Public address/radio switching system
US3938043A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Feb 10, 1975 |
| Grant date | Feb 10, 1976 |
| Priority date | — |
| Expiry date | Feb 10, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B1/20
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.