US 4,045,741 AGranted

Scanning receiver for use in a tour guide system

OwnerJohn V. Missaleinventor

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Abstract

A tour guide system includes a radio receiver section adapted to receive a plurality of preselected signal frequencies and an automatic frequency selecting means for tuning the receiver only to one of the preselected frequencies whose signal strength exceeds a predetermined amplitude. The receiver section essentially comprises an antenna stage, a tuning stage, a signal amplitude detecting stage, an expander stage, and an audio transducer stage. The automatic frequency selecting means comprises a level detector having an input connected to the output of the receiver detector stage, an astable multivibrator having an input connected to the output of the level detector, a shift register having an input connected to the output of the astable multivibrator and having a plurality of output of each stages, each connected to a field effect transistor (FET) in the tuning stage of the receiver. The tuning stage of the receiver comprises a plurality of capacitors and FET's in parallel with a common inductance. In operation, the astable multivibrator causes the shift register to activate the FET's in such a fashion that the receiver searches for a frequency having a signal strength exceeding a predetermined value. When a frequency is found, the level detector causes the astable multivibrator to cease oscillating, thereby locking the receiver to the predetermined frequency as long as the amplitude of that frequency exceeds the certain predetermined value.

Claims9

Dependent claims

An improved portable radio receiver for receiving a plurality of preselected frequencies, said receiver comprising:

an antenna for receiving said pre-selected frequencies;
a tuning means comprising a tank-type resonant circuit including at least one inductance and at least a plurality of capacitance elements connected therewith, said tuning means being connected to said antenna;
a detecting means for detecting signals from said tuning means;
and,
an audio transducer stage for producing an audio output in response to the output of said detecting means;
and,
an automatic frequency selecting means for scanning said pre-selected frequencies and for automatically tuning said receiver to the first one of said pre-selected frequencies whose signal strength exceeds a predetermined amplitude, said automatic frequency selecting means including:
a level detector for providing a specified output whenever the amplitude of the signal received from the detecting means exceeds a predetermined threshold;
an oscillator having an input connected to the output of said level detector;
a counter circuit comprising a shift register having a plurality of outputs, each output corresponding to a stage of said shift register, said counter circuit having an input connected to the output of said oscillator;
a switching means comprising a plurality of switch means each having an input connected to one of said outputs of said counter circuit, said switching means comprising a plurality of field effect transistors, each of which is connected to one of said capacitive elements of said tank circuit, said switching means being connected in circuit with said tuning means;
and,
a delay means for loading a beginning bit into said shift register after said receiver has been turned on.

10 more elements

Dependencies are inferred from the claim text.