Abstract: A heterodyne receiver has a mixer with at least one transistor whose operating point can be varied dynamically. The quality of the output signal from the mixer is assessed in order to control the operating point. The operating point is set such that the collector current is increased when the intermodulation interference is high, thus improving the intermodulation resistance. The collector current is reduced when the intermodulation interference is low, thus reducing the transistor noise. Furthermore, the current drawn is reduced in this situation. The circuit and the method are particularly suitable for RF receivers without tunable input filters, and for receivers in which the power consumption must be low.

Abstract: A circuit for breaking a signal path has not only a switching means but also a low-pass or bandpass filter whose frequency characteristic is switchable or bypassable. The insulation between the input and the output when the switching means is open, which decreases with frequency in the case of ordinary switching means, is compensated for by the filter which is then connected. In one embodiment of the circuit, an out-of-band signal is applied to the circuit in addition to the useful signal. The out-of-band signal is intended to be supplied permanently to an evaluation circuit, regardless of the switching position of the switching means. To this end, the out-of-band signal is tapped off downstream of the filter, and the filter is designed such that the out-of-band signal can pass through the filter. In the case of a circuit for selecting one of two inputs, at least one of the inputs is provided with a switchable or bypassable filter, and the switching means is a selection means.

Abstract: In a circuit for reception of signals which have been modulated onto electromagnetic waves, an antenna arrangement (11) having a variable resonant frequency, a tunable oscillator, a variable gain amplifier, an evaluation circuit (14) and a decoder (13) are provided. The evaluation circuit (14) is supplied with the control signals of the oscillator (VT) and of the amplifier (VAGC) and with an error rate signal (BER) from the decoder (13). The resonant frequency of the antenna arrangement (11) is varied as a function of the signals which are applied to the evaluation circuit (14), such that the resonant frequency of the antenna arrangement (11) is matched to the respective reception conditions. This makes it possible to compensate for changes in the reception conditions, such as those which are caused, for example, by people or objects in the vicinity of the antenna arrangement (11).

Abstract: A circuit for breaking a signal path has not only a switching means but also a low-pass or bandpass filter whose frequency characteristic is switchable or bypassable. The insulation between the input and the output when the switching means is open, which decreases with frequency in the case of ordinary switching means, is compensated for by the filter which is then connected. In one embodiment of the circuit, an out-of-band signal is applied to the circuit in addition to the useful signal. The out-of-band signal is intended to be supplied permanently to an evaluation circuit, regardless of the switching position of the switching means. To this end, the out-of-band signal is tapped off downstream of the filter, and the filter is designed such that the out-of-band signal can pass through the filter In the case of a circuit for selecting one of two inputs, at least one of the inputs is provided with switchable or bypassable filter, and the switching means is a selection means.

Abstract: A heterodyne receiver has a mixer with at least one transistor whose operating point can be varied dynamically. The quality of the output signal from the mixer is assessed in order to control the operating point. The operating point is set such that the collector current is increased when the intermodulation interference is high, thus improving the intermodulation resistance. The collector current is reduced when the intermodulation interference is low, thus reducing the transistor noise. Furthermore, the current drawn is reduced in this situation. The circuit and the method are particularly suitable for RF receivers without tunable input filters, and for receivers in which the power consumption must be low.

Abstract: Whenever the oscillator frequency is a fraction or a multiple of the received frequency, another received frequency could in turn be there, which would then work as a kind of received disturbance frequency, and thus oscillator pulling occurs, which then severely impairs evaluation of the received signal. The method according to the invention for driving a receiver stage having a selection means, having a control unit and an oscillator is distinguished by the fact that the selection means is driven such that whenever the oscillator frequency is a fraction or a multiple of a received disturbance frequency, this received disturbance frequency is attenuated by the selection means.

Abstract: In a circuit for reception of signals which have been modulated onto electromagnetic waves, an antenna arrangement (11) having a variable resonant frequency, a tunable oscillator, a variable gain amplifier, an evaluation circuit (14) and a decoder (13) are provided. The evaluation circuit (14) is supplied with the control signals of the oscillator (VT) and of the amplifier (VAGC) and with an error rate signal (BER) from the decoder (13). The resonant frequency of the antenna arrangement (11) is varied as a function of the signals which are applied to the evaluation circuit (14), such that the resonant frequency of the antenna arrangement (11) is matched to the respective reception conditions. This makes it possible to compensate for changes in the reception conditions, such as those which are caused, for example, by people or objects in the vicinity of the antenna arrangement (11).

Abstract: Whenever the oscillator frequency is a fraction or a multiple of the received frequency, another received frequency could in turn be there, which would then work as a kind of received disturbance frequency, and thus oscillator pulling occurs, which then severely impairs evaluation of the received signal. The method according to the invention for driving a receiver stage having a selection means, having a control unit and an oscillator is distinguished by the fact that the selection means is driven such that whenever the oscillator frequency is a fraction or a multiple of a received disturbance frequency, this received disturbance frequency is attenuated by the selection means.

Abstract: Whenever the oscillator frequency is a fraction or a multiple of the received frequency, another received frequency could in turn be there, which would then work as a kind of received disturbance frequency, and thus oscillator pulling occurs, which then severely impairs evaluation of the received signal. The method according to the invention for driving a receiver stage having a selection means, having a control unit and an oscillator is distinguished by the fact that the selection means is driven such that whenever the oscillator frequency is a fraction or a multiple of a received disturbance frequency, this received disturbance frequency is attenuated by the selection means.

Abstract: Components for analog or digital input signals are in each case connected by switchable means to a controllable oscillator. The switch condition of the switchable means is set automatically and/or manually as a function of the input signal.

Abstract: A filter circuit having an amplifier stage, an upstream filter and a downstream bandpass filter. The filter includes, inter alia, a rejection circuit tuned to an intermediate frequency and a series circuit, tuned to an image frequency and formed by a capacitor and a .lambda./4 coaxial stub. The inductance formed by the coaxial stub is shared by the series circuit and the rejection circuit.