February 1981 | NTIA Technical Report TR-81-63
John R. Juroshek; Frank G. Stewart
Abstract: Interference to radio receivers, such as those used in radio astronomy, can present problems. Adding conventional filters to a radio astronomy receiver's input generally results in an appreciable increase in noise temperature if the filters have any significant losses or if they are not cryogenically cooled. This report takes a cursory look at the possibility of using signal cancellation techniques as an alternate method for eliminating interference in these cases. The technique is particularly suited to interference from the proposed solar-power satellite which would transmit a coherent, cw, microwave, power signal from a geosynchronous satellite. The analysis concludes that a phase-locked loop and associate AGC circuit could be used to generate a replica of the interfering signal which would then be subtracted from the composite signal. The report also concludes that signal suppression of the order of -30 dB should be possible with current technology. The report presents a brief analysis of a second-order, type-one, phase-locked loop. Computer simulation of the loop is shown and tracking errors are assessed for various hypothetical SPS phase perturbations. The report concludes that spectral purity of local oscillators and VCO's will be a major factor in determining the amount of signal cancellation possible with such a scheme.
Keywords: interference; solar power satellite; phase-locked loops; signal cancellation
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