SCS/ALE: a 2G ALE Modem/Controller for DR-7400 and DR-7800 P4 modems

 

SCS/ALE controller (2G MIL 188-141 ALE) supports two modes: ALE/PACTOR, see the video below, and full stand alone ALE. In ALE/PACTOR existing PACTOR software needs to know nothing about ALE. The PACTOR Connect request is turned into an ALE Linking Call, which if should fail, results in the modem telling the PACTOR software that the PACTOR Connect failed. If the ALE Link is achieved then the PACTOR Connect process proceeds. After the PACTOR is complete, the ALE Link is cleared and ALE Scanning resumes. Thus no modification of existing PACTOR software is required for an ALE front end operation. The Bluetooth option must be installed to have full ALE operational awareness when in ALE/PACTOR mode.

 

In stand alone ALE one can use PACTOR or AMD messaging or any external modem where the DR-7800 series modems provide an external modem sense PTT line to reset the ALE Link timeout. The MS110A hardware or MS-DMT software modems can be used. To use PACTOR the Bluetooth option is required.
In addition many additional HF transceiver used in MARS and SHARES have been added from reuse of source code from the MARS-ALE Radio Control Library where simple split VFO is being applied where needed for ALE Quiet Scanning and dropping out of split for TX. The use of PA relay bypass commands where applicable. No other external ALE controller on the market takes these steps.

Thanks to my friend Steve Hajducek from "MIL-STD tools for MARS Multimedia Library" group:
https://www.facebook.com/groups/MARS.MIL.STD.TOOLS.LIB

PACTOR-IV ("Dragon" modem) BPSK/QPSK

PacTOR-IV transmission using BPSK and QPSK modulation and speed of 1800 symbols/sec (in both the cases), without the characteristic PacTOR-IV spreading factor used at lower data rates. The presence of the spreading can be detected running the 'AM detector' module of SA and looking at the phase vector of the signal: in fig. 2 the AM detector exhibits a single baudrate line (so no spread factor) and the phase vector has a normal trend.

fig. 2

Instead, the AM detector in fig.3 exhibits multiple baudrate lines and the phase vector assumes the characteristic sawtooth ramp. Note that the base speed is about 112.5 Baud (the lower baudrate line and the frequency in the phase vector) while the speed detected by tha analyzer is 1800 Baud: this is a spread-16 since 112.5Bd * 16 just results 1800Bd.

fig. 3

Modulation vary according to the channel condition (PACTOR-IV is an adaptive mode) and the resulting constellations are visible in fig. 4, the related phase vectors are shown in fig. 5

fig. 4 - constellations

fig.5 - phase vectors for BPSK and QPSK blocks

A distinguishing characteristic, other than the 3300ms block length, is the 239 symbols lenght of the BPSK and QPSK frame structures:
239 symbols = 239 bit for BPSK (two modulation symbols, 1 binary digit)
239 symbols = 478 bits for QPSK (four modulation symbols, 2 binary digits)

Bitstreams after demodulations and frame structures are shown in figs 6,7. It may happen that the bistreams have the period length which  is the double of the expected one: most likely this is due to the  un-initialized state of the (generic) psk demodulator of SA.

fig. 6 - PACTOR-IV BPSK frame structure

fig. 7 - PACTOR-IV QPSK frame structure