| 摘要 |
PURPOSE:To improve S/N and also to prevent a malfunction due to noise for a receiver by transmitting first a reference frequency then the signal containing information, and detecting the first reference frequency by a frequency analyzing circuit at the receiver to control a local oscillation circuit so that the reference frequency is set at a point near the center of the band of an intermediate frequency amplifier circuit. CONSTITUTION:The output signal of a tone generating part 15 is converted into a frequency and supplied to a frequency analyzing circuit 20. A signal corresponding to a reference frequency f0 is first outputted from one of filters of filter groups 20a, 20b... and supplied to an information decoding circuit 21. The circuit 21 dfines the signal supplied first as the frequency f0 and controls a local oscillation circuit 8. Thus the signal corresponding to the frequency f0 is set at a point near the center of the band of an intermediate frequency amplifier circuit 10. Then a comparator 22 checks whether or not the signal corresponding to the f0 is generated at the point near the center of band of the circuit 10. Thus it is possible to prevent a discriminating error due to noise, etc. to the reference frequency. |
