US 4,397,040 AGranted

UHF Receiver with decreased distortion due to multipath reception

AssigneeBlaupunkt-Werke GmbH

InventorsPeter Jandel, Klaus Vathauer

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Abstract

In a UHF receiver in which volume control is carried out as a function of received field strength, distortion due to multipath reception is prevented by use of a band-pass filter connected to the output terminal of the IF section which furnishes a signal indicative of received field strength. The low frequency noise signals appearing at this terminal in the presence of multipath reception are passed by the band-pass filter and subsequently rectified to create a DC control signal which closes a switch. This in turn increases the time constant of the connecting circuit between the field strength output terminal and the control input of the volume control circuit. The increase in time constant suppresses the above-mentioned low frequency oscillations which occur only during multipath reception, so that the output of the volume control circuit is not affected by such multipath reception.

Claims5

Dependent claims

In a UHF-FM receiver, particularly FM car radio, having

an intermediate frequency (IF) section including
amplitude demodulator means (17) having an output (14) strength signal indicative of the field strength of the signal received by said receiver, said field strength signal having amplitude modulation superimposed thereon only in the presence of multipath reception and automatic volume control means (19) having a signal input connected to said IF section and a control input;
and means (22, 23-26) for connecting said control input of said volume control means to said output (14) furnishing said field strength signal, said connecting means including means (25, 26) for establishing a predetermined time constant;
apparatus (27) for detecting multipath reception and furnishing a multipath signal indicative of said multipath reception connected to said demodulator means output (14), comprising
band-pass filter means (34) connected to said amplitude demodulator means for furnishing a filter output signal only in response to a field strength signal having said amplitude modulation;
and
rectifier means (35) connected to said band-pass filter means and having a multipath signal output (29) for furnishing said multipath signal in response to said filter output signal;
and
means (32, 33) connected to and controlled by said rectifier means (35) for increasing the time constant of said connecting means (22, 23-26) in response to said multipath signal.

6 more elements

Dependencies are inferred from the claim text.