12 May 2016

SkyOFDM 22-tone, 64Bd QPSK, 2KHz bandwidth

this modem can be frequently spotted after the 2G-ALE handshake between Finnish MFA stations, being used to transfer data. Probably its development is by Sky Sweeper team, hence its name SkyOFDM. 
From Sky Sweeper manual
"SkyOFDM is a state of art high speed modem based on the OFDM and turbo coding technologies. It offers several baud rates (300-9600 bps) and two different interleaving options (short and long). Also there are two bandwidth options: 2.0 and 2.6 kHz.The receiver should be set to the USB reception mode.
The VHF/FM variant is not included in the SkySweeper Professional product.
This version use 22 tones with QPSK modulation at 64 Baud (pic. 2) and exhibits the same special char sent each 5 signal element periods, also visible after the ACF function (pic. 3)

pic. 2
pic. 3
This special symbol is also visible by highlighting a single tone and inspecting the bistream after the demodulation (pics. 4,5)

pic. 4 - analysis of the bottom tone
pic. 5
More info in the radioscanner site: 


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