The 5355A Automatic Frequency Converter when used with a 5356A, 5356B, or 5356C Frequency Converter Head (sold separately), provides pulsed and CW frequency measurement capability to 18/26.5/40GHz for the 5345A Counter. 0.4 to 1.5GHz prescaled input offers pulsed and CW measurement for the lower microwave range even without one of the heads. This is all accomplished while utilizing the 5355A's internal microprocessor which controls the measurement algorithm, computes the input frequency and displays it on the 11-digit 5345A display (sold separately).