| 摘要 |
PURPOSE:To decrease the code error rate of a main signal by switching a frequency band of a PLL loop narrower or broader based on sub-signal transmission information included in a demodulated main signal to improve the C/N when no sub-signal is transmitted. CONSTITUTION:When a sub-signal shown in (2) is used and a frequency signal to be modulated shown in (3) is subjected to FM modulation, sub-signal transmission information is added to a main signal shown in (1) and the added main signal and the said sub-signal radiates a modulation frequency signal shown in (4) subjected to FM composite modulation is radiated in a form of a radio wave. Thus, the sub-signal transmission information added to the main signal is detected at the reception side and it is possible to change over the frequency band of the PLL loop to obtain the optimum C/N stably. A changeover switch 2-4 shown in a figure based on a control signal shown in (8) extracted by the sub- signal transmission information, the frequency band of the PLL loop consisting of a PLL2-3 is widened (when the sub-signal is included) or narrowered (when the sub-signal is not included). |
