January-February 2010 HF Tomorrow and - ALE II There was a time when a number of people thought that the days of HF radio were numbered. The advent of first the high orbiting geostationary satellites systems like Inmarsat providing marine and military telephone services and traffic monitoring services on ships at sea, the success of GSM mobile terrestrial cellular telephone networks, and the promises of the low earth orbiting Iridium satellite telephone system, all seemed to confirm it. Communications, once the preserve of the highly skilled professional, had suddenly became user friendly and available to the masses. 2G ALE uses an 8-ary FSK(frequency shift keying) modulation scheme designed for data rates up to 4800 bps. The data frame contains a constant pattern that is used to adapt the modem to the channel and a data payload that is forward error corrected (FEC). Lower data rates have higher levels of FEC. The 24 bit frame comprises a preamble of 3 bits for the frame type and 3 ASCII characters with 7 bits or 21 unformatted bits, resulting in a 49 bit Golay encoded and interleaved frame, which is transmitted three times.
The waveform is designed to pass through the AF pass band of standard SB equipment. There are eight 8mS tones located on 750, 1000, 1250, 1500, 1750, 2000, 2250 AND 2500 Hz, providing 125 symbols of 3 data bits each per second with a transmitted data rate of 375 bits per second. 2G ALE provided a more reliable and user friendly automated HF which generated a resurgence of interest in HF radio for long haul and mobile voice networks. However, as the size of networks and the amount of data traffic increased, by the mid-1990s it became apparent to industry, government and academia that more efficient protocols were required to provide more capacity. Most affected were large-scale HF or packet data networks where the data channel was also used for signalling. Significant improvements were made by the introduction of Alternate Quick Call (AQC) which reduced link establishment time by half, by removing some of the lesser used features, reducing the call sign address field from 15 to 6 characters and incorporating scan rates of 2 channels per second or 5 channels per second for backwards compatibility to non-AQC-ALE networks. AQC was incorporated into the Appendix A 2G standard as an option. As HF high reliability and high capacity HF voice and data messaging increased, especially by military users wanting to use HF internet in battlefield conditions, it became apparent that a third generation messaging protocol was required. This led to a co-operative research approach which resulted in the introduction of 3G ALE, standardised in MIL-STD-188-141B (Appendix C) of 1999 and NATO Stanag 4538. The standard can now support email serial data services and many other types of IP applications and is very tolerant to poor channel conditions as experienced by war fighters. While some 2G elements have been refined and retains, much of 3G ALE is new. Its adoption within the standard (Appendix C) is in additional to the 2G requirements in order to protect interoperability with existing systems and to provide the best of both worlds. (to be continued) NVIS On The Move
- for vehicles and high speed small vessels
 With the new Moonraker VL230 system it is now possible to have dedicated low noise NVIS close in local area communications up to 1200 km on vehicles and small high speed vessels like RHIBS. The rugged system features low power and conveniently lays down when not in use. Grounding can be provided by a vehicle’s metal roof (min 2.1m long) or by a lightweight aluminium base plate mounted on the vehicle. An EMP/Overvoltage system is provided at the antenna feedpoint. A coupler can be provided or you may use your transceiver’s ATU. Adjustable roof bars are also available. The design incorporates inherent filter qualities, automatic frequency tuning, narrow bandwidth and excellent NVIS propagation. ALE is possible, depending on ATU capability. - type VL230
DC and AC Line Lightning Protection
- for marine vessels - types DCL and ACL
 DC and AC external cables feeding navigation lights, wind speed and direction indictors, etc., can carry transient over voltages to other instruments and electronic devices such as chart plotters, computers and the like, to cause damage. The Moonraker DCL or ACL Protector, fitted at the cable entry point to the vessel, acts to prevent this happening by clamping any over voltage on 12 or 24 volt DC and 110 or 220/240 volt AC cables and conducting surges safely to ground. - type DCL - type ACL
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