Jean E. Adams et al.

Abstract: In order to determine the feasibility of multiple system decoders for AM stereo receivers, the Institute for Telecommunication Sciences made a series of laboratory and field tests on certain commercially available AM stereo receivers. We also made tests that used an IC test set in order to directly compare the performance of a multiple system AM stereo decoder IC with the best available single system decoder IC. We have described the tests in detail that show the relative performance of the multiple system receivers to the performance of single system receivers. In analyzing the data, we have compared distortion, signal-to-noise ratio, and stereo detection capabilities of the receivers. These data were measured over a full range of audio frequencies from 50 to 10000 Hz, both without any interfering signals, and with interference. The interference was at both lower and upper adjacent channel frequencies and precisely offset from the desired carrier frequency by 15 and 25 Hz. We measured receiver performance, and obtained data for 3 levels of desired carrier amplitude, 3 levels of modulation, and for the full combination of stereo audio channel matrices. The analysis of these measured data show that multiple system ICs and the single system ICs perform comparably in the direct IC comparison. In addition, the IC test set receiver operating with the multiple system decoder compares favorably with the best high quality automobile receiver tested that uses a single system decoder IC. We have concluded that multiple system decoders are technically feasible and can function as well as the best currently available single system decoders. We found that one manufacturer has developed a multiple system decoder on a single IC that compares favorably with all of the existing single system decoders that were tested.

Keywords: radio; measurements; AM broadcasting; AM stereo; signal-to-interference

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