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| Digital interface circuit |
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| Encryption apparatus, cryptographic communication system, key recovery system, and storage medium |
| OF THE INVENTION A preferred embodiment of the present invention will now be described. In the ... |
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| Broadcast receiver |
| OF THE PREFERRED EMBODIMENT Using the antenna 1, a sterophonic broadcast signal is received, the ... |
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| Electronic reverberation device |
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| Auscultation augmentation device |
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| Cryptographic key, or other secret material, recovery |
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Dual indicator circuit for tuning and stereo signals
| Details |
Inventors: Ecklund, Lawrence M.;
Assignee: Motorola, Inc. (Schaumburg, IL)
Primary Examiner:
Assistant Examiner:
Attorney, Agent or Firm:
In a stereophonic broadcasting receiver, a single indicator with two levels of illumination serves to provide indication of both accurate tuning and the presence of stereophonic signals. One signal or a combination of signals related to the tuning circuits of the receiver cause the indicator to be illuminated to a perceptible level. When, by use of a pilot tone detector, it is certain that stereophonic signals are being received, additional current is caused to flow through the indicator, raising the illumination to the maximum allowable level. The circuit has particular application to manually tuned receivers. |
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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIG.
1 is a highly simplified block diagram of a receiver for use in receiving amplitude modulated stereophonic signals.
The receiver could be any one of many such receivers presently known, and the received AM stereo signals could have been modulated in any one of the modulation formats presently known as long as they include a subaudible stereo presence tone when stereophonic signals are being broadcast.
Thus, the signals will be received at an antenna 10 and processed in an RF/IF stage 12.
A tuning detector 14 is coupled to some portion of a decoder and audio circuit 15 which will have a signal present only when the receiver is locked in on a station or is within a given tuning "window".
The tuning detector 14 could, in some circumstances, be coupled to a corresponding output of the RF/IF stage 12.
The output of the tuning detector will be coupled, through a resistor 16 or other current limiting device, to an LED 18 which is connected through a resistor 20 to a source of power 22.
The particular circuit of the decoder portion of the circuit 15 will depend on the modulation format of the received signals.
There are at least five different AM stereophonic broadcasting systems and each of them utilizes a low frequency or subaudible signal modulated onto the stereo (L-R) channel for use in indicating the presence of stereo signals.
The stereo and audio circuits 15 are coupled to a pair of speakers 26 and also to a stereo detector and control circuit 28.
Again the specific circuitry of the circuits 28 will depend on the particular signals received.
An output of the detector control circuit 28 is coupled back to the decoder and audio circuits 24 for activating the stereo portion of the output when a pilot tone is present.
The output of the detector control circuit 28 is also coupled to the LED 18.
In operation, there will be an output signal from the tuning detector 14 only when an AM station has been tuned in accurately by means of a tuning knob, pushbutton, or similar tuning means 30
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Audio Signal Processing 
