FM altimeters
FM is a common abbreviation used in radio technology, which describes the modulation frequency. FM radar altimeters have, which does not send a single pulse, only a continuous electromagnetic wave, and the broadcasting and receiving antennas are independent. Transmitted signal is modulated so that its frequency is increasing at a known rate. As a result, the reflected signal is received, it is lower than the frequency signal is sent. As a result, the device can distinguish between broadcast and receive signals. The difference frequency signal corresponds to a shift in time between the giving and receiving a signal in proportion to the altitude to be calculated automatically.