Advanced Digital Signal Processing Techniques and Hardware for Radio Direction Finding Applications

A dual-channel Digital Signal Processing-based IF Processor (DSPIFP) has been developed for use in radio direction finders. An undersampled mixing technique was used to allow direct digitization at 25 kHz of a 455 kHz IF signal with a bandwidth of 10 kHz or less. A 64-point FFT was used to estimate the spectrum. The DSPIFP measures amplitudes from both channels and relative phase difference between channels. These measurements are made on the strongest signal in the passband; however, this could be extended to other resolved signals in the passband. The test results have shown that DSP techniques can be used to provide IF processing functions previously implemented in analog circuitry, giving comparable performance. The DSPIFP has the additional capability of effective amplitude and phase measurement on the desired signal in the presence of co-channel interference.