VHF and UHF Attenuation Measurements to 140 dB

A system has been assembled for rapid comparison of production step attenuators, with a reference attenuator using direct substitution at spot frequencies in the VHF and UHF range. The total attenuation range for such tests is 140 dB, with a basic resolution of ±0.01 dB and with maximum errors of ±0.08 dB, attributable, primarily, to reflection inaccuracies. Simplified methods for measurement to 110 dB at any selected frequency are described, as well as additional refinements permitting spot frequency measurements to 170 dB. The basic equipment required for these measurements is a well-shielded signal source generating in excess of 100 mW, and a low-noise narrow-band receiver with provision for locking the signal frequency to the center of the receiver passband.