7 July 2015

Israeli Navy hybrid modem in DSB/ISB ?

This is the first time that I see the Israeli Hybrid OFDM/Serial modem running on both the two sidebands: I did not analyze the contents of the two signals so it could be a DSB or ISB modulation but in any case the presence of the "supposed" carrier (10164.0 Khz) is quite odd since DSB and ISB does not provide its transmission. So, what I may say about that carrier? does it belongs to the signal?
Although 10164.0 has been reported as belonging to 4XZ Israeli Navy some years ago (precisely in 2013) and the waveform definitely refers to Israeli Navy, this frequency is very often used by the Russian Navy in T600 mode: many logs report such transmissions just on this frequency.
The second interesting point is the offset of the two signals from this "supposed" carrier. The first preamble tone is located at carrier+1000 Hz in the upper band (d1) while it is at carrier-800 Hz in the lower band (d2): ie the two lateral bands are not symmetric with respect to the carrier and that's wrong in AM modulation, other than in dual and independent sidebands.
The strenght of the two signal is just the same, then it is not the case of "fake" signals.
Concluding, it may be that this is something like a test  or something wrong/failure in the transmitter. I will try to pay a look at that frequency, if possible at same time of reception (2135z).

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