A digital frequency upconversion and downconversion scheme for receivers and transmitters enables high resolution downconversion and upconversion, respectively, with low phase noise. A digital signal processor (DSP) (230) receives temperature measurement information from a temperature transducer associated with a reference oscillator (240), and also receives channel tuning and other information. The DSP adjusts the signal samples accordingly, without adjusting the operation of the oscillator. Additionally, the inventive filtering scheme, preferably implemented in an application specific integrated circuit (ASIC), receives digital filtering coefficient information, digital symbol timing phase control signals, and, in some cases, other information from the DSP. As a result, the scheme enables operation at 1 Hz resolution, with phase noise which is at least 33.5 dB down at 10 Hz in the case of downconversion, and at least 42 dB down at 10 Hz in the case of upconversion.