9MR Royal Malaysian Navy, two FSK channels

"RY/SG" test tape continuously transmitted by 9MR Royal Malaysian Navy (RMN) [1], spotted thanks to the KiwiSDR owned by SWLOI33 in Jakarta, Indonesia. The interesting aspect is that the test seems transmitted simultaneously on two FSK channels, 2 KHz away: 50Bd/900 on 6483 KHz and 50Bd/1800 on 6485 KHz (Figs. 1,2), unless it's a bad defect in the FSK modulator.

Fig. 1

Fig. 2

The test message

JULL JULL 9MR 5/9/10 RMMJ MRB MRB RYRYRYRYRY 9MR 5/9/10 RMMJ MRB MRB SGSGSGSGSG AR

is transmitted in blocks of 718 bits using 5-bit ITA2 (Baudot) alphabet, decoded using a variable framing which results in alternation of stops with a length of 2 and 1 bit (say 5N1V i.e. a variable number of stop bits but at least one) as already specified in this post (Fig. 3)

Fig. 3

[1] http://i56578-swl.blogspot.com/search?q=9MR

https://yadi.sk/d/wiOZsCrHB6EZdA 

9MR - Malaysian Navy, uncommon FSK shift and ITA2 framing

(a joint analysis by me, ANgazu, Cryptomatser)

 

 

9MR 9/10/13 RMMJ MRB MRB RYRYRYRY 9MR 9/10/13 RMMJ MRB MRB SGSGSGSGSG AR JULL JULL

is the Id & "RY/SG" test tape transmitted by 9MR Royal Malaysian Navy (RMN) [1], picked up using the  VR3BG KiwiSDR located in Hong Kong and tuned on 8461.1 KHz and 6483.1 (CF).

The signals exhibit two curious features, at least in the heard test trasmissions: the first consists of the used 50Bd async FSK waveform with the non-standard and quite uncommon 900Hz shift value (Fig. 1).

Fig. 1 - 900Hz shift

The second feature is the framing which is used during the test operations: as you may see in Figs. 2 and 3, they use ITA2 code (5x28) with alternating framings 5N1/5N2, i.e., a character sent with 1 stop bit followed by a character sent with 2 stop bits (say 5N1V, a variable number of stop bits but at least one)

The variable framing causes the 15-bit period visible either in the raster of SA either in the bitstream (the latter reshaped to 30-bit in Figure 2). When a block ends, it possibly uses a special character or new line that causes te one bit shift to the left.

Fig. 2

Fig. 3

According to my friend Cryptomaster, we face a 5N1.5 framing and the synchronous equipment compensates for this disadvantage, resulting in alternation of stops with a length of 2 and 1 bit. About the unusual frequency manipulator, this is a drawback of the frequency manipulation shaper: when changing its polarity, the unfiltered classical transient process is visible (Fig. 4)

Fig.4

It could be a good reason, anyway after removing/cutting the upper and lower extra-frequencies, the signal still exhibits a 900Hz wide spectrum (Fig. 5)

Fig. 5

By the way, our TDoA direction findings (6483.1 KHz signal) point to Tanjung Gelang, site of RMN's Fleet HQ of the Naval Region I.

Fig.5

As a final note, the analysis of the 6483.1 FSK  transmission suggests that there maybe some flaw somewhere.
 

Fig.6

https://yadi.sk/d/d15nXWys6iSuIg (6483.1 KHz)
https://yadi.sk/d/2gmoADztQTwT0w (8461.1 KHz)

[1] https://en.wikipedia.org/wiki/Royal_Malaysian_Navy