Antenna solution for Malaysian defence department
The Malaysian Civil Defence Department (MCDD) is responsible for public safety and disaster management in Malaysia. Prior to 2009, MCDD had used conventional VHF on a point-to-point and stand-alone repeater system.
For short-range communications in mountainous terrain, the traditional mobile whip antenna was less effective due to its low radiation angles. The nature of MCDD’s operations required them to be constantly on the move, which results in the radiation angle changing and difficulties in receiving.
In 2009, the Malaysian Government launched the Government Integrated Radio Network (GIRN) based on a TETRA system, which was introduced across 13 government agencies, including MCDD. It was identified that although GIRN meets the communication needs for most populated areas, an HF radio system would complement the GIRN in the rugged interior and provide consistent and reliable communications across the entire country.
The Barrett 2018 Mobile magnetic loop HF antenna was identified as being more suitable for the purpose. The magnetic loop, when correctly tuned, is capable of achieving a 10-14 dB gain in efficiency over a mobile whip. It is an autotuning antenna consisting of a hinged arm (the loop) mounted to an aluminum vehicle roof rack, which provides an efficient ground plane for the system. RF and DC power is supplied through the transceiver working from the vehicle battery.
The antenna is fundamentally a parallel tuned LC resonant circuit with the radio attached to a feed-point in the inductive arm from the circuit. The capacitive component is variable and driven by a stepper motor under microprocessor control. Tuning is performed by identifying peak antenna current followed by a VSWR minimisation algorithm.
Together with a high Q, the antenna has low-angle nulls towards the sides, which helps to reduce noise from adjacent sources of interference, eg, the vehicle itself and power lines in its vicinity. As the dominant radiation pattern is directed towards the ionosphere and is fundamentally near vertical incidence sky wave, it overcomes the dead zones, a common limitation of a typical mobile whip antenna. Due to its high efficiency this antenna is effective over short distances. For the search and rescue operations of MCDD, typically the distance between the base and a ‘disaster site’ is around 50 km and is in mountainous terrain.
Currently, MCDD has 64 manpack radios spread countrywide, supported by 20 mobile vehicle stations installed with the Barrett 2018 antenna and 22 fixed base stations, using the Barrett 912 multiwire broadband antennas. At some base stations the HF is also interfaced to the GIRN via a switch to allow interoperability, so an operator can talk to GIRN and relay to HF and vice versa.
Managing director Mr Zakaria Dahili said that “the integration of a reliable HF system for MCDD has been significant. HF is MCDD’s backup to GIRN during remote search and rescue operations.”
Tactical Communications provided local sales, training, maintenance and support to the defence department.
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