Wide operating frequency range superheterodyne fm noise analyzer

Abstract

It is desirable to be able to measure the FM noise spectra of signals whose arrier power is less than the minimum power level at which a direct non-amplified analyzer can operate satisfactorily. Generally a carrier less than approximately + 2 dbm would require analysis by a very low power measuring system. In the superheterodyne analyzer the discrimination process for a high frequency input signal is accomplished at a suitable intermediate frequency. A single set of discrimination equipment is utilized in the measurement of a wide carrier frequency range of input signals using relatively narrow band intermediate frequency hardware to optimize the analysis function. This provides a means for measuring frequencies from 4 GHz to 8 GHz or from 2 MHz to 2 GHz for example, with high accuracy and sensitivity, while using the same intermediate frequency hardware limited to operational bandwidths of a few MHz. A balanced phase detector, power dividers, attenuators coupled with an optimum length transmission line and balanced mixing of signal and reference signals at an IF level coupled with frequency translation provide frequency discrimination over a wide carrier frequency range.