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Este vorba de: John Rabson G3PAI
LIMES FARM HOUSE EYKE WOODBRIDGE
Eyke, WOODBRIDGE IP12 2QG
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Mare le Bas
Tel. 03 86 20 2550
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73 & GL
Icom have recently supported a series of underground propagation tests taking part in the Standedge tunnels between Manchester and Sheffield on the 25th April 2004. The purpose of the tests was to find out what sort of range could be achieved in the tunnel without using repeaters or talk-through units. The company supplied an IC-910H UHF transceiver to aid the test.
The propagation tests were run by a mixed party of Cave Radio and Raynet people and in conjunction with Network Rail. John Rabson G3PAI Cave Radio & Electronics Group and Suffolk Raynet said, 'Previous tests at VHF and UHF have indicated that higher frequencies give greater range, but far less than we could expect in free space. At VHF the best we could achieve was only a few hundred metres. Using PMR 446 handhelds with a nominal range in open country of 3 km, we have achieved a range in the tunnel of 1km. It therefore seemed worth trying 1.3GHz to see how far we can get. As the tunnel is nearly 5km long, a range of 2-1/2km would allow us to communicate with anywhere in the tunnel from one or other portal.'
John Rabson G3PAI said, 'I managed to borrow a IC-T81 handheld from a local microwave enthusiast. I had to find another radio to allow me to do these tests so I was very pleased when Icom stepped in and supplied me with an IC-910H.'
He added, 'The tests were a success. With about 1W output from the transmitter at each end we communicated right through the 5-km length of the tunnel and signals were still S9+60dB on the 910. Moving about 10 or 20 m out of the tunnel at both ends simultaneously, signal strength was down to about S7 but copy was still perfect.'