Linear Frequency Sweep Generator for Continuous Transmission FM Sonar.
Patent, Filed 2 Oct 81, patented 9 Aug 83,
DEPARTMENT OF THE NAVY WASHINGTON DC
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A device for producing a varying frequency sine wave synthesized so that the frequency is swept linearly with time for use in a continuous transmission FM sonar. A crystal clock, divider and a 16-bit digital output sweep pointer produce 2 to the 16th power counts for each sweep period Ts. The 2 to the 16th power counts are applied to a 16 bit digital analog converter to provide a highly linear voltage ramp the smoothed result of 2 to the 16th power steps. The ramp is converted to a proportional frequency which is applied to a 5 bit digital counter to access a read only memory programmed to provide a digital to analog converter to produce a voltage output that is a 32 stepped approximation of a sinewave at a frequency which increases between f1 and f2 with linearity of the ramp voltage. A filter smoothes the output.
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