The 548 is a microprocessor-based, heterodyne Microwave Frequency Counter operating from 10 Hz TO 26.5 GHz in three input bands. It features a 12 digit sectionalized LED display that makes it easy to determine frequency. An optional frequency extension (Band 4) and external mixer set permit measurements to 110 GHz in waveguide systems. An optional built-in power meter is available that permits simultaneous frequency and power meter readings with no degradation of the counter specifications.