It is shown that the f ( f ) characteristics of a HBT DRO can be approximated using the HBT's low frequency noise spectra and the oscillator's upconversion factor, Experimental studies have been used for this purpose and the measured f ( f ) ranged -89dBc/Hz to -10ldBc/Hz at a lOkHz offset frequency (-124dBc/Hz best performance at 100kHz). It was shown that the upconversion of the low frequency noise is the primary cause of f ( f ) in the oscillator and its frequency dependence is directly impacted by the low frequency noise spectrum rather than IC;M itself. dE(f)/df deviates from the -3OdB/decade rate, expected for upconversion of ideal l/f noise, due to traps in the device.