Muting circuit for a radio receiver

• US 3,939,431 A
• Filed: 11/25/1974
• Issued: 02/17/1976
• Est. Priority Date: 11/25/1974
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Cohlman, Donald C.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Ng, Jin F.
• Application Number:
  US05/526,485
• Time in Patent Office: 449 Days
• Field of Search: 325/313, 325/323, 325/371, 325/377, 325/348, 325/402, 325/456, 325/65, 325/473-478, 179/1 P, 179/1 VL, 179/1 SW, 178/DIG. 12, 328/108-111, 328/165
• US Class Current: 375/217
• CPC Class Codes: H03G 3/342 Muting when some special characteristic of the signal is sensed which distinguishes it from noise, e.g. using speech detector H03G3/344, H03G3/345 take precedence

Abstract

A zero crossing detector and one shot circuit connected to receive audio frequency signals from a receiver and provide a pulse each time the signal crosses a reference level, first and second one shot timers connected to receive the pulses and provide pulses in response thereto which coincide with the zero crossing of a predetermined signal it is desired to mute, coincidence gates receiving the one shot pulses and the delayed pulses and cooperating with a missing pulse detector and a relay in the receiver to mute the receiver whenever the pulses from either of the one shot timers coincide with the pulses from the zero crossing detector, which coincidence indicates a signal of the frequency it is desired to mute.

Claims

1. A method of muting a radio receiver during the reception of audio frequency data or signals of a predetermined frequency, including the steps of:

a. monitoring the audio frequency signals in the receiver and providing a pulse for each zero crossing thereof;

b. using the pulses provided to produce a delayed window subsequent to each pulse, which window is delayed a period equal to the time between zero crossings of data of the predetermined frequency; and

c. comparing the occurrence of the pulses and the windows and muting the receiver for a period longer than the delay between windows each time a pulse and a window coincide.

2. A circuit for muting a radio receiver during the reception of data or signals of a predetermined frequency, said circuit comprising:

a. input means for receiving audio frequency signals from the radio receiver;

b. zero crossing detector means connected to receive the audio frequency signals from said input means and supply an indicating pulse each time the amplitude of the audio frequency signals passes through a reference level;

c. one shot timer means connected to receive the indicating pulses from the zero crossing detector means and supply a timing pulse a first predetermined time after the reception of each indicating pulse, the first predetermined time corresponding with a period between zero crossings of the predetermined frequency, and the timer means being reset when a second indicating pulse is applied thereto subsequent to a first indicating pulse and before the first predetermined time has elapsed;

d. coincidence gate means coupled to said zero crossing detector means and said timer means for supplying an output pulse each time an indicating pulse and a timing pulse are coincidentally supplied thereto;

e. missing pulse detector means connected to receive the output pulses from said coincidence gate means and supply a muting signal during the reception of a series of the output pulses, said missing pulse detector means providing an unmuting signal a second predetermined time after the reception of the last output pulse in the series, said second predetermined time being longer than said first predetermined time; and

f. switch means coupled to said missing pulse detector means and said receiver for receiving the muting and unmuting signals and muting the receiver in response to the muting signal and unmuting the receiver in response to the unmuting signal.

3. A circuit for muting a radio receiver as claimed in claim 2 including an activity and quieting detector connected to receive indicating pulses from the zero crossing detector and quieting signals from the receiver and supply an output signal in the absence of both the pulses and the quieting signals, and an OR gate connected to receive the output signal from said activity and quieting detector and the muting signal from the missing pulse detector means and supply a muting signal to the switch means.

4. A circuit for muting a radio receiver as claimed in claim 2 including in addition latch means associated with the missing pulse detector means and coupled to receive a quieting signal from the receiver, said latch means operating to prevent said missing pulse detector from supplying a second muting signal subsequent to a first muting signal and during the presence of a quieting signal.

5. A circuit for muting a radio receiver as claimed in claim 2 wherein the switch means includes a relay.

6. A circuit for muting a radio receiver as claimed in claim 2 wherein the zero crossing detector means includes an amplifier and limiter for converting the audio frequency signals to square wave signals.

7. A circuit for muting a radio receiver as claimed in claim 6 wherein the zero crossing detector means includes in addition a one shot circuit that provides a relatively short indicating pulse at the beginning and end of each square wave and which supplies the indicating pulses to the one shot timer means.

8. A circuit for muting a radio receiver as claimed in claim 2 wherein the one shot timer means includes a first and a second one shot timer each having an input coupled to receive indicating pulses from the zero crossing detector means and an output supplying timing pulses to the coincidence gate means, the first timer supplying a timing pulse subsequent to receiving an indicating pulse a period of time equal to the time between the first and second zero crossings of a cycle of the signal having the predetermined frequency, and the second timer supplying a timing pulse subsequent to receiving an indicating pulse a period of time equal to the time between the second and third zero crossings of a cycle of the signal having the predetermined frequency.

9. A circuit for muting a radio receiver as claimed in claim 8 wherein the coincidence gate means includes first and second AND gates and an OR gate, said first AND gate being connected to receive timing pulses from the first timer and indicating pulses and supplying coincidence pulses to said OR gate, said second AND gate being connected to receive timing pulses from the second timer and indicating pulses and supplying coincidence pulses to said OR gate, and said OR gate supplying output pulses to the missing pulse detector means.