Micro-JLT GNSS™ User Manual
10 © 2019 Jackson Labs Technologies, Inc.
2.2 Power
The unit is powered from a +5.2V to +6V max. DC source, with +5.5V nominal voltage. The current
is typically less than 0.6A at 5.5V. Connect a clean +5.5V power supply to pins 10 and 12 of J1, and
ground to pin 2 and 9 of J1. The unit may also be optionally ordered with 5.0V +/-10% supply range
for large volume custom orders.
2.3 Concurrent-GNSS Capabilities
The Micro-JLT GNSS™ is capable of simultaneously receiving up to three concurrent GNSS
systems at one time. Concurrent GNSS operation aids performance by allowing reception of up to 72
GNSS satellites in challenged reception areas such as in urban canyons, under foliage, indoors, or
close to the earth's poles, etc. Using multiple GNSS systems also increases robustness by not relying
on a single GNSS system. Several of the systems operate at different carrier frequencies, so using
multiple GNSS systems can increase immunity against jamming which often occurs at only one
carrier frequency.
The multiple GNSS systems each have their own reference time and representation of UTC. For
example, GPS uses the GPS time standard and provides a method to convert GPS time to UTC as
defined by the US Naval Observatory (USNO). GLONASS, Galileo and BeiDou have similar
reference times and UTC definitions. The Micro-JLT GNSS™ automatically adjusts for offsets
between the different GNSS time reference standards and synchronizes the 1PPS output to UTC
(USNO) when GPS is being received. If GPS is not being received, the 1PPS output is synchronized
to the best representation of UTC (USNO) available.
The selection of GNSS systems is made with the GPS:SYST:SEL command as detailed in
Section 3.3.33 . Because these systems operate at different carrier frequencies with different
bandwidths, it is necessary to use a GNSS antenna that is designed to receive all the required GNSS
systems. Please note that the new and emerging Galileo system is now functional, and uses the same
carrier frequency as GPS L1, albeit with a wider bandwidth. In our experience Galileo sats can be
received with good C/No carrier to noise figures (>40dB) with standard legacy GPS antennae and
distribution amplifiers/splitters. JLT thus recommends enabling at a minimum GPS and Galileo
concurrently with the command: GPS:SYST:SEL GPS GAL, see also Section 3.3.33 . Using other
GNSS systems such as Glonass will require an antenna system designed to support Glonass signals.
As of November 2019, JLT received multiple reports on SBAS satellites causing timing issue on the
GPSDO units around the world. Until further notice, JLT recommends disabling the SBAS in
GPS:SYST:SEL command to avoid potential timing issue or monitoring the timing stability of
Micro-JLT GNSS™ unit if SBAS is desired.
The internal GNSS receiver can track up to three different GNSS systems concurrently, such as GPS,
Galileo, Glonass, and SBAS at the same time, however only two different carrier frequencies may be
received at any given time, so BeiDou and Glonass cannot be enabled concurrently when either GPS,
Galileo, or QZSS are simultaneously enabled as that would require tracking three different carrier
frequencies.
Attempting to configure an invalid combination of GNSS systems with the GPS:SYST:SEL
command will result in a Command Error response with no change to the configuration.
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