Low altitude f. m. altimeter

Claim 1

IN A FREQUENCY MODULATED RADAR ALTIMETER, A RANDOM NOISE SOURCE, A KLYSTRON OSCILLATOR, MEANS FOR FREQUENCY MODULATING SAID KLYSTRON OSCILLATOR, MEANS CONNECTING SAID RANDOM NOISE SOURCE TO SAID MODULATING MEANS FOR RANDOMLY VARYING THE PERIOD OF THE FREQUENCY MODULATION, A TRANSMITTING ANTENNA CONNECTED TO SAID KLYSTRON OSCILLATOR, A RECEIVING ANTENNA, A BALANCE MICROWAVE MIXER CONNECTED TO SAID RECEIVING ANTENNA, ATTENUATION MEANS COUPLED BETWEEN SAID KLYSTRON OSCILLATOR AND SAID MIXER TO APPLY A PORTION OF THE TRANSMITTED SIGNAL DIRECTLY TO SAID MIXER, SO THAT SAID MIXER PRODUCES A DIFFERENCE FREQUENCY BETWEEN SAID TRANSMITTED SIGNAL AND A RECEIVED SIGNAL REFLECTED FROM THE GROUND WHICH IS PROPORTIONAL TO ALTITUDE, WIDE-BAND AMPLIFYING MEANS CONNECTED TO SAID MIXER, A BALANCED MODULATOR HAVING TWO INPUTS, SAID AMPLIFYING MEANS CONNECTED TO ONE OF SAID MODULATOR INPUTS, A VARIABLE FREQUENCY LOCAL OSCILLATOR CONNECTED TO THE OTHER OF SAID MODULATOR INPUTS, A NARROW BANDWIDTH I.-F. AMPLIFIER COUPLED TO THE OUTPUT OF SAID MODULATOR, A BALANCE F.M. DISCRIMINATOR CONNECTED TO SAID I.-F. AMPLIFIER, MEANS FOR GENERATING A SAWTOOTH VOLTAGE WHEN THE OUTPUT SIGNAL OF SAID DISCRIMINATOR IS ZERO AND FOR AMPLIFYING THE OUTPUTS SIGNAL OF SAID DISCRIMATOR WHEN IT EXCEEDS A PREDETERMINED NEGATIVE MAGNITUDE, MEANS CONNECTED TO SAID LAST-MENTIONED MEANS FOR VARYING THE FREQUENCY OF SAID LOCAL OSCILLATOR IN RESPONSE TO SAID SAWTOOTH VOLTAGE AND FOR LOCKING THE FREQUENCY OF SAID LOCAL OSCILLATOR WHEN THE OUTPUT SIGNAL OF SAID DISCRIMINATOR EXCEEDS SAID PREDETERMINED NEGATIVE MAGNITUDE, ALTITUDE INDICATING MEANS CONNECTED TO SAID DISCRIMINATOR OUTPUT SIGNAL AMPLIFYING MEANS, AND RANGE SELECTING MEANS CONNECTED BETWEEN SAND SAWTOOTH VOLTAGE GENERATING MEANS AND SAID FREQUENCY MODULATING MEANS FOR INCREMENTALLY CHANGING THE AVERAGE MODULATING FREQUENCY OF SAID MODULATING MEANS TO MEASURE ALTITUDES IN A PLURALITY OF DISCRETE RANGES.