14. The invention as set forth in claim 12 including switch means connected between said heterodyne detector means and said display means for enabling and inhibiting the application of said video signals thereto, means operated by said first and second pulses for providing a control signal level which enables said switch means in the interval between said first and second pulses and inhibits said switch means in the interval between said second and first pulses whereby to blank said display in the latter interval.
14. The invention as set forth in claim 12 including switch means connected between said heterodyne detector means and said display means for enabling and inhibiting the application of said video signals thereto, means operated by said first and second pulses for providing a control signal level which enables said switch means in the interval between said first and second pulses and inhibits said switch means in the interval between said second and first pulses whereby to blank said display in the latter interval. 15. The invention as set forth in claim 14 wherein said vertical sweep generator includes a first digital to analog converter connected to said second counter for providing as a vertical sweep signal a staircase voltage which increases with increasing counts in said second counter, said fast horizontal sweep generator comprises circuit means for generating a ramp wave which increases in amplitude in the interval between said first and second pulses, and said slow horizontal sweep generator includes a second digital to analog converter connected to said third counter.