Fm stereo receiver having automatic threshold switching circuitry

Claim 2

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder and dual channel audio amplifier, the combination of tuning responsive means for producing a control signal representative of a condition of detuning, means including a band pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, first switching means in the decoder for establishing whether the signal is fed to the audio amplifier in the stereo or monophonic mode, second switching means for selectively squelching the signal in the audio amplifier, and means jointly responsive to the increasing level of the control signals for operating said switching means in sequence.

Claim 3

The combination as claimed in claim 1 in which the means jointly responsive to the level of the control signals includes separate adjustable controls for setting the stereo and squelch threshold conditions.

Claim 4

The combination as claimed in claim 1 in which the band pass noise filter is constructed and arranged to pass noise components having a frequency in excess of the intelligence-conveying frequencies in the waves received by the receiver.

Claim 5

The combination as claimed in claim 1 in which the band pass noise filter is constructed and arranged to pass noise frequency components in the neighborhood of 100 kHz.

Claim 6

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder and dual channel audio amplifier, the combination of means for producing a control signal representative of the degree to which the signal passing to the audio amplifier is substandard, first switching means in the decoder for establishing whether the signal is fed to the audio amplifier in the stereo or monophonic mode, second switching means for selectively squelching the signal in the audio amplifier, means responsive to a first threshold level of control signal for operating said first switching means for feeding of the signal in the monophonic mode, and means responsive to a higher threshold level of control signal for operating the second switching means for squelching of the signal.

Claim 7

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder and dual channel audio amplifier, the combination of means for producing a control signal representative of the degree to which the signal passing to the audio amplifier is substandard, first switching means in the decoder for establishing whether the signal is fed to the audio amplifier in the stereo or monophonic mode, second switching means for selectively squelching the signal in the audio amplifier, means responsive to a first threshold level of control signal for operating said first switching means for feeding of the signal in the monophonic mode, and means responsive to a higher threshold level of control signal for operating the second switching means for squelching of the signal.

Claim 8

The combination as claimed in claim 5 including means associated with at least the second switching means for lowering the switching threshold automatically during the time that the switch is in its switched condition thereby to maintain the switching means in such switched condition notwithstanding moderate subsequent reduction in the level of the control signal to a point below the initial threshold to inhibit repeated switching back and forth under marginal conditions of control signal.

Claim 9

In an FM receiver having an R. F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector and audio amplifier, the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, switching means for selectively squelching the signal in the audio amplifier, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, and means responsive to the control signal for operating the switching means to prevent reproduction of a signal by said amplifier which is detuned or which is accompanied by high frequency noise

Claim 10

In an FM receiver having an R. F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector and audio amplifier, the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, switching means for selectively squelching the signal in the audio amplifier, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, and means responsive to the control signal for operating the switching means to prevent reproduction of a signal by said amplifier which is detuned or which is accompanied by high frequency noise

Claim 11

In an FM stereo receiver having an R. F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder and dual channel audio amplifier, the combination of tuning-responSive means for producing a control signal representative of the degree of detuning, means including a band pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, first switching means for selectively squelching the signal in the audio amplifier, second switching means in the decoder for determining whether the signal is fed to the audio amplifier in the stereo or monophonic mode, means for coupling the control signals to the switching means, and means associated with each of said switching means for adjusting the level of control signal at which switching takes place.

Claim 12

In an FM stereo receiver having an R. F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder and dual channel audio amplifier, the combination of tuning-responSive means for producing a control signal representative of the degree of detuning, means including a band pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, first switching means for selectively squelching the signal in the audio amplifier, second switching means in the decoder for determining whether the signal is fed to the audio amplifier in the stereo or monophonic mode, means for coupling the control signals to the switching means, and means associated with each of said switching means for adjusting the level of control signal at which switching takes place.

Claim 13

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector and audio amplifier, the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band-pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, switching means for selectively squelching the signal in the audio amplifier, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, means responsive to the control signal''s reaching a predetermined threshold level for operating the switching means to prevent reproduction of a signal by said amplifier which is detuned or which is accompanied by noise, said responsive means including means for establishing a condition of hysteresis to inhibit return to the unsquelched condition, thereby to prevent repeated switching between the squelched and unsquelched condition upon variations in signal noise level.

Claim 14

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector and audio amplifier, the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band-pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, switching means for selectively squelching the signal in the audio amplifier, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, means responsive to the control signal''s reaching a predetermined threshold level for operating the switching means to prevent reproduction of a signal by said amplifier which is detuned or which is accompanied by noise, said responsive means including means for establishing a condition of hysteresis to inhibit return to the unsquelched condition, thereby to prevent repeated switching between the squelched and unsquelched condition upon variations in signal noise level.

Claim 15

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder, and dual channel audio amplifier the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band-pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, first switching means associated with the decoder for switching from stereo to monophonic reproduction in the audio amplifier, second switching means for selectively squelching the signal in the audio amplifier, means responsive to the control signal''s reaching respective threshold levels for operating the first and second switching means, said first and second switching means each having means for establishing a condition of hysteresis to inhibit return to the initial condition, thereby to minimize switching back and forth under marginal conditions of control signal.

Claim 16

In an FM stereo receiver having an R.F. stage, tunable local oscillator, mixer, I.F. amplifier, ratio detector, decoder, and dual channel audio amplifier the combination of tuning-responsive means for producing a control signal representative of the degree of detuning, means including a band-pass noise filter for producing a control signal representing the amount of high frequency noise in the output of the ratio detector, means for combining the signals from the tuning responsive means and noise filter means to produce a control signal, first switching means associated with the decoder for switching from stereo to monophonic reproduction in the audio amplifier, second switching means for selectively squelching the signal in the audio amplifier, means responsive to the control signal''s reaching respective threshold levels for operating the first and second switching means, said first and second switching means each having means for establishing a condition of hysteresis to inhibit return to the initial condition, thereby to minimize switching back and forth under marginal conditions of control signal.

Claim 17

In an FM stereo receiver having a tunable R.F. stage, local oscillator, mixer, I.F. amplifier, ratio detector, decoder, and dual channel audio amplifier, the combination of means responsive to a substandard signal at the output of the ratio detector for producing a disabling control signal, switching means for selectively squelching the signal in the audio amplifier, means for coupling the control signal to the switching means for selectively squelching the signal in the audio amplifier, detecting means for detecting the reception of a monophonic signal, and means including a selectively actuatable ''''stereo only'''' switch for coupling the output of the detecting means to the switching means so that all incoming signals other than stereo signals are effectively squelched.

Claim 18

In an FM stereo receiver having a tunable R.F. stage, local oscillator, mixer, I.F. amplifier, ratio detector, decoder, and dual channel audio amplifier, the combination of means responsive to a substandard signal at the output of the ratio detector for producing a disabling control signal, switching means for selectively squelching the signal in the audio amplifier, means for coupling the control signal to the switching means for selectively squelching the signal in the audio amplifier, detecting means for detecting the reception of a monophonic signal, and means including a selectively actuatable ''''stereo only'''' switch for coupling the output of the detecting means to the switching means so that all incoming signals other than stereo signals are effectively squelched.