| 摘要 |
<p>A communication system for an emergency vehicle including a provision for selectively producing plural automatically and manually controlled siren sounds, the sound broadcast of radio reception and the sound amplification of the input to a microphone. A complete momentary-contact, pushbutton console may be employed, if desired, by short circuiting all the inputs to ground except that corresponding to the mode of operation selected. Start up instability is also eliminated. A selector pushbutton performs the dual function of manual siren control. Negative feedback from the speaker is provided selectively for radio and public address sytem use. Common use of components reduces cost and complexity. For example, common use of a voltage controlled oscillator, two amplifier stages, a driver and a speaker assembly is made. Radio input is turned on by an alternate action switch. As described in the specification, the action of "turning on" the radio shorts out all siren functions by firing silicon controlled rectifiers. The microphone input is turned on by pushing the "push to talk" switch thereon. This action fires all the siren shorting silicon controlled rectifiers through a pulse amplifier.</p> |
