Abstract: A digital radio receiver is described. The digital receiver of the present invention contemplates a digital radio receiver which operates on a received analog signal which has been converted to a digital form after preselection at the output of the antenna. The digital receiver of the present invention comprises a preselector, a high-speed analog-to-digital (A/D) converter, a digitally implemented intermediate-frequency (IF) selectivity section having an output signal at substantially baseband frequencies, and digital signal processor (DSP) circuit performing demodulation and audio filtering. The radio architecture of the present invention is programmably adaptable to virtually every known modulation scheme and is particularly suitable for implementation on integrated circuits.

Abstract: A digital receiver for GPS C/A-code signals is described. The GPS receiver of the present invention provides reception and tracking a plurality of satellites simultaneously, using four separate receiver channels. The GPS receiver of the present invention includes an analog front-end for selecting and frequency translating the received GPS signal. The GPS receiver further includes a highspeed digital signal processor for recovering the despread data of the GPS signal. The baseband signal is further processed by a general purpose digital signal processor for signal search, tracking, and data recovery operations, and a microprocessor provides overall receiver control, and interface with the operator of the GPS receiver.

Abstract: An apparatus and method for determining the period and frequency of a signal intefering with a desired Loran C signal are provided. A sample of the interfering signal is generated at a time corresponding to the peak of the autocorrelation function of the interfering signal with respect to the predetermined pulse tracking reference point of the Loran C signal. Indicia of the period and frequency of the interferer is obtained from the timing of the sample generated at the autocorrelation function peak.

Abstract: A method and apparatus for attenuating an interfering signal corrupting a desired Loran C signal is provided. An interfering signal sample is determined which occurs at the peak of the autocorrelation function of the interfering signal such that the period of the interferer is known. The sample occurring at the peak of the autocorrelation function is added to or subtracted from the desired Loran C signal sample taken at a predetermined reference point during the pulses thereof such that the interfering signal is cancelled or substantially attenuated.

Abstract: An interference rejection apparatus is provided which samples the Loran C signal at selected pulse tracking reference points. The Loran C samples are separated into even and odd groups by appropriate summing-weighting circuitry. The even pulse and odd pulse waveforms thus produced are analyzed to determine the presence of an interfering signal which corrupts either of the off or even pulse groups. Upon detection of interference with either the even or odd Loran C samples, strobe dropping is employed to reject the affected group of samples.

Abstract: Loran C signal processing apparatus is provided which employs a single signal channel or path to process and sample Loran C RF signals and envelope derived Loran C RF signals which in conventional approaches are processed and sampled in separate signal paths.

Abstract: The presence of a pulsed radio frequency signal is detected by periodically sampling such signal with first and second sampling strobes in quadrature relationship. The first and second strobes are separately accumulated for a first period of time overlapping a second period of time during which the first and second strobes are also accumulated. The four sums resulting from such accumulations are compared with a predetermined threshold level to determine the presence of the pulsed radio frequency signal.