unid BPSK 2400Bd burst system

This signal was heard at 1245 UTC on 12168.0 KHz/USB on March 30th.
The burst waveform use a PSK-2 (prob. DBPSK) serial tone modulation of an 1800 Hz carrier at 2400 symbols per second (pics 1 and 2). Each transmission consists of 12 x 4000ms bursts, ending with a single 1500ms burst. 

pic. 1

pic. 2 - PSK-2 modulation of a 1800Hz carrier at 2400 Baud

Each 4000ms burst consists of 8 x 500ms frames (pic.3), for a total of 9600 bits; ACF = 500ms/1200 bits (of course). 

pic. 3 - frame structure

Each 1200-bit frame is structured as a preamble followed by a 67/134 bits period sub-frames, as shown in pictures 4 and 5 (the underlying sub-frames structure is also visible above in pic. 3).

pic. 4 - possible frame periods

pic. 5 - 1200 bit frame seen as a 134 bits period

Using a test-string such as "0011011000010101111" and synchronizing the stream on a 67-bit period, it's clearly visible that the burts send repetitive blocks of data. 
 

pic. 6 - 67-bit synchronized period

Unid FSK 100Bd/500, 40-bit/400ms ACF

16340.1 ---: Unid (prob. Russian) 1014 (cf) FSK-2 100Bd/500, strong ACF 400 ms (25Mar16) (AAI)

Probably an "old" RTTY transmitter sending the same pattern as a frequency marker.

SVO SiTOR-B: a curious feature

SVO Olympia Radio (formerly SVA Athinai Radio) belongs to Hellenic Telecommunication Organization, S.A. (OTE) and is a telecommunications network that serves the needs of maritime security sector as well as the needs of commercial maritime communications  across the world.

At a first glance, its SiTOR-B broadcasts comply the standard 100Bd/170Hz that is common for such transmissions (pic.1) 

pic. 1

But looking closely at the signal there is a curious feature of the Sitor transmitter which is  evident in the oscillograms of the WF module (pic.2,3)

pic. 2

pic. 3

It is not clear what causes such behavior, if it's a requested feature or a transmitter "sign", anyway is present only in the Greek SVO SiTOR-B and in all their SiTOR-B bands (8, 12, 16 and 22 MHz/USB). 

update (from my Fb page):
Reed Gaede Ha! It's clearly a harmonic resonance in the exciter, modulator, or PA. Common flaw/issue in tank-tuned tube PAs, less so in broadband solid-state units. Their engineering department is slacking.
 

Japanese Military, OFDM-30 +2 (mutichannel hybrid modem)

For several days, at a frequency of 12384.0 and 16553.0 kHz on USB (16553.0 is a constant for the Japanese MIL 8 freq signal), we heard unmodulated carriers only, and then finally they went to the data! 

At a first glance the signal looks like an OFDM 32 tones, ~70Hz spaced and BPSK modulation at 50 Baud (pic.1). A separated unmodulated tone, the lower in the spectrum, acts as a pilot-tone for Doppler correction and is transmitted at a higher level that the other tones.

 

pic.1 - OFDM analysis

studying more carefully the individual tones and especially the first two tones in the lower part of the spectrum, the signal is not properly constructed with OFDM technology but rather is a multichannel waveform with a DPSK or MSK modulation with 25 Hz shift and 50 Baud speed for what concerns the 30 upper channels.

Indeed, once isolated the higher tone, there is no evicence of carrier harmonics in the 2^ power and the phase detector shows a characteristic FSK-2 shape with 25Hz shift (pic.2).

pic.2 - absence of the carrier in the 2^ power harmonics

The 4-ary phase plane related to such channel reveals no diagonal transitions and two-state  transitions in Diff.1: signs of a DPSK or MSK modulation (pic.3)

pic. 3

The upper 30 tones are then MSK 50Bd 25Hz shift, spaced by 70 Hz.

The two lower tones just after the pilot tone (the lowest one) exhibit a BPSK modulation and a speed of 25 Baud for the first (pic. 4) and 50 Baud for the second (pic. 5). It is worth noting that:

- the sequence "0101010101" which is transmitted with these two channels is maybe used for sync purposes,

- these two tones are tranmitted at a lower level that the upper 30 tones. 

pic. 4 - the lower BPSK channel

pic. 5 - BPSK 50Bd in the second channel

Sumarizing the characteristics (pic. 6):

30 data-channels DPSK/MSK 50Bd/25Hz, 25Hz spaced (OFDM)

2 service-channels BPSK 25 and 50 Baud, transmitted at lower level than the 30 upper tones

1 pilot-tone, transmitted at higher level that the 30 upper tones

pic.6

Both 16553.5 kHz USB and 12384.5 kHz USB was previously channels for the old Japanese 8-tone mode, probably a litlle mis-tuning.

CIS 5 x MFSK-16 + BPSK 250Bd (2)

Just to point out some interesting analogies with a similar MFSK-16 signal, heard in the latest days of the past September 2015.
That signal had the same MFSK parameters, 5 x 16 tones 10Bd 20Hz, but with FSK inserts each 10 seconds rather than the BPSK inserts seen in these days . SOM and EOM shows the same style. While the BPSK version has a fixed lenght of 21:05 minutes, the FSK version had a 33 seconds lenght and was repeated each 15 minutes.
One could say that the BPSK version seen in these days is a sort of evolution of the semptember FSK (test ?) version, but it's probably a speculation.