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03 August 2011

RaDAR – disaster relief communication?

In this monthly feature, Hans van de Groenendaal ZS6AKV, executive chairman of the South African Amateur Radio Development Trust (SAARDT), looks at various technologies and activities that drive amateur radio. SAARDT is dedicated to the development of amateur radio in South Africa with a special interest in the youth. The organisation is funded by donations and supports the South African Radio League and SA AMSAT.

RaDAR is not radar in the traditional sense of the word. Radar mainly refers to the detecting of distant or approaching objects. Rapid deployment amateur radio (RaDAR) refers to the flexibility to enable radio communication under difficult conditions, without external resources. It's about practising communication as a radio amateur in many different circumstances and in many different ways. RaDAR is a way of life and being ever-ready, so that rapid deployment becomes second nature no matter what the circumstance. In short, RaDAR is rapidly deployed, easily movable (objects), amateur radio stations.

It started some years ago as a fun project which was called a "shack in a sack" – meaning taking a packfull of radio equipment to an outdoor location in a park, a field or a mountain top, setting up and participating in a field day contest. "Shack "is an in all encompassing slang word for a roomfull of radio equipment. It found its first use amongst the early radio experimenters at the turn of the previous century when equipment was very large, cumbersome and mostly installed in an outbuilding. The objective of the contest is to make as many two-way contacts as possible, scoring points for different categories such as distance, with stations outside South Africa, contact with a fixed station or a mobile station or a contact with a person driving around town.

The whole idea of rapid deployment mobility caught the imagination of Eddie Leighton from Lichtenburg. His amateur radio call sign is ZS6BNE. Being a long distance runner he saw the opportunity to combine his running sport with his interest in radio and set out to expand the concept by getting more people involved. The name "shack in a sack" did not appeal to him so he proposed RaDAR and that is what it is known as today.

Competitions are held regularly and to be considered as a true RaDAR station the entire station equipment, radios, batteries, mast, antennas and refreshments must be easily portable. The participant is required to walk, carrying his equipment, for at least one kilometre prior to setting up the station. This may sound easy but Eddie says there are several challenges of which keeping the backpack weight down is perhaps the major one. It calls for some real innovation. One of the other challenges is the antenna, particularly if the participant includes satellite operation.

One of the obvious weight savers is to dispense with a portable mast and to look for a natural support like a large tree and then the type of antenna and feed line is another important consideration. By incorporating an antenna tuner in the set-up, a long wire antenna, a balun with a short piece of coaxial cable can be used which is easy to get up into a tree and tuned to resonate on the required frequency providing a good impedance match for the transceiver. Eddie devised a camera tripod stand that houses the satellite antenna and a hook-on platform for the radio and antenna tuner. A netbook PC is used for tracking satellites and is also used for digital communications, using the sound card interfaced to a shortwave radio.

On HF he uses a tiny Yaesu FT-817ND which has a built-in battery pack and covers the 160 – 10 m amateur HF bands as well as 50, 144 MHz amateur VHF frequencies and 430 MHz amateur UHF frequencies. It delivers a maximum output of 5 W which provides an extra challenge in the RaDAR contests. Higher points are allocated to stations using such low power. Eddie also has had some remarkable results using the Arrow 70 cm/2 m crossed yagi antenna for communications using several amateur radio satellites including the SumbandilaSat amateur transponder designated internationally as SO67. Currently he is experimenting with a 70 cm /2 m vertical whip as it is lighter and smaller to carry.
He admits that you have to be fit to carry the backpack and rapidly deploy the equipment. The South African Radio League’s disaster communication group, HAMNET have shown interest in the RaDAR concept. During the recent Japanese Tsunami disaster rescue operation, amateur satellite store and forward facilities on the International Space Station proved a useful addition to the communications network – another possible communication niche for RaDAR. South Africa will host the Global Amateur Radio Emergency Communications meeting in August 2011, when Eddie will demonstrate the RaDAR concept, concentrating on digital communications in the field.

Pictured: Eddie Leighton ZS6BNE setting up the satellite antenna on the modified camera tripod. His grandson takes a great interest in ham radio activity.

- EE-Publishers