Abstract: In order to enhance an RF-AGC sensitivity when a station which may cause mutual modulation disturbance is detected, an automatic memory mode is executed so that data on the six stations with first to sixth highest field intensity are preset in a memory. When a receiver intends to receive an object station among the six preset stations, the differences in frequency between the object station and other preset stations are obtained, and whether or not the object station and each of the other stations retain such frequency relationship that may cause mutual modulation disturbance is detected, based on the frequency difference. With an expectation of mutual modulation disturbance, the RF-AGC is set to have higher sensitivity, while, without such expectation, it is set to have lower sensitivity.

Abstract: A circuit arrangement that reduces selected intermodulation. The circuit arrangement includes a signal amplifier coupled to a bandpass filter via an electrical path. Signal energy outside the passband is reflected back into the amplifier and causes intermodulation. The electrical path is constructed with a length that reduces intermodulation, where the length is an odd multiple of one-fourth the wavelength of a predetermined frequency in the passband. The length of the electrical path reduces intermodulation because certain signals reflected by the bandpass filter are approximately 180.degree., or an odd multiple thereof, out of phase. Energy of problematic signals that are near the edge of the passband or in the stopband is reduced, such as third order intermodulation product and pairs of signals that produce third order intermodulation products.

Abstract: A wireless receiver includes a variable attenuator, a signal-to-noise ratio (SNR estimator), and a received signal strength indicator (RSSI) level detector. The RSSI level of the received signal is used as a primary criterion on setting the attenuator status. Once the attenuator is set based upon the RSSI readings, an SNR check is made to determine the possible presence of IM. Then, further adjustment on the attenuator status is made according to the SNR check.

Abstract: The apparatus and method for estimation and minimization of the carrier multipath response envelope are disclosed. The reduction of the carrier multipath error signal is achieved by using the weighted or modified tracking or estimation circuits. The Modify and Weight signals are generated by the generator of Modify or Weight signals at five different circuit levels.

Abstract: A mixer for use in a direct conversion receiver includes a compensating differential amplifier which injects equal amplitude opposite phase currents with respect to even order distortion currents. The compensating differential amplifier utilizes an ideal current source. The mixer is an active mixer which utilizes four switching transistors. The even order distortion is introduced by non-linear components which demonstrate strong off-channel signals.

Abstract: A communications receiver such as an integrated zero IF receiver comprises an input for receiving an input signal and a zero IF frequency down conversion circuit coupled said input and constructed to provide quadrature related signals (I,Q) at a substantially zero intermediate frequency. In order to balance the signal paths, at least one capacitance in each of the quadrature related zero IF signal paths of the frequency down conversion circuit comprises at least two integrated capacitors connected in anti-parallel. By fabricating the integrated capacitances in this way the symmetry of the circuit is maintained which enhances significantly the second-order inter-modulation performance.

Abstract: In a single-chip multistandard video modulator arrangement in which audio signals for transmission with video signals are first modulated onto a subcarrier and then combined with the video signals for modulation onto a VHF or UHF main carrier, the modulated subcarrier signals are passed through a high-pass filter before being combined with the video signals in order to reduce the amplitude of any audio frequency components, and the resulting variations in main carrier amplitude, which tend to produce "sound in vision" effects.

Abstract: A communication system is provided for increasing communication range between at least two radio communication devices without increasing the output power of transmitted radio signals from the devices, and without increasing the antenna gain of the received signals. Each radio device includes an oscillator for generating a carrier reference signal, and an SATPS receiver which receives at least one standard timing reference signal from at least one SATPS satellite. The received standard timing reference signal is used to continuously adjust the timing and synchronization of the oscillator to improve the accuracy of the carrier frequency signal. The improved accuracy in the carrier frequency signal may then be used to reduce the bandwidth of the modulated carrier frequency signals generated by the radio device to thereby increase the effective communication range and sensitivity of the device.

Abstract: A pager includes a radio frequency (RF) attenuator which is initially rendered inoperative and which initiates attenuation of an incoming RF signal in response to a control signal. An amplifier is coupled to amplify the output of the attenuator. A signal level monitor (24, 26), coupled to the amplifier, determines if the output of the amplifier exceeds a predetermined level. A demodulator (16) is coupled to reproduce a base band signal from the output of the amplifier. A controller, following the demodulator, attempts to establish bit sync during each of a plurality of conventional and intermittently executed preamble searches. If bit sync is not established in a given preamble search and if the level monitor indicates that the output of the amplifier exceeds the predetermined level, the controller applies the control signal to the attenuator for activating the attenuator.

Abstract: An apparatus or system for data communications that provides crosstalk cancellation is disclosed. The apparatus or system removes crosstalk interference (e.g., NEXT interference) from received signals on a given line by adaptively estimating the crosstalk interference induced by certain other of the lines having interfering transmissions and by canceling the crosstalk interference using the estimated crosstalk interference from the certain other of the lines. The invention is useful for high speed data transmissions where crosstalk interference can be a substantial impediment to proper reception of data. In particular, the invention is useful for VDSL and ADSL data transmissions using multicarrier modulation (e.g., DMT), wherein transmission frames for all lines are synchronized but the duration of the direction of transmission can vary due to differing frames.

Abstract: An antenna cosite analysis system with: interactive displays for i) designing an antenna tower for placement of one or more antennas on the tower, ii) designing wireless communication circuits, and iii) relating the antennas on the tower to the wireless communication circuits; and an RF analysis system for analyzing interference between the wireless communication circuits.

Abstract: A amplifier having distortion compensation is employed as a power amplifier for amplifying a linear modulated signal or a low noise amplifier for amplifying a linear modulated signal. The amplifier having distortion compenssation includes an amplifier circuit for amplifying an input signal; an error detecting circuit for obtaining an error signal between the input signal to and an output signal from the amplifier circuit; a coefficient generating circuit for generating compensation coefficients to compensate distortion components of characteristics of the amplifier circuit, based on the error signal according to an adaptive type algorithm; a first outputting circuit for outputting a generated compensation coefficient corresponding to the input signal; and a multiplying circuit for multiplying the generated compensation coefficient to the input signal and inputting a multiplied coefficient to the amplifier circuit.

Abstract: A waveform reconstruction circuit receives an rf signal from an antenna, digitizes it, and then generates an undistorted reconstructed waveform. The reconstructed waveform can then be conventionally mixed and demodulated to extract useful signal information with enhanced receiver fidelity and sensitivity.

Abstract: A communication system mitigates signal distortion of output signals transmitted by a transmitter element (406). The communication system obtains parameters related to, inter alia, the number of traffic channels utilized by the system, the number of RF channels utilized by the system, the voltage levels of certain signal waveforms (321) within the system and information related to power levels being transmitted by the transmitter element (406). The communication system utilizes the obtained parameters to, in a first embodiment, clip the signal waveform at certain portions that exceed a determined threshold, and, in a second embodiment, automatic gain control the signal waveform during a symbol time period. By clipping or automatically gain controlling the input signal into the transmitting element (406), the distortion of a signal output from the transmitting element (406) is mitigated.

Abstract: Crosspolarized signals of unrelated baud rates transmitted through a communication channel (10) become depolarized due to channel distortions such as rain and antenna imperfections. The resulting interference is canceled in a Modified Adaptive Crosspole Interference Canceler (MAXPIC) receiver (50, 70) by adjustment the timing in the crosspolarization path to compensate for the differential delay. Near equivalent bit error rate (BER) performance is achieved for systems utilizing crosspolarized signals with independent baud rates. In one embodiment, the receiver uses a fractionally spaced finite impulse response (FIR) filter (78) that operates at an integer multiple of the direct channel signal baud rate. In another embodiment, a variable delay (54) is used to time-align the received crosspolarized channel signal with the crosspolarization interference contained in the received direct signal.

Abstract: The performance of a radio receive system such as a trunked or non-trunked land mobile multi-channel receiver site is optimized to maximize coverage area and receiver dynamic range while minimizing the potential for intermodulation distortion. A noise test receiver including a noise receiver and a spectrum analyzer measures ambient noise and strong ambient signals. A computer analyzes the resulting spectral information to determine likely intermodulation distortion products and associated amplitudes. The computer compares the measured noise and intermodulation product results with system characteristics to arrive at an optimum variable attenuator setting that maximizes receiver sensitivity and dynamic range while protecting against intermodulation distortion. In one example, the optimized performance parameters are computed dynamically and used to dynamically control the value of a programmable attenuator, thus yielding maximum system performance under varying conditions.

Abstract: A frequency processing circuit has a suppressing circuit for suppressing a lower sideband wave of an input FM signal whose frequency is modulated, a frequency conversion circuit for converting the frequency of an output of the suppressing circuit, and an emphasizing circuit for emphasizing a lower sideband wave of an output of the frequency conversion circuit. The emphasizing circuit emphasizes a share of the amount of the wave suppressed by the suppressing circuit.

Abstract: A cross polarization interference canceler includes a digital conversion unit for subjecting a demodulated signal of one channel to an analog-to-digital conversion out of two channels which are independently formed, using carriers having the same frequency but having planes of polarization which are mutually orthogonal. An interference canceling unit is provided for canceling interference caused by the other channel of the two channels, with respect to the demodulated signal which is digitally converted by the digital conversion unit. The canceler further includes an integrator for carrying out an integration process with respect to the demodulated signal which is digitally converted by the digital conversion unit so as to provide a negative feedback to the digital conversion unit.

Abstract: A frequency-selective interference signal detecting apparatus and method thereof generates as many tone signals as the number of a frequency-selective interference signals at the transmission side of a transmission system and one tone signal corresponding to an optional frequency at an occupied band frequency of the transmission system, transmits all generated tone signals to a receiving side of the transmission system through the transmission channel selectively, computes an SNR with regard to each tone signal by receiving these tone signals at the receiving side, compares the calculated SNR with a preestablished reference value, detects whether or not each of the frequency-selective interference signals exist, provides the degree of such interference, and makes several frequency-selective interference signals detectable so as to raise transmission efficiency of a data signal in the transmission system.

Abstract: A radio receiver front end is disclosed that processes a multi-carrier signal with a large dynamic range. An illustrative embodiment of the present invention incorporates both feedforward and feedback mechanisms to suppress the amplitude of spurious carrier signals so as to prevent those signals from flooding the dynamic range of the mixer that mixes down the multi-carrier signal.

Abstract: In a television receiver a SAW filter (FSAW) is preceded by a coupling network (CNW). The coupling network (CNW) includes an inductor (LP) between two input terminals of the SAW filter (IS1, IS2). It further includes a series resonance circuit (SRC) coupled to at least one of the input terminals (IS1). In order to reduce signal distortion a resistor (RP) is coupled between the two input terminals (IS1, IS2). Alternatively, a resistor (RS) is coupled in parallel to the series resonance circuit (SRC).

Abstract: A circuit arrangement for recognizing adjacent channel interference in a stereo radio receiver, in which a stereo multiplex signal is present. An adjacent channel interference signal is obtained as a function of a direct voltage portion of the stereo multiplex signal and as a function of the spectral components of the stereo multiplex signal above 60 kHz.

Abstract: A source transmitted signal is cancelled at the receiver associated with the transmitter, so that the desired received signal can be extracted from a composite received signal, the composite received signal consisting of the source signal relayed from the relay station along with the desired received signal from the other user in the pair, plus additive noise. The invention takes advantage of the fact that each of the users knows a priori the exact structure of its source transmitted signal and can estimate the channel characteristics between the relay station and itself.

Abstract: Apparatus and a method for inhibiting spurious responses in the receiver stage of a radio telephone are disclosed. A detector detects the transmission of an RF signal from the transceiver and sends a control signal indicative of such transmission to a linearity controller. The linearity controller is coupled to non-linear devices in the receiver stage of a transceiver and varies the linearity of the non-linear devices in accordance with the control signal. Preferably, the linearity is varied by increasing the bias current or voltage for the non-linear devices when the control signal indicates transmission of an RF signal.

Abstract: In an earth station terminal, a cascaded arrangement of downlink half- and quarter-wave polarizers receives a downlink communication signal and a mono-polarized beacon signal from a communications satellite and separates the communication signal into respective polarization components. A receiver is connected to the cascaded polarizers for detecting the in-phase and orthogonal-phase components of a cross-polarization of the beacon signal with respect to the phase of its copolarization. For cross polarization compensation, first and second polarization offset values of the beacon signal are derived from the angular positions of the polarizers, and subtracted from the beacon's in-phase and orthogonal-phase components, respectively, to produce target values. By controlling the polarizers until their angular positions are respectively equal to the target values, the polarization components of the downlink communication signal assume zero vectors.

Abstract: A frequency modulation receiving apparatus comprises a signal-converting circuit for converting a signal received by an antenna into a signal consisting of wave clusters having various frequencies, first limiting circuit for limiting those of the wave clusters which have frequencies outside a first frequency range, second limiting circuit for limiting those of the wave clusters which have frequencies outside a second frequency range narrower than the first frequency range, shearing circuit for combining and outputting a ratio of a signal output by the first limiting circuit and a signal output by the second limiting circuit, frequency-demodulating circuit for frequency-demodulating a signal output by the selecting circuit, detecting circuit for detecting whether or not an adjacent interfering wave exists in a signal output by the frequency-demodulating circuit, and for outputting a signal indicating whether or not an adjacent interfering wave exists in the signal, and control circuit for delaying a signal out

Abstract: A radio receiver (10) comprises a plurality of stages and means for selectively adjusting the stages (16, 18, and 22), as a function of the received signal strength to reduce intermodulation distortion. In still another aspect of the invention, a receiver determines the signal strength of a received signal and uses this information to selectively control stages of the receiver in order to reduce the receiver's current drain.

Abstract: An apparatus and a method for cancelling distortion in a direct conversion receiver, such distortion created by the mixing of the desired signal with the output signal of an local oscillator. Subsequent to filtering the mixer output signal, the even mode distortion component is extracted, phase shifted, amplified and recombined with the mixed signal in such manner as to suppress even order distortion.

Abstract: An equalizer employed with a receiver for cancelling an interfering signal due to low cross-polarization isolation. The present equalizer provides a simple and inexpensive cross-polarization interference cancellation system. The equalizer uses an error signal generated in an adaptive baseband equalizer to determine the magnitude of an interfering signal and inputs a cancelling signal to the co-polarized channel until power in the error signal derived from the adaptive baseband equalizer is minimized. In the equalizer, the determination of the magnitude of the interfering signal is performed at baseband (after demodulation but prior to data detection) and the cancellation is performed at RF, prior to dispersive microwave elements. The equalizer enhances the capability for transmitting two unique signals in the same frequency allocation on orthogonal polarizations. The equalizer operates even if the modulations and data rates on the two channels are different.

Abstract: FM radio receivers, particularly in moving vehicles, are subject to intermittent adjacent-channel interference. It is known to detect such interference and suppress it by narrowing bandwidth in the Intermediate Frequency (IF) signal path. However, it is desirable to again broaden the bandwidth once the interference has subsided. An improved system, which automatically and dynamically adjusts the bandwidth, employs first and second signal level evaluation circuits (11, 12), a comparison stage (13) which compares their outputs, and a variable-bandwidth filter stage (6, 14) controlled by the comparison stage. The comparison stage is programmed with a set of signal difference threshold values and corresponding filter bandwidth values, and controls the filter stage (6, 14) to adjust the bandwidth to the appropriate value, indicated by which signal difference threshold value has been exceeded. In a preferred embodiment, a second IF filter (15) does "double duty" as part of the variable-bandwidth filter stage.

Abstract: In a radio receiver with an input circuit which can be supplied with received signals, with a mixer for deriving an IF signal, and with an IF filter, the passband range corresponds to a usable signal range of the received signal, the received signals are amplitude-modified with an auxiliary signal for detecting intermodulation, in the course of which sidebands are generated outside of the useful signal range. The amplitudes of at least one sideband generated by modulation with the auxiliary signal and of the received carrier are compared in the IF signal. In case of deviations from a ratio based on the modulation factor during modulation with the auxiliary signal, a signal indicating the presence of intermodulation is derived.

Abstract: On receiving a symbol sequence carried by a first-polarization and a second-polarization signal of two orthogonally polarized signals and in order to cancel a cross polarization interference (XPI) component which leaks from the second-polarization signal into the first-polarization signal, a first decision feedback XPI canceller (43) is supplied with a before processed signal derived from the second-polarization signal and with a decided signal which is produced by a decision circuit (22) and which represents the symbol sequence carried by the second-polarization signal with an intersymbol interference component and another XPI component cancelled from the before processed signal. Another decision feedback XPI canceller (44) is similarly operable.

Abstract: A radio receiver front end having both feedforward and feedback mechanisms to suppress the amplitude of spurious signals so as to prevent those signals from flooding the dynamic range of the mixer of the front end. An illustrative embodiment of the present invention comprises splitting the input signal into a first signal and a second signal, creating a third signal based on the difference of the first signal and a difference signal, mixing down the third signal with a first oscillatory signal, isolating a feedback signal from the mixed down signal, mixing up the feedback signal with a second oscillatory signal and creating the difference signal based on the difference of the second signal and the mixed up signal.

Abstract: A fractionally spaced cross-polarization interference canceller, wherein a compensation signal is generated through an adaptive filter operating in a frequency that is an integer multiple of a transmission data frequency. The cross-polarization interference canceller includes a mechanism for generating an error signal used to control coefficients of the adaptive filter in the integer multiple frequency. The mechanism is realized, for example, by using a waveform generator generating an estimate of a baseband signal in the integer multiple frequency using a plurality of estimates of transmission data and coefficients determined by an impulse response of a transmission path.

Abstract: In the following manner, a receiver that receives quadrature modulated signals may determine desired components of the quadrature modulated signals by minimizing effects of transmitted distortion produced by gain, phase, or gain-phase imbalance. A quadrature modulated signal that includes a desired component, a fading component, and a transmitter distortion component is received by the receiver, wherein the transmitter distortion component includes a conjugate component and an imbalance component. The receiver estimates the fading component, the conjugate component, and the imbalance component and determines the desired component based on these estimates and the quadrature modulated signal.

Abstract: An unwanted portion of a radio frequency signal spectrum appearing on a signal line (12) is adaptively canceled by first sampling the unwanted portion of the spectrum, and thereafter filtering the sample, typically at an intermediate frequency, to reduce signal losses. The first sample is then processed to yield a cancellation signal, having a variable phase. The cancellation signal is then injected into the signal spectrum after which time, the spectrum is again sampled. The second sample is correlated with the cancellation signal and the resultant correlation is employed to adjust the phase of the cancellation signal to maximize the cancellation of the unwanted portion of the spectrum.

Abstract: A signal which results from cross modulation of two or more nearby received waves contained in the output of a high-frequency amplifier or mixer of a radio receiver, for example, a low-frequency signal corresponding to a channel separation frequency is extracted. The gain of the high-frequency amplifier or attenuation of a variable attenuator provided in the preceding stage of the amplifier is controlled in accordance with the level of the low-frequency signal. Alternatively, the gain of the high-frequency amplifier or attenuation of the variable attenuator is controlled in accordance with the level of the low-frequency signal when it is equal to or larger than a predetermined value. This permits normal reception of a desired wave, even if the signal receiving level is high.

Abstract: In a cross polarization interference canceller for use in digital radio communications, a signal processing circuit monitors whether numbers of word sync signals and error pulses obtained in error correction decoding exceed specified values, and outputs reset signal RS1 when an abnormality is detected. A signal level detection circuit outputs reset signal RS2 when it is detected that a level of a different polarization side baseband signal from a demodulator is lower than specified. A logical sum RS3 of reset signals RS1 and RS2 is supplied to a cross polarization interference cancellation device, which may have a transversal filter. When the word is not synchronized or the number of error pulses generated in error correcting decoding exceeds the specified value, the self-polarization side can be protected from unnecessary interference and disturbance and the self-polarization side data can be protected from disturbance even though an abrupt abnormality occurs in different polarization signals.

Abstract: A satellite communications system includes a feed array and reflector receiving antenna coupled to a dual-mode network, for generating two channels, with independent signals representing two beams, one for each channel. Each output channel of the dual-mode network contains redundant information relating to a plurality of information channels. In the absence of an interfering signal or intrusion, the combined signals are amplified and block frequency-converted, then de-multiplexed into separate channels, which are each applied through selection switches to a transmitter multiplexer for retransmission. An alternate signal is tapped from each of the two received signal channels, phase controlled, and combined, to produce a combined signal representing a receive antenna beam with a null controllable in position in response to phase. The combined signal is demultiplexed into separate information channels.

Abstract: In one receiver for phase modulated digital signals, bit packet transmitted with known preamble, of the type foreseeing a maximum likelihood estimation circuit for distortion corrections, it is performed the cancellation of isofrequency interfering signals, having the same frequency of the useful signal and the same modulation type as well.This is obtained making an estimation of amplitude (A), phase (.PHI.) and time synchronism (.tau.) parameters of the interfering signal in correspondence of each bit packet and reconstructing the useful signal with a maximum likelihood estimation process employing these parameters (FIG. 1).

Abstract: The present invention concerns a method and a system for demodulating mutually interfering signals according to a suitable synchronism bond between said signals. With such a system a complete decoupling of the demodulators of said signals is obtained. The system is characterized in that on each polarization there is at least a pair of demodulators, a first pair operate a baseband conversion of both signal H and V using the carrier recovery circuit driven by data of one of the two signals (e.g. V) and a second pair operate still a baseband conversion of both signals H and V but using said carrier recovery circuit now driven by data of the other signal (e.g. H).

Abstract: A radio frequency receiver (300) typically contains electronic devices commonly used in amplifying or mixing circuits (315) which are seldom ideal. The non-ideal characteristics of these devices lead to intermodulation (IM) distortion. A measurement of the amplitude of the received signal (301) is taken both unattenuated (503) and attenuated (507). The difference between the two measurements is compared (511) to predetermined limits (L1, L2 or L3) wherein the received signal (310) is determined to be valid, invalid or unsure. A valid received signal is demodulated in the receiver (300). An invalid signal, confirming the presence of IM distortion, is rejected. The unsure signal may be rejected or demodulated as determined by the receiver designer. This type of signal characterization is particularly useful for cellular radiotelephones (101) attempting to gain access to the system provider (111) in which it is registered.

Abstract: A crosstalk detector for detecting the crosstalk of signals optically read from a recording medium having a plurality of tracks. The read signal levels between adjacent tracks at the positions where crosstalk detecting signals are recorded are compared and used to calculate a quantity of crosstalk of the read signals.

Abstract: The radio receiver of the present invention detects the presence of adjacent channel interference in either the lower adjacent channel or the upper adjacent channel and shifts the received signals to remove the adjacent channel interference from the intermediate frequency passband, but only if the other adjacent channel is clear. A maximum amount of the desired signal is retained so that modulation distortion is low. Frequency limits for shifting of the desired signals prevent undesirable amounts of phase distortion from being introduced into the audio signal.

Abstract: An improved adaptive notch filter for removing undesired cochannel FM interference includes in-phase and quadrature signal processing paths in which the undesired FM signal is translated to zero frequency, i.e. to DC. In each of the in-phase and quadrature phase signal paths, a first multiplier translates the input frequency spectrum in a dynamic manner so that the frequency of the undesired FM signal is always centered on DC. The undesired signal, now at DC, is filtered out by a high pass filter with a sharp rolloff. The output of the high pass filter is remultiplied in a second multiplier to translate the desired FM signal back to the original position in the frequency spectrum. In order to eliminate an unwanted difference frequency remodulation signal at the output of the second multiplier, the quadrature phase signal path performs a parallel operation on the same input signal, but with a quadrature phase (90 degree phase shift) control signal.

Abstract: An FM receiver includes an IF unit followed by an LF unit. The receiver has circuitry for changing the signal transmission characteristic of the IF and/or LF units, including a detector module with detector circuits for detecting values characteristic of receiving or interference states, with the inputs of these detector circuits each being connected with a circuit point of the IF or LF unit carrying the signal to be processed and with the outputs of these detector circuits providing signal characterizing receiving the interference states.

Abstract: In a cross-polarization interference canceller employing a transversal filter, when a tap coefficient of the transversal filter is generated by averaging resultant values of correlation between a residual error component and a data polarity signal of a different polarized wave, a moving average derived by averaging with a sum of most recent given number of bits of correlation results, is employed. Even when offset is caused on the correlation results due to random characteristics of the received signal, the offset cannot be accumulated to allow derivation of the true tap coefficient since the sum of most recent given number of bits of correlation results is used.

Abstract: Adaptive IIR digital notch filters useful with RF receivers for reducing interference. One or more notch filters automatically tune, to an interferer frequency, via adapting of coefficients in the z-transform. Each notch tunes independently of any other.

Abstract: A receiver apparatus having a mixer circuit, an oscillator circuit and a tuner circuit is provided with a trap circuit, interposed between the tuner circuit and the mixer circuit, for removing disturbing mutual modulation waves generated by receiving two or more RF signals. Further, the mixer circuit employs a double balanced mixer structure to offset two or more disturbing mutual modulation waves.

Abstract: Apparatus for digital switching of FM signals includes multiple functional switching circuits, each having an input for receiving an FM signal at a first frequency and each generating first switching transients in response to the FM signal. The apparatus includes a dummy switching circuit corresponding to each functional switching circuit. The dummy switching circuits generate second switching transients in response to the FM signal. The second switching transients are shifted in phase relative to the first switching transients such that a crosstalk signal resulting from the first and second switching transients has a frequency of twice the first frequency. The apparatus further includes filters for attenuating the crosstalk signal. By shifting the frequency of the crosstalk signal to twice the frequency of the FM signal, the crosstalk signal is easily filtered.