Frequency adjusting arrangement

In a radar receiver wherein a voltage controlled oscillator is used to produce a local oscillator signal to be heterodyned with a radar signal to form an intermediate frequency signal for detection in a phase detector, such detector producing a first alternating signal having a frequency indicative of the difference between the actual frequency of the voltage controlled oscillator and the frequency of such oscillator required to produce the intermediate frequency signal, the improvement comprising:

• (a) a high pass filter, responsive to the alternating signal from the phase detector, for isolating such signal;
• (b) means, responsive to the local oscillator signal out of the voltage controlled oscillator, for producing a second alternating signal indicative of the difference between the actual frequency out of the voltage controlled oscillator and a reference frequency;
• and
• (c) means, responsive to the first and second alternating signals, for changing the frequency of the voltage controlled oscillator to null the first alternating signal.