The QLG2-SE circuit is based around the E108-GN01 GNSS module. This module is
capable of reception of multiple satellite systems, not just GPS. This aids faster satellite
acquisition and higher sensitivity in difficult reception locations. The E108-GN01 module
uses the GK9501 GNSS chipset. Links to the datasheets for both of these are on the QRP
Labs QLG2-SE page
An active antenna module is used, having a magnetic mount, antenna patch and Low Noise
Amplifier in a weather-resistant enclosure. It is supplied with 2m of coaxial cable and an
SMA connector.
Compared to the QLG1 (former QRP Labs GPS module), which was already a highly
sensitive receiver, the QLG2-SE is even more sensitive.
The E108-GN01 GNSS module and the microcontroller require a 3.3V power supply; this is
provided from the host PC over USB, or from the host device (Ultimate3S, QCX-series
transceiver etc) which provides a 5V supply. The chosen voltage regulator is MIC5219-3.3.
The backup ultracapacitor (if installed) is charged via two 1N4148 diodes and a 1K resistor
(R4). When power to the board is removed, the ultracapacitor powers the E108-GN01’s
V_BAT pin, providing retention of the downloaded satellite ephemeris data and Real-Time
Clock. A 0.47F 5V capacitor is suitable in this application (see section above).
Level conversion from the 2.8V output of the E108-GN01 module, to the 5V logic levels
required by other QRP Labs kits, is done using a 74ACT08 quad AND-gate chip; it is not
used as an AND gate (all gates have their two inputs tied together), it is simply used as a
logic level converter. The T in the part number 74ACT08 indicates that the device has TTL
voltage threshold compatibility, and this means a “1” (logic high) is 2.4V so it is ideally
suited for accurately converting GNSS module 2.8V logic to 5V levels.
Q1 implements a simple timer which causes the yellow LED to be extinguished whenever a
‘0’ appears on the serial signal. When the signal returns to ‘1’, the capacitor C5 must
charge up via R7, until the turn-on threshold voltage of the Q1 MOSFET is reached, at
which point the yellow LED is switched on again. This simple circuit means that the data
transmission does not directly modulate the yellow Serial data LED, the LED is only lit a
small delay after the end of the data burst. This avoids generating any power line noise due
to toggling the LED at 9600 baud rate, which could be radiated into sensitive radio receivers
nearby.
5. Testing
All QLG2-SE modules are tested by QRP Labs before shipping.
The test includes:
•
Test E108-GN01 module using the supplied active GNSS patch antenna
•
Ensure time-to-first-fix (TTFF) is under 1 minute; on a sample of 20 units, the TTFF
was found to range from 23 seconds to 52 seconds, with an average of 36 seconds.
•
Check correct operation of Serial data and 1pps signals via status LEDs
These tests give a very high confidence that all QLG2-SE modules shipped by QRP Labs
will be in proper working order.
QLG2-SE manual 1.00
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