Abstract: In a demodulator for an antipodal data stream, such as a PSK or FSK demodulator, a signal quality measuring circuit having a high dynamic range. Any signal quality parameter can be measured, such as BER and E.sub.b /N.sub.o. The number of zero crossings in a certain error gate is compared with the total scaled number of zero crossings in the sampling interval. These values are translated into a quantitative measure of signal quality by means of a pre-established table of values obtained during calibration of the instrument. The wide dynamic range of the circuit is achieved by using several gates of various widths. The gates are derived from a bit synchronizer; the system functions without the necessity for superimposing upon the data stream any coding information as is common with BER measurement devices of the prior art.

Abstract: In a data link conveying antipodal (two level) data bits, a signal quality measuring circuit using prestored experiential data acquired during a calibration phase. Any signal quality parameter, such as BER and E.sub.b /N.sub.o, can be measured by the circuit. The number of events falling within an error gate is compared with a more universal measure of bit events occurring during the sampling interval. These values are translated into a quantitative measure of signal quality by means of a prestored lookup table. The error gates can be shaped to represent phase deviations, amplitude deviations, or any combination of phase and amplitude deviations. A wide dynamic range can be achieved by using several different gates of various shapes. The gates are derived from a bit synchronizer; the circuit functions without the necessity for superimposing upon the data stream any coding information as is common with BER measurement devices of the prior art.

Abstract: Statistical properties of a signal are used to distinguish between a voice signal and an "on hook" indication on a low bandwidth digital data link. Noise is intentionally added to the voice signal to guarantee a minimum power level, while not disrupting normal demodulation. A digital signal, having a known maximum power level upon demodulation, is used to represent the "on hook" condition. Upon demodulation, the minimum power level of the noise-colored voice signal is greater than the maximum power level of the "on-hook" signal, and the two signals can be distinguished by a power level threshold detector. This apparatus and technique is particularly well-suited to under-sampled, such as CVSD (continuously variable slope delta), data links, which are usually noisy and distorted. It alleviates the need for direct access to the digital link and simplifies the required hardware and retrofit modifications.

Abstract: A bit synchronous switching system is disclosed which has applicability in a space diversity system of digital telecommunications. Two versions of a signal waveform are received at two remote locations from the same signal source. The end user is able always to receive the more intelligible signal by means of instantaneous switching logic. An acquisition and tracking circuit, which can include a delay lock loop, keeps the two signal streams synchronized. One data stream is used as a reference and the time delay of the other is varied so that the time differential between the two streams is tracked out. The system features continuous tracking and does not require any frame synchronization to be superimposed on the data stream.