AUTOMOTIVE RADIO RUNDOWN NOISE ELIMINATOR

• US 3,761,823 A
• Filed: 07/27/1971
• Issued: 09/25/1973
• Est. Priority Date: 07/27/1971
• Status: Expired due to Term

• Current Assignee: Ford Motor Company
• Original Assignee: Wayne C. Harris
• Inventors: Harris, Wayne C.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Bookbinder, Marc E.
• Application Number:
  US05/166,516
• Time in Patent Office: 791 Days
• Field of Search: 325/312,313,348,362,393,473,478,492,494,422,65,318,319,389,402,399,493 320/40,47,54 334/15 340/248A,248B 328/258,259 307/264,265,320
• US Class Current: 455/297
• CPC Class Codes: H03J 3/185 with varactors, i.e. voltage variable reactive diodes

Abstract

A circuit is incorporated into an electronically tuned radio receiver for eliminating rundown noise. As the power supply voltage in an electronically tuned radio receiver declines, the radio does not merely fade away, it also has its tuning swept thereby producing an undesirable sound, herein termed '"'"''"'"''"'"''"'"'rundown noise.'"'"''"'"''"'"''"'"' This can occur in electronically tuned solid state radio receivers that employ very large power supply filter capacitors which will operate the radio for a short period of time after the primary power supply has been terminated. In automotive systems the existence of an electric-motor-containing accessory, such as a heater or air conditioner, may produce rundown noise. If the motor is running while the radio is in operation, turning the ignition switch off removes power to the system but the electric motor, while coasting to a stop, acts as a d-c generator thereby supplying a declining voltage to the radio. The circuit of this invention terminates radio operation abruptly when the power supply voltage drops below a predetermined value.

Claims

1. In a radio receiver having voltage variable tuning elements, said receiver being subjected to conditions that result in declining supply voltage, said declining supply voltage producing undesirable noise in said receiver as said voltage variable tuning elements are swept during said decline, the improvement comprising:

switching means connected in series with the voltage supply terminals of said receiver so as to terminate operation of said receiver upon actuation of said switching means and responsive to the decline of said supply voltage to a predetermined level for termination by actuation of said switch means the operation of said receiver when said voltage falls to said level.

2. In the receiver of claim 1 wherein said switching means comprises an electrical relay adjusted to drop out at said predetermined level.

3. In the receiver of claim 1 wherein said switching means comprises an electronic switch having a zener diode to establish switching at said predetermined level.

4. In a radio receiver adapted to be connected to a source of voltage which source, when deenergized, continues to supply voltage to said radio receiver At a declining rate for a brief period after deenergization, said receiver employing voltage variable capacitors to effect tuning of said receiver in response to a voltage whose magnitude is a function of the voltage of said source, said voltage variable capacitors producing an undesirable noise in said receiver as they sweep the tuning of said receiver in response to said supply voltage decline, the improvement comprising switching means connected in series between said source and said radio receiver, and responsive to a decline in voltage of said source to a predetermined value, for terminating automatically the operation of said radio receiver.

5. In an automobile radio receiver having terminals adapted to be connected to the electrical system of an automobile, said automobile having, in addition to the conventional battery power supply system, accessories that act as sources of declining potential when disconnected from said battery power supply, said receiver employing a plurality of voltage variable capacitors to effect electronic tuning of said receiver in response to a voltage whose magnitude is a function of the voltage applied to said terminals, said voltage variable capacitors producing an undesirable noise in said receiver when subjected to said declining potential, the improvement comprising switching means connected in series between said terminals and said radio receiver circuits, and responsive to the application of substantially less than normal voltage to said terminals, for terminating automatically operation of said radio receiver.