A Method of Calibrating Standard-Signal Generators and Radio-Frequency Attenuators

The relative magnitudes of radio-frequency signals are measured by passing the signals through a linear heterodyne frequency-convertor and comparing the magnitudes of the resulting intermediate-frequency signals with those of signals from a standard i.f. generator of known performance. Standard-signal generators are calibrated in this way with respect to relatively large fiducial signals. The standard i.f. generator includes an H11-mode piston attenuator excited through a filter designed to reduce errors due to the transmission of energy in other modes. The signals from the frequency convertor and standard generator are compared by means of a linear amplifier with a square-law output meter, which enables accurate measurements to be made with signals below noise level. Signal ratios up to 90 db can be measured directly with the equipment described; the range of indirect measurement is substantially greater. Signal ratios up to 10 db can be measured to 0.02 db, and greater ratios to within 0.2% of their decibel values. Signals 16 db below noise can be measured to 0.5 db. The method has been used at frequencies between 3 and 3000 Mc/s, and can be used for both lower and higher frequencies.