US 6,208,848 B1Granted

Radio receiver squelch circuit with automatic adjustment of the squelch threshold

AssigneeGroupe President Electronics

InventorAlbert Bertrana

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Abstract

A radio receiver for receiving audio frequency communications conveyed by a high-frequency carrier and occurring randomly over time. In addition to the tuning circuits, a director, an audio frequency amplifier and a speaker, the receiver includes a controlled switch connected between the detector and the amplifier for disabling or re-enabling the transfer of the audio signal from the detector to the speaker. A filter and second detector set a silence threshold to provide squelch and are arranged to set the silence threshold in accordance with the level of a part of the audio spectrum from the first named detector that contains only noise and is located outside the frequency band of the signal representing the useful audio communication to be received. The receiver is particularly suitable for use in citizen's band equipment.

Claims7

Dependent claims

A radio receiver adapted to receive transmissions comprising a radio-frequency carrier onto which wanted audio frequency communications are amplitude modulated, said receiver including

tuning circuits (1) delivering a frequency spectrum with at least one sideband comprising at least one lobe (L1, L2) delimiting the wanted communications to be received and at least one lobe (L3, L4) containing no information relating to the wanted communications,
at least a first detector (2) supplying an audio frequency signal representing said communications and a first DC voltage representing the level of the received radio-frequency carrier,
means (4) for amplifying said audio frequency signal,
a sound transducer (5) connected to said amplifier means,
switch means (3) connected between said first detector (2) and said amplifier means (4) and adapted to block the passage of said audio frequency signal from said first detector (2) to said sound transducer (5), and
a squelch circuit adapted to generate a signal for controlling said switch means (3) in accordance with a particular squelch threshold,
said squelch circuit including
(i) filter and detector means (12, 13) comprising a band-pass filter connected to a second detector (13) to generate a second DC voltage, and
(ii) means for summing said DC voltages to generate said control signal in accordance with said combination,
the output of said summing means (8) being connected to a comparator (6) also connected to threshold fixing means (7) to produce said control signal by comparison with a predetermined fixed threshold value, wherein
said filter and detector means (12, 13) comprise a band-pass filter (12) tuned to the lobe (L3, L4) containing no information related to wanted communications and which is connected to receive directly said audio frequency signal (AF) from a point downstream of said first detector (2).

8 more elements

Dependencies are inferred from the claim text.