| 摘要 |
PURPOSE:To prevent the fact that sweep is stopped by mistake due to a spurious signal, etc., by raising a muting level in an automatic sweeping state. CONSTITUTION:A muting level setting circuit 12 mutes a low frequency amplifier 7 in case of an input signal which is below a set level. In case when there is an input signal exceeding the set level, a receiving signal is supplied to a loud speaker, also a stop signal generating circuit 11 is driven by a muting control signal from a detector 5, a stop signal is inputted to a PLL controller 9, and the automatic sweep is stopped. The muting level is set in advance so as to be switched by being interlocked with changeover of one-step sweep and automatic sweep. At the time of automatic sweep, the level is set so that muting is not turned off against a weak input such as a spurious signal, etc. |
