Abstract: A data communication receiver (10) uses a decision feedback demodulator (32) to remove data from a received signal. Quadrature components of the received signal define a received phase. The received phase is rotated (46) by an amount predicted to compensate for phase and frequency errors. After this rotation, a decision circuit (52) determines the modulation phase for a current symbol. A phase rotator (64) compares the modulation phase with the received phase to generate a measured phase error for the symbol. This measured phase error and measured phase errors from past symbols are averaged in a combination circuit (80) to produce a phase estimate. The past measured phase errors are also processed to determine the amount of change in measured phase error that has occurred over a number of symbols. This processing yields a frequency estimate. A phase rotator (94) merges the frequency and phase estimates for use in compensating a current received phase.

Abstract: A bit error estimator produces a count of detected errors in a TDMA burst data radio transmission. An input phase signal is translated into one of a number of quadrants. A feedback phase estimator then averages the difference between the input phase signal and an output phase signal in a feedback loop to determine an average of the signal differences. The bit error rate estimator then produces a pseudo error count over a predefined time period which is proportional to the number and magnitude of any bit errors in the TDMA burst data radio transmission.

Abstract: A digital single sideband modulator (10) includes a relatively complex CMOS NCO (14) that drives a relatively simple ECL frequency translator (30). The frequency translator (30) outputs a digital signal that is converted to analog by a D/A (44) and then filtered in a bandpass filter (46) having a pass band including a frequency of twice the NCO's clock frequency. The NCO (14) generates a modulated intermediate frequency NCO signal having quadrature components. The frequency translator (30) multiplies real and imaginary components of the NCO signal by real and imaginary components of digitized SIN, COS sampling functions (48, 50). The resulting products are added together. The adding operation is performed by a multiplexer (32), whose selection input is driven at twice the carrier frequency, and the multiplying operations are performed by a selective negation circuit (34), that is driven at the carrier frequency.

Abstract: A transponder demodulates a phase modulated ranging signal transmitted by an earth station. The transponder converts the analog ranging signal to digital form. The digital ranging signal is demodulated into its I and Q phase components. Next the demodulated ranging signal is re-modulated and digitally combined with a selected transmit frequency. Then the re-modulated ranging signal is converted from digital to analog form. The ranging signal is transmitted to the earth station.

Abstract: A method and apparatus for generating two phase-coherent first and second signals with arbitrary frequency ratio includes programming a first numerically controlled oscillator (NCO) with a first frequency word to produce a first NCO output. The first NCO output is processed to produce the first signal. The first frequency word is multiplied in a multiplier to produce a second frequency word which is corrected in phase relative to the first frequency word. A second NCO is programmed with the corrected second frequency word to produce a second NCO output. The second NCO output is processed to produce the second signal.

Abstract: A method for multiplexing a series of frequency division multiple access (FDMA) signals includes providing complex channels offset relative to the FDMA signals. Each FDMA signal is filtered to be centered and occupy one-half of the bandwidth of each complex channel, leaving an "off" channel between each pair of successive FDMA signals. The real part of the multiplexed output signal is processed and higher frequency signals of FDMA signals image into the "off" channels. Demultiplexing includes aligning a demultiplexing channelization pattern with the multiplexed input signal contained in input channels. The input channels are one-half a bandwidth of each of the complex channels. The input channels contain a sequence of FDMA signals separated by a reverse sequence of images of the FDMA signals. Consecutive even-numbered input channels correspond to consecutive complex channels of the complex channels and the sequence of FDMA signals can be extracted from the complex channels.

Abstract: A coherent transponder having a transmitter and a receiver operating at different frequencies with each including a numerically controlled oscillator for controlling the frequency thereof through a single-sideband modulator and various outputs from a phase-locked loop the frequencies of the numerically controlled oscillators and the phase-locked loop being referenced to a single crystal controlled oscillator.

Abstract: In a delay-lock one-delta (.+-.1/2 chip) dithered PN code tracking loop, an indication of lock in the PN code tracking loop is provided by delaying the dithered local PN code by a half chip to produce a +0, -1 dithered PN code that is then multiplied with the received PN-spread IF signal to produce a signal proportional to the correlation of this dithered code offset from the received code. The correlation signal is bandpass filtered, amplified with AGC control, and square-law detected to obtain a DC signal proportional to the degree of correlation. The DC signal is multiplied by the dithering control signal to effectively subtract noise voltage from the lock correlation signal which is then compared with a PN lock status signal.

Abstract: An automatic gain control (hereinafter referred to as AGC) circuitry is used in conjunction with a Costas loop detector to provide positive gain control during the acquisition and tracking modes of the operation of a receiver. The circuitry includes circuitry for deriving a noise estimate signal from one channel of the Costas loop and circuitry for subtracting the noise estimate signal from the data and noise signal combination in the other channel of the Costas loop for providing the automatic gain control signal to prevent false locking.