The 5342A Microwave Frequency Counter measures the frequency of signals in the range of 10 Hz to 18 GHz, with a basic sensitivity of -25 dBm. Signals in the frequency range of 10 Hz to 500 MHz are measured by the direct count method. Signals in the frequency range of 500 MHz to 18 GHz are down-converted to an IF by a heterodyne conversion technique for application to the counter circuits. The unique conversion technique employed results in high sensitivity and FM tolerance in addition to automatic amplitude discrimination. The counted IF is added to the local oscillator frequency to determine the unknown frequency for display.