Jackson Labs RSR GNSS Transcoder, Руководство пользователя

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© 2017 Jackson Labs Technologies, Inc. 3
RSR GNSS Transcoder™ User Manual
integrated Chip Scale Atomic Clock (CSAC) for ultimate frequency and phase stability and holdover
performance.
The RSR GNSS Transcoder™ can accept PVT fixes over the RS-232 or USB serial ports via its
built-in NMEA parsing as well as using standard SCPI commands. Simulation motion control
commands can be stored in internal EEPROM and these commands can be used to automatically start
a dynamic simulation scenario with full autonomy from any external control requirements. Front-end
GNSS receivers can be connected via the RS-232 serial port with auto-detection and
auto-configuration of uBlox and Rockwell Collins GPS receivers such as the MicroGRAM, RSR
Puck, GB-GRAM, with uBlox gen. 5, 6, 7, and 8 GNSS receiver product lines also being supported.
The RSR GNSS Transcoder™ includes a complete Jackson Labs Technologies, Inc. CSAC GPSDO
module which allows automatic disciplining of either the internal high-stability TCXO, or the
optional internal CSAC oscillator to an external 1PPS reference using battle-proven JLT disciplining
algorithms. The RSR GNSS Transcoder™ also has outputs for CMOS 10MHz and 1PPS signals as
generated by the internal CSAC and/or TCXO. The RSR GNSS Transcoder™ is compatible to the
GPSCon control and monitoring program available for free on the Jackson Labs Technologies, Inc.
website.
1.2 Operating Principles
The RSR GNSS Transcoder™ is based on a next generation, fully integrated, full-constellation GPS
simulator. The unit includes an ARM Cortex main processor that handles communications,
calculations, and oscillator disciplining, and a high-integration FPGA that includes hardware RF
signal generators for each GPS channel. Tight coupling between the processor, the FPGA, and the
timing reference allows real-time encoding of PVT/PNT data into a GPS L1 C/A code RF signal.
Baseband IF signals in IQ format from each GPS channel go through an adder tree, and are then RF
modulated using a TX DAC to the GPS L1 frequency of 1575.42MHz. This is done by using Nyquist
harmonics of the DAC sample frequency to avoid having to generate an RF carrier signal or
high-power RF artifacts at L1 frequency which are extremely hard to mitigate and to shield due to the
extremely low power levels of GPS L1 signals (below -120dBm typically). The RF Nyquist
harmonic is then wave-shaped, filtered, and further attenuated. A splitter feeds an on-board 8th
generation GNSS receiver which provides signal monitoring and calibration capabilities. The signal
is final-filtered, and passed out of a resistive pad that includes a 186 Ohms DC resistance to ground
to simulate a typical GPS antenna load to the GNSS DUT receiver. The RSR GNSS Transcoder™ RF
output is compatible with external GPS-provided antenna voltages up to 6V.
The RSR GNSS Transcoder™ includes circuitry to time-stamp an external 1PPS reference signal to
better than +/-2.8ns typically as well as disciplining circuitry for its internal high-stability TCXO or
an optional CSAC oscillator mounted onto the board. It also includes a regulated 5.4V power supply
circuit to provide power to an external GNSS receiver. Additional features include a USB port, a
9-DOF INS, and a user-controllable RF output power level.
1.3 General Safety Precautions
The following general safety precautions must be observed during all phases of operation of this
instrument. Failure to comply with these precautions or with specific warnings elsewhere in this
manual violates safety standards of design manufacture, and intended use of the instrument. Jackson