14 August 2015

CIS-60 idle

The signal, heard on August 12.08 16810.0 KHz on USB, is a variant of the CIS-60 idle, possibly for test or adjustment/calibration purposes. CIS-60 waveform is analyzed here http://signals.radioscanner.ru/base/signal231/  and here CIS-60 in this blog.
I say a "variant" since a similar test signal is also mentioned in radioscanner.ru at that same address, but in my sample, at a first glance, looking at its sonogram the 60 tones seem to be housed in what looks like a curious 40+20 (+1 pilot tone) grid: although all the tones are not modulated, the top 20 tones (41-60) appear in some way shifted with respect to the lower ones (1-40). 
After resampled the signal at 8888.88 Hz (shift * 200), from 1-40 tone to tone there is a 180º phase shift in the relative constellation, but,from tone 40 to tone 41 there is no variation (Pic. 1). As AngazU too suggests, this could point to a different phase of the top 20 tones during the initial generation of the signal. Moreover, looking at the OFDM parameters (Pic. 2), there is a different baudrate in (at least this) test mode (30Bd) with respect to the usual traffic mode (35.5Bd). BTW, a 30Bd traffic mode was also noted.
Recordings available on request.

Pic.1 - phase variation

Pic. 2 - OFDM parameters

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