Jackson Labs Micro-JLT GNSS, Руководство пользователя

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Micro-JLT GNSS™ User Manual
2.4 Connecting the GNSS Antenna
Connect the GNSS antenna to the SMA connector J2. Caution: use a Lightning Arrestor on your
Antenna setup. Use an amplified GNSS antenna that is 3.3V LNA compatible. The Micro-JLT
GNSS™ GNSDO GNSS receiver is a 72 channel high-sensitivity multi-GNSS receiver with very
fast lock time.
The Micro-JLT GNSS™ unit is factory set to use Position Hold mode, and will initiate an Auto
Survey process after power-on to establish its new position. The Auto Survey process may last
up to 3 hours. The units’ antenna should not be moved when set to Position Hold mode. Please
set the unit to 3D mobile mode using the GPS:TMODe OFF command in Section
3.3.25 when
the unit is to be used in a mobile environment where the antenna position can change more
than 1 foot during operation.
The Micro-JLT GNSS™ is capable of generating standard navigation messages (see GPS:GPGGA,
GPS:GPZDA, GPS:GPGSV, GPS:PASHR, and GPS:GPRMC RS-422/TTL serial commands) that
are compatible with most GPS-based navigation software.
The GNSS receiver generates a 1PPS time signal that is phase synchronized to UTC(USNO). This
1PPS signal is used to frequency-lock the 10MHz output of the Micro-JLT GNSS™ GNSDO to
UTC, thus disciplining the unit’s 10MHz frequency output to the US Naval master clock for very
high frequency accuracy (typically better than 10 digits of frequency accuracy when locked to GNSS
signals).
2.5 Remote serial control
The unit is controlled via the RS-422/TTL serial port at 115200 baud, 8N1. Other baud rates can be
set via the SCPI command found in Section
3.9.3 .
Attach the Micro-JLT GNSS™ unit to your PC’s terminal program, the cost-free Jackson Labs
GPSCon software package available on the JLT website support page (see
Chapter 5 ), or a
third-party freeware Windows-based application program called Z38xx also available on the JLT
website support page. The GPSCon and Z38xx programs can be used to control and track the
performance of the Micro-JLT GNSS™.
2.6 Loop parameter adjustment
All loop parameters can be controlled via the RS-422/TTL serial port.
Loop parameters are optimized for the OCXO on the board, and changing the factory settings may
result in the unit’s performance to deteriorate. By default the settings are optimized for quick
frequency error correction and slow phase offset error correction, favoring the highest possible
frequency accuracy and ADEV performance over fast phase error corrections.
The commands to control the loop parameters are part of the servo? command. See also the
SERVO
Subsystem section below.
The individual commands are:
EFC Scale: this is the proportional gain of the PID loop. Higher values will give quicker
convergence, and faster locking of the GPS time (lower loop time constant), lower values give less
noise. Values between 0.7 (good double oven OCXO) and 6.0 (simple single-oven OCXO) are
typical.