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Study of Maximum Usable Frequencies.—On behalf of the Australian lonospheric Prediction Service, this laboratory is making regular measurements of the times when reception of transmissions from Radio Australia cease at night (skip-times). The information is used by the I.P.S. to improve the accuracy of their predictions of the maximum usable frequency for night-time conditions over a distance of 1,500 miles. Radio Research Office. —This office continues to collect and correlate radio research information, and to supply the Navy and the New Zealand amateur radio organization with routine predictions of frequencies for fixed circuits. Since June, 1949, a Cosmic Relations Bulletin has been issued monthly, and is being supplied regularly on request to eighty-four overseas research laboratories. This bulletin contains collected information on radio reception conditions, magnetic and ionospheric disturbances, solar activity, and auroras as observed by co-operating organizations within New Zealand and its dependencies. Microwave Propagation Tests. —The object of these tests is to obtain on behalf of the Post and Telegraph Department operational knowledge of the suitability of 3 cm. and 9 cm. wave-lengths for communicating across Cook Strait in the first instance. A transmitting-station has been established at Blind River, near Seddon, and a receiving-station with continuous recording at Buckley Road, above Island Bay. Continuous records of 9 cm. operation have been obtained since the end of September. The 3 cm. records are rather intermittent owing to instrumental difficulties. ENGINEERING RESEARCH A permanent hydraulics laboratory has been established in one of the large stores buildings near the main laboratory. Earlier work on hydraulic models for the Ministry of Works was carried out in the open, and the new laboratory provides a great improvement in working conditions. Up to four model set-ups can be accommodated at one time, and testing is being carried on by Ministry of Works and D.S.I.R. staffs. Maraetai and Cobb River Spillway Models.—Both of these series of model tests were completed during the year. Maraetai Penstock Models.—Tests are being made to determine whether one of the Maraetai penstocks can take the whole river flow while the diversion tunnel is being plugged and converted into a spillway. Tests on the penstock itself are now complete, and preparations are under way for a further series of tests on the river-bed downstream where the penstock discharges into the river-bed. Roxburg Spillway Models.—A preliminary study of a section through Roxburgh spillway is being made in a glass-sided channel so that flow conditions can be observed and, if faulty, corrected. Preliminary tests have shown modifications to be necessary, and these are being made. Roxburgh Dam and River Models.—This is a study of the whole of the proposed installation at Roxburgh. The model has been completed except for the spillway block. When the latter is installed, tests will be run to check the general performance and flow conditions in the river-bed, in' the diversion channel, and over the spillway.

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