

(I apologize for using English...)

Saludos
Antonio


https://disk.yandex.com/i/X7iUbEcwNN9OJQ

https://disk.yandex.com/i/NIVqxcIjj6ba7w

[ANgazu]

Hola Antonio.
Good job.

Yes, it could be R&S modem since ALE2G (today) points to Guardia di Finanza and they use that modem.
Tests or malfuntion?
Also, there are a THALES non NATO data link Y Mk2, but no waveform information to crosscheck.
Wiil keep monitoring that frequency.

Saludos.
ANgazu.

[I-56578]

Hola

It is definitely not Link-11 SLEW, but there is still some uncertainty about its belonging to the R&S GM2100 family waveforms. What's puzzling is that damn 192-symbols sequence...

[I-56578]

Hola amigos,

I think that R&S use Walsh Orthogonal Modulation in the sync preambles of the GM2100 waveforms family.
The Walsh Orthogonal Modulation is accomplished by taking each three bits (tribit) symbol and selecting a corresponding 4-fold repeated Walsh sequence, represented as octal characters (0 will be 0, and 1 will be 4); the selected four element Walsh sequence is repeated 8 times to yield a 32-element Walsh sequence used for the sync symbols. Each 32-element Walsh sequence is scrambled by modulo-8 adding the pseudorandom sequence 74305150221157435026216200505266.
The scrambling sequence is probably generated by the polynomial x^16+x^15+x^13+x^4+1 (notice that a similar method is used in the sync pattern of MIL-STD-188-110B/D, see paragraph #5.3.2.3.7.2.1).




Thus, the sequence of the link-11 SLEW acquisition preamble is 5,7,6,1,4,0 and it will always begin with 70341….

[70341110261517035422612204541226] 5
[70701154265117475466616604101262] 7
[74741550225513435062656200141666] 6
[70345554261553475422256604545662] 1
[74301514221113075026652600501622] 4
[74305150221157435026216200505266] 0

R&S documentation reports the "autobaud" facility of the GM2100 waveform: "A great advantage of the transmission method employed by GM2100 is automatic detection of the received signal data rate by means of a code received at the start of reception. This means that the receiving data modem need not be told the data rate of the transmitting modem".

Well, since the different GM2100 waveforms (up to 5), in my opinion R&S probably use different sets of 6 x 32-element Walsh sequences to code data rate, FEC, (interleaver?), and modulation used in the data blocks which in turn follow the so-coded preamble. Knowing the beginning and duration of each received sequence, to reduce computational complexity, first the randomizing sequence is "removed" from the received signal and then the resulting symbols are determined by the maximum likelihood method.

I think that's the reason of the "false positive" matches with Link-11 SLEW!

That's my final guess... what do you think about it?

Antonio

[Kilo]

Eres un genio, Maestro

Saludos, 73