A.F.C. DISABLING CIRCUITRY

• US 3,869,674 A
• Filed: 12/26/1972
• Issued: 03/04/1975
• Est. Priority Date: 12/26/1972
• Status: Expired due to Term

• Current Assignee: Erno Borbely
• Original Assignee: Erno Borbely
• Inventors: Borbely, Erno
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Bookbinder, Marc E.
• Application Number:
  US05/318,345
• Time in Patent Office: 798 Days
• Field of Search: 325/416-423,344,346,453,464,470,473 178/5.8AF 331/16,18,34,36
• US Class Current: 381/3
• CPC Class Codes: H03J 7/10 Modification of automatic frequency control sensitivity or linearising automatic frequency control operation

Abstract

A superheterodyne f.m. receiver having a manually tunable and voltage tunable local oscillator and a ratio detector for providing audio output signal and a.f.c. voltage in response to a received carrier and an a.f.c. channel for conveying the a.f.c. voltage to the local oscillator to maintain precise tuning of the latter, wherein is provided a switch for opening the a.f.c. channel and logic circuitry responsive to the a.f.c. voltage for controlling the switch to open the channel only when (1) the a.f.c. voltage exceeds predetermined levels, and (2) in response to interchannel noise, the a.f.c. channel including a voltage limiter for limiting a.f.c. voltage.

Claims

1. In a frequency modulation receiver having a local oscillator for varying the intermediate frequency output of a mixer, a frequency detector through which said intermediate frequency output is converted into a bipolar a.f.c. signal of a substantially zero output level at the center frequency of a broadcast channel to which the receiver is tuned, means for detecting inter-channel noise, automatic tuning means connected to the local oscillator including an a.f.c. circuit connected to the frequency detector for tracking the zero output level of said a.f.c. signal, logic means connected to the frequency detector for rendering said a.f.c. circuit operative in response to said a.f.c. signal only when said bipolar a.f.c. signal is below a predetermined output level of either polarity representing a relatively wide frequency deviation from said center frequency less than that at which interchannel noise is detected by said means for detecting interchannel noise and otherwise rendering said a.f.c. circuit inoperative, means responsive to said means for detecting interchannel noise for rendering said logic operative to render said a.f.c. circuit inoperative in response to said interchannel noise, and means connected in said a.f.c. circuit for limiting said a.f.c. signal as applied directly to said automatic tuning means to a level substantially less than said predetermined output level.

2. The combination according to claim 1, wherein said interchannel noise is detected at a frequency separation from said center frequency of the order of 200. KHz and wherein said relatively wide frequency deviation is of the order of 80. KHz wide.

3. In a frequency modulation receiver having a local oscillator for varying the intermediate frequency output of a mixer, a frequency detector through which said intermediate frequency output is converted into a bipolar dc a.f.c. signal of substantially zero output level at the center frequencies of broadcast channels to which the receiver is tuned;

automatic tuning means connected to the local oscillator;

a feedback circuit connected between said frequency detector and said automatic tuning means for tracking the zero output level of said dc signal, logic means connected to said frequency detector for rendering said feedback circuit operative in response to said dc signal only while said dc signal is below a predetermined output level of either polarity, inhibit means having an input connected to said detector and an output connected to said logic means for disabling said feedback circuit in response to interchannel noise, and limiting means connected in the feedback circuit for further limiting said tracking thereof to predetermined positive and negative a.f.c. signal levels.

4. The combination of claim 3, wherein said logic means includes a sensing circuit connected to the frequency detector for producing a control signal in response to reception of said a.f.c. signal below said predetermined output level, and switching means connected to the feedback circuit for rendering said feedback circuit operative in response to said control signal to establish frequency deviation limits with respect to said center frequency between which said feedback circuit tracks the zero output level of the audio signal, wherein said frequency deviation limits form a frequency range narrower than said predetermined deviation of said limiting means connected in said feedback circuit.

5. The combination of claim 4, wherein said sensing circuit includes a bipolar sense amplifier having inputs respectively connected to the frequency detector and the inhibit means and an output connected to the switching means.

6. In a frequency modulation receiver, a frequency detector and a reactance tuner responsive to a signal from said detector, said signal approaching zero level when said tuner is tuned to the center frEquency of a broadcast channel, feedback circuit means connected to said detector for automatically tuning said reactance tuner toward said center frequency only while said signal represents predetermined frequency deviation limits from said center frequency, means responsive to said signal only when said signal is above a predetermined level for disabling said feedback circuit, and means responsive to interchannel noise for disabling said feedback circuit.

7. In an f.m. stereophonic receiver having a reactance tuned local oscillator, a mixer responsive to the output of said local oscillator and to a received f.m. signal, an i.f. amplifier responsive to the output of said mixer, and an f.m. detector having an a.f.c. output responsive to the output of said i.f. amplifier, a feedback loop conveying said a.f.c. output to said reactance tuner, said feedback loop including low pass filter means, said feedback loop further including a two-sided limiter in cascade with said low pass filter, whereby the a.f.c. voltage applied to said reactance tuner is inhibited from exceeding pre-determined limits in either polarity, means for sensing whether said a.f.c. voltage falls within or outside of predetermined positive and negative reference values, a grounding switch for said feedback loop, means responsive to said means for sensing for closing said grounding switch while said a.f.c. voltage falls outside said reference values to disable said a.f.c. voltage and for opening said grounding switch while said a.f.c. voltage falls between said reference values to enable said a.f.c. voltage, means for detecting interchannel noise at said f.m. detector, and means responsive to said last means while said last means detects said interchannel noise for turning said grounding switch on.

8. In a frequency modulation receiver having a local oscillator and a mixer providing an i.f. output, a detector responsive to said i.f. output of said mixer for generating a bipolar a.f.c. voltage representing the deviation of said oscillator tuning from a received carrier, an a.f.c. tuner responsive to said a.f.c. voltage and coupled to said oscillator for tuning said oscillator toward said received carrier in such sense as to tend to reduce said a.f.c. voltage to zero, bipolar diode voltage limiting means connected directly to said tuner to limit the a.f.c. voltage applied directly to said tuner to first predetermined positive and negative levels representing a first predetermined frequency difference between said frequency of said local oscillator and said frequency of said received carrier, and disabling means connected to said detector and responsive to said a.f.c. voltage for disabling said a.f.c. circuit in response to said a.f.c. voltage whenever said a.f.c. voltage exceeds second predetermined positive or negative levels representing a second predetermined frequency deviation larger than said first predetermined frequency deviation, and means for disabling said a.f.c. circuit in response to interchannel noise occurring in a band exceeding said second predetermined frequency deviation.

9. The apparatus of claim 8, wherein said a.f.c. tuner includes dc amplifier means having an input connected to said detector and an output connected to said limiting means.

10. The apparatus of claim 9, which further includes means connected to said detector for disabling said a.f.c. tuner by grounding said a.f.c. circuit.

11. The combination according to claim 10, wherein said second predetermined deviation is about 80. KHz and said interchannel noise is at least about 200. KHz above said carrier.