The invention is an electronic siren comprising in combination circuitry for generating one of a square wave siren and intelligible audio signal and a power output amplifier for audibly reproducing the signal. The amplifier includes transistor circuitry having base, emitter and collector means and a first circuit for coupling the signal-generating circuitry to the base means and one of said emitter and collector means for driving the transistors of the transistor circuitry into saturation in response to the siren signal. The first circuit includes circuitry for applying a dynamic biasing voltage derived from the siren signal to one of the emitter and collector means in phase with the voltage of the siren signal applied to the base means and of a plurality and opposition to the potential drop of the junction of the base means and the other of the emitter and collector means. Speaker circuitry is coupled to the other of the emitter and collector means for audibly reproducing the amplified selected one of the aforesaid signals.

This invention is an electronic siren producing a siren sound having a sound wave produced on a slowly rising and falling frequency. A major cycle is pulsed at intervals with variations in frequency. The variations in each major cycle represent minor cycles. The invention utilizes an electronic circuit to effect such major and minor frequency cycles with existing speaker equipment to project the sound. The electronic circuit includes one or more complex variable rate pulse oscillators wherein the variability of the oscillator is flexible so that it can be programmed internally, or controlled by the speed of the vehicle, or controlled by an operator, or dependent on other circuitry in the unit, or random. The present circuit has for its purpose to combine, superimpose, add, mix, or multiply, various signals from audio sweep oscillators in the circuitry including a plurality of such oscillators with the outputs thereof combined particularly by mixing means which includes multiplexing and simultaneous mixing as well.

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.

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 system 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.

An amplifier particularly suited for amplifying relatively low voltage level siren tone signals in an electronic siren. The amplifier includes an output transformer having first and second primary windings and having a secondary winding for connection to a loudspeaker. Each primary winding is connected during operation between a voltage source and ground and each includes first and second winding sections. Also included are first and second switching devices disposed between the winding sections of the first and second primary windings respectively for opening and closing the circuit between the winding sections of each primary winding in response to the signals which are to be amplified. Circuitry is provided for biasing each output transistor hard off when the other output transistor is conducting. Additional circuitry is provided to enable the amplifier to operate class AB to amplify speech signals.