Abstract: An automatic IF amplifier band width switching circuit is provided in which band width is switched from broad to narrow in response to either high frequency noise or a predetermined magnitude of interference voltage when the FM detection output is at zero volts. The switching signal may be combined with a hum signal from the tuning knob so that only switching in one direction is possible after tuning is complete.

Abstract: A microprocessor controlled radio receiver system for switching bandwidths of an intermediate frequency stage from a normally scanning mode using a relatively narrow bandwidth to a second mode using a relatively wide bandwidth automatically when there are no interfering signals from adjacent channels of a channel or station selected for receiving. Upon selection of a channel for listening the microprocessor controlled synthesizer causes the synthesizer to scan up one adjacent channel and down one adjacent channel to determine if there is an interfering signal therefrom and then returns to the selected channel. In the event of no interfering signal from an adjacent channel, switching is effected in the IF stage from a narrow bandwidth to a wide bandwidth to improve the quality of reception. If there is an adjacent channel signal detected of sufficient IF energy next to the selected channel, then the narrow bandwidth mode used during the scan will be maintained.

Abstract: 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 the FM carrier level, converts the rate at which these noise peak events occur into a control voltage whose average magnitude controls the bandwidth of a filter inversely to the noise peak event rate. When this method is applied to FM receivers with threshold extending FM feedback loops, the control voltage also increases the loop feedback factor thereby reducing distortion and better optimizing the distortion-threshold trade-off.

Abstract: A Modem utilizing process technology compatible CCD and IGFET circuits and sub-systems incorporated on a single I.C. chip. CCD transversal filters are employed as bandpass filters, being tuned for different modes of operation by adjustment of the clock frequency. The bandpass filters are operated in conjunction with a charge amplifier to remove d.c. offset from the analog output of the filters. The demodulator section of the Modem also incorporates low-pass filter employing switched resistors. The modulator section includes waveform generators based on a digital-to-analog converter including switched capacitors having values selected such that a sine wave having minimal distortion is generated when switched in proper sequence. Provision is made for digital inputs to control the frequency and amplitude of the sine wave output. The Modem can be operated under control of a microprocessor.

Abstract: An FM receiver including a noise suppressing circuit in which the signal from which the noise is detected is taken from a front-end section of the receiver and a correction to the noise is made prior to the detector of the receiver. The noise is suppressed by terminating the received signal upon detection of the presence of noise and holding the level which was present before the noise was detected for a predetermined period of time. By detecting the noise in a signal from the front end of the receiver and by making the correction prior to the detector circuit, only a very short predetermined time period need be used and no complicated pilot signal processing circuit is required.

Abstract: In a communication receiver, a first mixing circuit, a first band-pass filter responsive to the output of the first mixing circuit, a second mixing circuit responsive to the output of the first band-pass filter, a second band-pass filter with a different center frequency from that of the first band-pass filter responsive to the output of the second mixing circuit, a first local oscillator, the output of which is applied to the first mixing circuit and a second local oscillator, the output of which is applied to the second mixing circuit. Various kinds of interference signals are eliminated by changing the output frequencies of the first and second local oscillators to thereby vary the effective bandwidth and center frequency of the signals which can pass through the receiver and thus eliminate interference. In addition, a third mixing circuit is responsive to the output of the second band-pass filter.

Abstract: A system which provides frequency conversion and continuously variable bandwidth control uses fixed filters to which opposite edges of the passband of the signal are applied in inverted frequency relationship. A channel contains the filters and three mixers to which injection signals derived from a single variable frequency oscillator and a fixed oscillator are applied to vary the bandwidth of the system without affecting the center frequency of the signal after processing in the system. The system may be designed to obtain either a variable bandpass or rejection band filtering characteristic.

Abstract: In a communication system, a signal detection and acquisition system, which is capable of locating and phase-locking onto a narrow-band signal in a large frequency uncertainty region in a short period of time, employs the following series of operations:(a) sequentially search for signal power in adjacent frequency bins into which the frequency uncertainty region is divided,(b) find the widest loop filter bandwidth at which the receiver phase lock loop can lock onto a transmitted signal,(c) sweep the loop carrier reference oscillator and phase lock onto the transmitted signal,(d) convert the bandwidth of the loop filter at which phase lock was acquired to the bit rate bandwidth, and(e) bit synchronize and begin data recovery.

Abstract: An integrated circuit, when operated from a simple single-pole-double throw switch, performs all of the functions required to switch modes in an FM-AM radio. The radio frequency circuits are switched directly and, in response to the AM oscillator circuit state, electronic switching is employed to switch the FM limiter, AM mixer, and audio amplifier. In the FM mode, the audio amplifier has high fidelity wide band response. In the AM mode, the audio amplifier is switched to operate with a reduced bandwidth. Thus, the audio amplifier does not produce signal components that can be picked up by the AM antenna, where they are interpreted as noise.

Abstract: In a superheterodyne radio receiver, by observing the RF and IF signal levels is detected an occurrence of an interference caused by an interfering strong signal of an adjacent station at a frequency close to that of a desired station signal to be received by the receiver. In case such interference is detected, a cancelling signal is fed to the RF amplifier stage to cancel out this interfering station signal, or the selectivity of the RF amplifier stage is set to be sharper in order to reject the interfering station signal.

Abstract: Circuitry for detecting the spectral distribution of a signal that is phase indicative of a digital logic level and providing feedback signals for use in adjusting the signal amplitude of the spectrum to have a substantially zero slope over the relevant frequency bandwith. The correction is obtained by applying voltages to variable impedance pin diodes forming part of a tuned filter circuit.