C/N DETECTING DEVICE FOR RECEIVE SIGNAL AND SATELLITE TRACKING SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide a C/N detecting device (C/N: signal-to-noise ratio) to detect the ratio C/N of a specific signal included in a receive signal and a noise signal by using one band-pass filter without changing the direction of an antenna. SOLUTION: To detect the C/N of a beacon signal from an artificial satellite used for satellite tracking by an on-vehicle satellite tracking system, the channel selecting circuit composed of a mixing circuit 56 and a crystal filter 64 is enabled to select the channels of the beacon signal and a noise signal respectively and a microcomputer 70 switches the oscillation frequency of a local oscillation circuit 58 outputting a local oscillation signal to the mixing circuit 56 in order through PLL circuit 60. Then the microcomputer 70 detects the signal level at every signal channel selection time associatively with the mentioned switching operation and calculates the C/N from detected signal levels. Consequently, the C/N can be detected by using one filter without changing the direction of the antenna.