D-STAR / streaming audio DV mode

This is a fragment of a D-STAR transmission.

Symbol rate : 4800 Bd

Modulation: GMSK

Bitstream after demod:

I found a structure frame of 72 bits + 24 bits. The first 72 bits constitutes the voice frame and the last 24 bits constitutes the "data frame" ( 96 bits for each slot ).

This is the D­STAR radio frame structure in DV mode.

HF ionospheric test ?

Transmission received this morning by many "utility listeners" on the 3600 and 7506 KHz. After a short analysis I found some useful info:

Pic. 1

Pic. 2

Pictures 1 and 2 show the whole signal.

Pic. 3

focus on unmodulated tone spacing ( ~ 1000 Hz ) and time duration ( ~ 1 sec ).

Pic. 4

Max used bandwidth: 20 KHz

Pic. 5

Tone-scale... nice image!

Pic. 6

Tone lenght : ~ 1 sec

Typical feature is the 10-tone scale that starts from the central frequency with steps of 1 Khz ( upper and lower frequencies ), up to a total of 20 Khz of busy band (± 10 KHz ). The signal reminds me some ionospheric tests ( like Arecibo... ) but this is only my opinion.... who knows....