A plurality of parallel branch paths are connected in an intermediate frequency or high frequency amplifying circuit of a radio receiver for the purpose of switching the bandwidth. Between an intermediate point of each branch path and the ground is connected output electrodes of a transistor, and the base electrode of the transistor is selectively connected to a source of control voltage via a transfer switch to render the selected transistor conductive.

The invention relates to a superheterodyne circuit characterized by comprising a first mixer converting a received signal into the first intermediate frequency, a second mixer converting the first intermediate frequency into a second intermediate frequency, and a product detection stage demodulating the second intermediate frequency to an audio frequency, by having a constitution wherein the local oscillation of the first mixer is input from a VCO for which a PLL circuit is used, wherein the loc...

There is provided an AM receiver in which the bandwidth of an intermediate frequency amplifier is continuously varied in accordance with the received field strength. This AM receiver includes a combining circuit for combining a first AM detection output A from a narrow band intermediate frequency amplifier and a second AM detection output B from a wide band intermediate frequency amplifier to produce an AM signal output of A(1-a.sub.M)+a.sub.M B (where, 0.ltoreq.a.sub.M .ltoreq.1). By varying th...

This invention provides a bandwidth switching circuit for an intermediate frequency amplifier stage in an FM receiver that insures clear reception of desired signals by automatically switching the intermediate frequency amplifier stage between the wide and narrow bandwidths according to the radio field conditions. The bandwidth switching circuit includes a detector for detecting beat components due to interference contained in received signals and a change-over switch for switching the bandwidth...

A method is disclosed for optimizing the bandwidth of a radio receiver cale of receiving widely varying input data rates. The method may be utilized with known superheterodyne receivers having certain modifications to allow for the ability to vary the intermediate frequency and the center frequency of the associated bandpass filters over a continuous range of values. The method includes the steps of determining the optimum intermediate frequency bandwidth for a given input data rate, adjusting a...

Communications systems employing frequency modulation have noise threshold levels that practically limit the minimum received signal level. This limit is particularly significant to satellite earth stations. A method that automatically and advantageously trades improved threshold levels for increased distortion by reducing the noise bandwidth of the receiver as the carrier to noise ratio approaches the threshold level is described. This method senses when noise peaks approach, equal or exceed th...

A high frequency apparatus includes an input terminal 21, a high frequency filter 22 to which a signal input into the input terminal 21 is supplied, a mixer 24, one input of which an output signal of the high frequency filter 22 is supplied to and an other input of which an output signal of a local oscillator 23 is supplied to, an intermediate frequency filter 25 to which an output signal of the mixer 24 is supplied, an output terminal 27 to which an output signal of the intermediate frequency f...

The invention relates to a method for the control of the bandpass width in the filtering of an intermediate frequency signal of an audio receiver of a radio reception apparatus. A signal parameter of a user signal of the audio receiver which is received at a reception frequency is determined and taken into account and a signal parameter of at least one neighboring signal which is received at a neighboring frequency which is adjacent to the reception frequency is determined. The bandpass width of...

A heterodyne receiver includes a tuner to select a frequency of a received signal and a converter to change the frequency of the received signal to an intermediate frequency. A single-pole/double throw switch has an input coupled to an output of the converter, a first output connected to a first band-pass filter and a second output connected to an amplifier. A second band-pass filter is coupled to an output of the amplifier, and a demodulator is coupled to an output of the second band-pass filte...

A method for processing a radio signal which may include a narrowband signal or a wideband signal or both, comprises the steps of receiving the radio signal, initially processing the radio signal using a narrowband filter, switching to a wideband filter for further processing of the radio signal, determining if the wideband signal is acquired, and if the wideband signal is not acquired, alternating between narrowband filter processing for a narrowband filter hold time and wideband filter process...