Abstract: A sample-and-hold type phase detector provides a linear positive or negative going ramp signal that may be used to linearly control a phase-locked loop over approximately a .+-.360.degree. phase range.

Abstract: FM receivers for communications at UHF frequencies often use automatic frequency control (AFS) or phase lock to precisely control a local oscillator. By causing the local oscillator to track errors and slow variations in the frequency of the received signal, these control loops suppress DC and low-frequency modulation components in the intermediate frequency signal and interfere with demodulation of low frequency information, such as digital signalling data. This invention permits recovery of the full modulation spectrum with flat frequency response. A conventional FM demodulator recovers the high frequency modulation components; the frequency control signal for the local oscillator provides the low frequency components. Combining the components with proper weighting produces recovered modulation with bandwidth limited only by the IF bandpass filter of demodulator.

Abstract: A capacitor bias unit includes a first path (26) having a first impedance (29) and a second path (27) having a low impedance and a switch (31) connected between a voltage reference source and a capacitor (23). The capacitor can either be subjected to normal charge characterisitics or quick charge by closing the switch (31). Maintaining an appropriately charged state on the capacitor (23) aids in preventing netting error voltage steps from introducing DC component signals that adversely effect proper decoding and reception of demodulated data.

Abstract: An improved frequency modulator apparatus for use in phase-locked loop (PLL) frequency synthesizers is disclosed which makes possible high deviation, low distortion, FM signals for a wide range of modulating signals, such as digital data or low frequency tone modulation. In a first embodiment having the improved frequency modulator, this apparatus advantageously injects the modulation signal into two ports, one at the VCO and the other provided in an unmodulated reference source signal chain. By properly balancing the levels into each of these two ports, a cancellation effect occurs which nulls the modulation signal at the output of the phase detector. In a second embodiment, the improved frequency modulator is incorporated in a PLL frequency synthesizer with an offset mixer to achieve relatively wide percentage deviation at a low frequency RF carrier.

Abstract: A modulation and range shift device for use with a PLL frequency synthesizer VCO. The modulation signal is provided to the negative side of the tuning varactor (16) of the VCO (14). In addition, variable voltages can be applied to the negative side of the tuning varactor (16) to achieve range shift as desired. Component variations in the modulation section (18) need not be varied to accommodate changes in the loop filter (12 and 13) of the PLL circuit.

Abstract: A programmable frequency synthesizer is disclosed having most components implemented on a single large scale integration (LSI) chip, which facilitates rapid frequency acquisition. Provision is made by the present invention to configure the frequency synthesizer for use in either a receiver or a transmitter. In the transmitter mode, modulation cancelling allows modulation down to approximate DC. A serial programming protocol is provided to program the frequency synthesizer.

Abstract: A receiver for frequency modulated signals, having down-conversion to a baseband, zero intermediate frequency for selectivity, followed by up-conversion to a non-zero IF for amplification, limiting, and demodulation.A phase-lock loop locks the frequency of the down-conversion source to the center frequency of the signal coupled to the baseband IF, converting the signal to precisely zero frequency. This avoids the beat note often found in direct conversion systems. The phase-lock loop additionally provides inherent demodulation of the FM signal.The received FM signal is coupled to the baseband IF through a radio frequency amplifier for improved sensitivity and local oscillator isolation, or through a first IF comprising a mixer, local oscillator, filter, and amplifier.

Abstract: A null initiated priority channel monitoring system provides enhanced nonpriority signal intelligibility and/or enhanced priority channel sensitivity during sample times. The priority channel or channels are monitored during nulls in the received nonpriority signal. The system can have a minimum time period between priority channel monitoring periods to avoid substantially continuous priority channel monitoring. The system can also have a maximum time period between priority channel monitoring or sampling periods to avoid missing any priority channel signal.

Abstract: A null initiated priority channel monitoring system provides enhanced nonpriority signal intelligibility and/or enhanced priority channel sensitivity during sample times. The priority channel or channels are monitored during nulls in the received nonpriority signal. The system can have a minimum time period between priority channel monitoring periods to avoid substantially continuous priority channel monitoring. The system can also have a maximum time period between priority channel monitoring or sampling periods to avoid missing any priority channel signal.