March 2009 HF Tomorrow and - ALE III 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. 3G ALE is able to achieve faster link establishment, linking at lower signal-to-noise ratios (SNR), improved channel efficiency, same family of waveforms for both ALE and data traffic, higher throughput for short and long data messages and better support for internet protocols and applications. For 3G data operation, antenna matching systems and couplers need to provide fast tuning times, typically less than 3 seconds on new frequencies or 200ms from memory based on prior tune-up. The biggest changes are the inclusion of special purpose waveforms and the creation of a synchronous dwell structure. The new PSK waveforms, derived from the MIL-STD-188-110A serial-tone modem, are optimised for bursts rather than long transmissions, promoting system agility. Improvements in AWGN (Additive White Gaussian Noise) and fading channels of the order of 6 to 9dB have been achieved. Carrier sense multiple access (CSMA/CA) to access channels and incorporates collision avoidance. With synchronous scanning unoccupied transceivers can scan assigned channels and record activity, and sometimes channel conditions. Because all 3G ALE receivers change frequency to plan almost simultaneously, it becomes possible to know which frequency to use at a given time to establish the link. The signalling between stations within a 3G ALE network is handled by a set of predetermined control channels. Every station listens to the same control channel at the same point in time, with each control channel having a special structure that determines how stations can signal each other. Larg networks can be divided into smaller sections or Dwell Groups. Each dwell group monitors different channels. Network dwell groups can be contacted therefore as a group via frequency and/or the time they are all on air, rather than having to scan the whole network. In this way when traffic is busy, congestion is less likely. If a network is small and has only one dwell group, it is possible to contact every member with just one call. 3G ALE also incorporates a Trunked Mode, separating traffic channels from calling channels making it possible to use traffic channels heavily and leave calling channels relatively free. This maximises traffic throughput and minimises call delays. When idle, network stations estimate rather than measure the usability of traffic channels and monitor occupancy to ensure channels are not selected for new links when already in use. However, in the case of single radios like manpacks, it can take longer to establish a link as they will not be available to perform these tasks when actually receiving.
 Potential for traffic congestion and collision is reduced further by the introduction of 4 second five slot calling dwells, where the first slot is used only for tuning and listening for traffic and the last slot is used for responses and notifications. The intervening four slots are then available for calls and responses. Professional MF Wire System
- for NDB, DPS and NAVTEX /Stations
The Moonraker T Top wire system provides efficient performance for low to medium frequency NDB, DGPS and Navtex GMDSS communications. Antenna and ground systems are custom designed to specific locations to provide maximum performance. System efficiencies will vary according to frequency and ground conditions. Power capability is 1kW CW plus 100% amplitude modulation, and antenna wind survival is to 240 km/h (150 mph) without ice typically. Two 27m (88.6ft) masts/towers are required spaced 80m (260ft) apart, and an ATU (not provided). type T Top antenna/earth system, custom designed – please contact us for advice regarding design and costs - type T Top
Circular Polarised Receive System
Versatile HF "Receive System
The system is designed for fast deployment in the field. It uses Kevlar strengthened tinned copper braided wire and comes complete with camouflage satchel. and waterproof instructions. - type MRA RXMP
Please Note Type 15BC antennas will soon be powder coated, so sidemount insulators will change to suit. If you need sidemount insulators for a 15BC with heatshrink coating, please let us know you need the old sizing.
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