Title: Public address/radio switching system

Abstract: Public address add-on circuitry to a conventional radio includes a microphone coupled to a preamplifier which draws significant idle current, and is optimally operable when coupled to a proper load resistance. Permanently affixed and capacitively coupled to the audio input stage of the radio is a series element containing a semiconductor junction device and a resistor selected to properly load the microphone preamplifier. When switching from radio operation to public address the quiescent current of the microphone amplifier reduces the resistance of the junction from a high to a low value thereby allowing the preselected resistor to load the microphone. Semiconductor action further disables the tuner portion of the receiver.

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Inventors: Desai, Samir Thakorbhai (Roselle, IL, US)

Application Number: 548323
Filing Date: 1975-02-10
Publication_date: 1976-02-10
Assignee: Motorola, Inc. (Chicago, IL)
Primary Class(es): 455/335 381/77
Other Classes:
US Patent Ref:

2766378	Oct, 1956	Sundin et al.	179/1.
3365546	Jan, 1968	Kemper	179/1.
3382321	May, 1968	Lybarger et al.	179/1.

Other Refs:
Primary Examiner: Mayer, Albert J.
Assistant Examiner:
Attorney: Gillman; James W., Lisa; Donald J.