Abstract: A tau-dither code correlation tracker includes a code clock and phase shifter for clocking the local code. A sequence of tau-dither patterns are applied to the phase shifter wherein each pattern has an incrementally displaced average phase shift with respect to an adjacent pattern in the sequence. The incremental average phase shift displacements are smaller than the phase shift increments provided by the code clock for enhanced resolution. The correlator output is amplitude detected and applied directly and through a plurality inverter to an electronic switch. The electronic switch is controlled to switchably apply the direct and polarity inverted amplitude signal to an integrator in accordance with the tau-dither pattern. The integrator output is compared to a threshold to control the sequence of tau-dither patterns.

Abstract: A phase differential determining apparatus generates low frequency output signals from a multiple channel receiver and extracts relative phase angles of the received RF signals therefrom. The same local oscillator signals, which are phase locked to one of the received RF signals, are utilized for all channels thus preserving the phase difference of the RF signals during the heterodyning process so that phase angle differences between the low frequency output signals is the same as the phase angle differences between the received RF signals. The relative phase angles are determined at the low frequency output level by phase shifting a low frequency signals from the local oscillator that is phase locked to a reference channel and varying the phase shift applied thereto until the phase difference between this low frequency local oscillator signal and the low frequency output signal of the selected channel is zero.

Abstract: In a Global Positioning System type of navigation system, a biphase modulated radio frequency input signal is applied to the "front end" of a double heterodyne receiver having a second intermediate frequency stage which operates in the audio frequency range. The audio output signal is phase locked to a 1 KHz reference signal and is applied to a microprocessor for processing via an interface circuit which includes a relatively simple amplitude detector and a novel biphase detector. The microprocessor also controls the phase shifting of a pseudorandom noise code generator whose output is modulated with the output of the first intermediate frequency stage of the receiver.

Abstract: A receiver accurately measures the Doppler shift of a radio signal from a transmitter having a known frequency and moving with respect to the receiver by using the signal from another transmitter of known frequency as a reference. The signals from the two transmitters are received by a single antenna, separated, and processed in separate channels. In a typical application using Global Positioning System satellite signals, each signal is discretely extracted by auto-correlation with its own pseudorandum noise signal, filtered, amplified, and applied to second mixers in phase locked loops in the respective channels. The two resulting second IF signals are applied to an output mixer whereupon the resulting difference output signal represents the difference in frequency between the two Doppler signals.

Abstract: The binary state of each cycle of a biphase modulated input signal is detected by a "D" flip-flop when it is clocked by a locally-generated reference signal. When the binary state of the input signal has a first value at clocking, the reference signal is passed through a first exclusive OR gate unchanged. When the binary state of the input signal has the opposite value, the reference signal is inverted by the same OR gate. The output of the first OR gate and the input signal are applied to a second exclusive OR gate to provide a pulse train having a duty cycle indicative of the phase error between the input signal and the reference signal. The latter pulse train is filtered and used to adjust the phase of the reference oscillator until the phase error is eliminated and the circuit is in balance. The binary state of the flip-flop is indicative of the binary state of the input signal.

Abstract: Symbology is written on a radar plan position indicator display with a rotating beam deflection field. The PPI radar range is quantized into range increments and digital data representative of the symbology to be written are inserted into a shift register which is clocked in synchronism with the range sweeps to provide interleaved digital data to the video input of the display. The normal radar video data is combined with the symbology data so that the symbology and normal radar returns are simultaneously written in real time. A portion of the symbology generating apparatus provides a manual acquisition marker comprising a range ring and an azimuth geometric figure. A range switch gates a clock pulse signal into a range up/down counter for incrementing and decrementing the number therein, the digital output of the counter being representative of the range of the range ring.