Nonquantized Frequency-Modulated Altimeter

A new principle that makes possible nonquantized altitude information so that the accurate range of altimeters can be extended to include low-level operation is described. A frequency shifter is inserted between the local oscillator and the mixer in order to remove the inherent error in conventional altimeters that makes them objectionable for low-altitude operation. The authors show how the characteristic of the amplifier can be shaped diferently and point out that the strength of the return signal and the inherent amplitude modulation determine the most suitable characteristic for any particular operating condition.