Abstract: A phase modulation system includes a phase mapping circuit (218) for mapping binary data into a plurality of discrete phase values in accordance with a predetermined phase modulation scheme. The discrete phase values are then filtered in the phase domain by a filter (220) to provide a filtered output. This filtered output is then digitized and input to a numerically controlled oscillator for phase modulating a carrier.

Abstract: A seismic telemetry system with automatic power leveling is comprised of a command station (10) and a plurality of remote data acquisition units (14). Each of the DAU's (14) includes an antenna (18) for receiving commands and transmitting data and is connected to a T/R switch (34). Commands are received by command receiver (48) and entered into a system control (50). A power detect circuit (52) is provided for measuring signal strength of the received carrier and this information is compared to an internal reference in the system control (50) and the power output level of the transmitter (56) is adjusted. A transmit power detect circuit (60) is provided for measuring the actual power output by the transmitter (56). This measured power level is compared in the system control (50) with the internal references to determine if the actual power output is equal to the expected power output. If not, an offset is provided to adjust for any discrepancies.

Abstract: A symbol generator is provided for generating a filtered analog waveform for use in phase modulating a carrier. A memory (30) is provided for storing predetermined waveform segments. The waveform segments are correlated with an input data stream. The data stream is converted to an address for the memory (30) to output a digital value to a D/A converter (122). The output of the D/A converter (122) is comprised of in-phase and quadrature-phase components which are input to a sample and hold circuit for generating the analog signals. The waveform segments are then sequentially assembled and input to a vector modulator (168).

Abstract: A real time seismic telemetry system includes a central station (10) for communication with a plurality of remote data acquistion units (14). The command station (10) has a command unit (34) for controlling the operation of a transmitter (40) for providing instructions to the data acquistion units (14). The data acquistion units (14) receive the data on a receiver (80) and process the data in a logic control circuit (88). Remote data is picked up with a hydrophone (30) and converted to digital data for transmission through a transmitter (78) which is tuned to a discrete channel for each data acquistion unit (14). The command station (10) has a PCM receiver (62) tuned to each of the channels for demodulating the data stream therefrom. A digital receiver (66) is provided for synchronizing and processing the data. The digital receiver (66) synchronizes both to the bit rate and to the beginning and ending of the digital word such that data contained in the digital word can be multiplexed onto a data bus (68).