Patent ID: 6208848
Filing Date: 2001-03-27
Classification: H03G

Abstract:
A radio receiver adapted to receive transmissions comprising a radio-frequency carrier onto which wanted audio frequency communications are amplitude modulated, said receiver includingtuning 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), anda 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, whereinsaid 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).