3. EQUIPMENT AND INSTRUMENTS 



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receive the data, and the frequencies used 

 are subject to interference by static and other 

 signals. A new system for telemetering the 

 data has been developed using frequency 

 modulation and a challenging signal. In this 

 system each buoy transmits data on the same 

 frequency, but for a limited period of time. 

 A receiver in the buoy responds to an as- 

 signed tone signal from the ship, it turns 

 on the transmitter, selects the top meter in a 

 series, and transmits data from each meter 

 in sequence from top to bottom, and then 

 turns the transmitter off. Although a fre- 



quency of 34.96 megacycles has been per- 

 manently assigned to the Coast and Geodetic 

 Survey, it is necessary to obtain clearance 

 for its used on a regional basis. This fre- 

 quency should not be used unless specifically 

 authorized by the Washington Office. Though 

 the system does not completely eliminate 

 previous difficulties caused by various kinds 

 of radio interference, it has substantially re- 

 duced it, and has eliminated the problems 

 involved in tuning in the various buoy 

 transmitters. 



