Very interesting ALE session consisting of HARRIS Autolink-I handshake (a proprietary waveform) followed by a data transfer using MIL 188-110 App.B 39-tone OFDM modem (M39) and link disconnect: since the used technology, 1G-ALE and 39-tone, the session is almost a sort of HF flashback. The transmission has been heard on 12567.0 KHz/USB at 1140 UTC 13 December, most likely from Moroccan Military.
The Harris Autolink-I system was one of the first adatptive and automated HF systems available and was implemented in the Harris RF-7110 controller, then it was upgraded to a RF-7210A Mil Spec Autolink-II. The basic difference between the first and second generation units is in the type of utilized addressing: call signs in the 1G controllers are limited to numerical digits while 2G controllers can employ up to 15 alphanumerical identifiers.
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| Fig. 1 |
Autolink-I employs an FSK waveform modulated at 200 Baud and shift of 200 Hz (Fig. 2). Structure is very similar to Harris RF-3560 Selcall. Preamble is a sequence of reversals and its duration is proportional to the number of channels in use so receivers have a chance to lock on the signal while scanning. Then, info is about 800 ms. and consists of some control words and 4 digits numeric call sign (Fig. 3). In case of group call to test channel conditions, answers are slotted.
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| Fig. 2 |
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| Fig. 3 |
As said, the data transfer is achieved with MIL 188-110 App.B, a 39-tone OFDM waveform introduced with the first release of 188-110 Standard and not recommended for new systems by the 3rd release (188-110C, September 2011). The modulator output consists of 39 QDPSK data tones which have a constant modulation rate of 44.44 Bd for all standard input data signaling rates from 75 to 2400 bps, plus an unmodulated tone for Doppler correction (Fig. 4).
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| Fig. 4 |
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