Analysis of Errors in a Phase-Shift Angle Telemetering System

Abstract

The author presents results of an investigation of errors in a phase-shift telemetering system. In evolving a method to transmit angular position data, the selection of electrical phase angle to represent the desired data is a natural one, since there is a great deal of similarity between the two quantities. Since phase shift is a relative quantity, it is necessary to transmit a reference signal as well as a phase-shifted signal; and in order to transmit both of these on a common carrier, and to avoid angular ambiguities, the phaseshifted wave is transmitted at some integral multiple of the reference frequency. At the receiver, the frequency of the reference wave is multiplied prior to comparison with the phase-shifted signal. Minimum bandwidth is required when the integral multiple is 2, and it is with this particular system (which is perhaps the most common of all) that the following discussion of errors is concerned, although the analysis made for this case may be extended to others as well. This method has been successfully applied in plane-toground telemetering and in the relaying of shaft-position data in general. It is pointed out that the basic telemetering system will be of doubtful value when long-distance transmission is required, because of the distortion and error introduced by multipath propagation.