High dynamic range frequency converters for HF and VHF propagation measurments

This paper describes the development of high dynamic range HF and VHF frequency converters for use in propagation measurements. These frequency converters are used to provide variable frequency signal translation from the HF/VHF bands to a digitiser operating at a fixed frequency to perform signal recovery. The frequency converters are required to provide signal translation in the presence of many high level signals from other band users. The range of signal levels that can be accommodated is determined by the noise floor of the system and the maximum level of the unwanted input signals which can be supported without degrading the noise figure due to both third-order distortion products and reciprocal noise mixing between high level signals and the local oscillator phase noise. For this equipment synthesised signal sources with very low close to carrier noise have been developed which should allow high dynamic range to be maintained with small frequency offsets in the presence of high level signals.