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GNSS Module Series

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EASY

™ feature works as embedded software which can accelerate TTFF by predicting satellite

navigation messages from received ephemeris. The GNSS engine automatically calculates and predicts

orbit information for up to 3 days after first receiving the broadcast ephemeris, and saves the predicted

information into the internal memory. The GNSS engine will use the information for positioning if there is

not enough information from satellites. As a result, the function is helpful for positioning and TTFF

improvement.

The EASY

™ function can reduce TTFF to 5 s in warm start. In this case, RTC domain should be valid. In

order to gain enough broadcast ephemeris information from GNSS satellites, the GNSS module should

keep tracking the information for at least 5 minutes in good signal conditions after it fixes the position.

EASY

™ function is enabled by default. For more information about the corresponding command to

disable EASY

™ function, see

document [1]

1.7.2. EPO

™

The modules all feature a function called EPO

™ (Extended Prediction Orbit) which is a world leading

technology that supports 30-day orbit predictions to customers. Occasional download from the EPO

server is needed. For more information, see

document [2]

1.8. LOCUS

These modules support the embedded logger function called LOCUS. This function can automatically log

position information to internal flash memory when enabled by dedicated LOCUS commands. With this

function, the host can save power consumption and does not need to track the NMEA information all the

time. LOCUS provides typically more log capacity without any added costs.

Software commands can be used to query the current state of LOCUS. For more information about these

commands, see

document [1]

The raw data which MCU gets must be parsed via LOCUS parser code provided by Quectel. For more

details, please contact Quectel technical support.

1.9. Multi-tone AIC

The modules all support a function called Active Interference Cancellation (multi-tone AIC) to decease

harmonic distortion of GNSS signal induced by RF signal from Wi-Fi, Bluetooth, and the 2G and 3G

networks.

Содержание L76

Страница 1: ...L76 L76 L Hardware Design GNSS Module Series Version 3 2 Date 2021 08 16 Status Released ...

Страница 2: ...claimer While Quectel has made efforts to ensure that the functions and features under development are free from errors it is possible that these functions and features could contain errors inaccuracies and omissions Unless otherwise provided by valid agreement Quectel makes no warranties of any kind implied or express with respect to the use of features and functions under development To the maxi...

Страница 3: ...smitting reproducing disseminating and editing this document as well as using the content without permission are forbidden Offenders will be held liable for payment of damages All rights are reserved in the event of a patent grant or registration of a utility model or design Copyright Quectel Wireless Solutions Co Ltd 2021 All rights reserved ...

Страница 4: ...ecautions Ensure that the product may be used in the country and the required environment as well as that it conforms to the local safety and environmental regulations Keep away from explosive and flammable materials The use of electronic products in extreme power supply conditions and locations with potentially explosive atmospheres may cause fire and explosion accidents The product must be power...

Страница 5: ...hapter 2 4 4 Changed typical voltage of V_BCKP to 3 3 V 1 2 2014 05 10 1 Modified the input power at RF_IN 2 Changed the tracking sensitivity to 165 dBm 1 3 2014 06 11 1 Updated packaging information 2 0 2014 08 28 1 Added related information of L76B module 2 Added the description of power supply requirement 2 1 2015 11 11 1 Added the description of 1PPS VS NMEA 2 Added the information about L76G ...

Страница 6: ...dated the name of PIN9 from RESET to RESET_N 6 Updated the name of PIN14 from VCC_RF to VDD_RF 7 Updated the name of PIN18 from WAKE_UP to WAKEUP 8 Added chapters 1 5 1 6 3 1 3 4 3 5 5 2 2 5 3 8 2 and 9 9 Updated the maximum altitude and accuracy of 1 PPS signal value Table 2 10 Added the GLP mode Chapter 3 3 5 11 Updated the reference design for I2C interface Figure 12 12 Updated the recommended ...

Страница 7: ... GLONASS 14 1 5 4 Galileo 15 1 5 5 QZSS 15 1 6 Augmentation System 15 1 6 1 SBAS 15 1 7 AGNSS 15 1 7 1 EASY 15 1 7 2 EPO 16 1 8 LOCUS 16 1 9 Multi tone AIC 16 2 Pin Assignment 18 3 Power Management 21 3 1 Power Unit 21 3 2 Power Supply 22 3 2 1 VCC 22 3 2 2 V_BCKP 23 3 3 Power Mode 24 3 3 1 Continuous Mode 24 3 3 2 Standby Mode 24 3 3 3 Backup Mode 25 3 3 4 Periodic Mode 26 3 3 5 GLP Mode 27 3 3 6...

Страница 8: ... Design 40 5 3 Coexistence with Cellular Systems 41 5 3 1 In Band Interference 42 5 3 2 Out of Band Interference 43 5 3 3 Ensuring Interference Immunity 43 6 Electrical Specification 45 6 1 Absolute Maximum Ratings 45 6 2 Recommended Operating Conditions 46 6 3 ESD Protection 47 7 Mechanical Dimensions 48 7 1 Top Side and Bottom View Dimensions 48 7 2 Top and Bottom Views 49 8 Product Handling 50 ...

Страница 9: ...inition 18 Table 4 Pinout 19 Table 5 Recommended Antenna Specifications 37 Table 6 Intermodulation Distortion IMD Products 43 Table 7 Absolute Maximum Ratings 45 Table 8 Recommended Operating Conditions 46 Table 9 Reel Packaging 51 Table 10 Recommended Thermal Profile Parameters 53 Table 11 Related Documents 56 Table 12 Terms and Abbreviations 56 ...

Страница 10: ...erence Design for L76 L Module 33 Figure 15 1PPS NMEA Timing 34 Figure 16 Reference OC Circuit for Module Reset 34 Figure 17 Reset Sequence 35 Figure 18 Recommended Footprint 36 Figure 19 Active Antenna Reference Design without ANTON 38 Figure 20 Reference Design for Active Antenna with ANTON 39 Figure 21 Passive Antenna Reference Design without Additional LNA 40 Figure 22 Reference Design for Pas...

Страница 11: ...erfaces I2C is only supported by L76 L module Embedded with many advanced power saving modes including GLP AlwaysLocate Standby and Backup the modules feature low power consumption in different scenes All the modules are featured with EASY technology one kind of AGNSS Capable of collecting and processing all internal aiding information like GPS time ephemeris last position etc the modules deliver ...

Страница 12: ...e versions Features L76 L76 L L76 L L Grade Industrial Automotive Category Standard Precision GNSS High Precision GNSS DR RTK Timing Supply 2 8 4 3 V Typical 3 3 V I O Typical 2 8 V Typical 1 8 V Communication Interfaces UART SPI I2C 1 Features Additional LNA Additional SAW RTC crystal TCXO oscillator 6 axis IMU Constellations GPS QZSS L1 C A L5 ...

Страница 13: ...5 SBAS L1 Temperature Range Operating temperature range 40 C to 85 C Storage temperature range 40 C to 90 C Physical Characteristics Size 10 1 0 15 mm 9 7 0 15 mm 2 5 0 20 mm Weight Approx 0 6 g Parameter Specification L76 L76 L L76 L L Power Consumption 2 Acquisition 25 mA 31 mA 31 mA Tracking 15 mA 31 mA 31 mA Standby mode 0 5 mA 0 5 mA 0 5 mA Backup mode 7 μA 8 μA 8 μA Sensitivity Acquisition 1...

Страница 14: ...be encountered 3 Open sky active high precision GNSS antenna less than 1 km baseline length 4 CEP 50 24 hours static 130 dBm more than 6 SVs Tracking 165 dBm 167 dBm 167 dBm TTFF 2 with AGNSS Cold Start 15 s 15 s 15 s Warm Start 5 s 5 s 5 s Hot Start 1 s 2 s 2 s TTFF 3 without AGNSS Cold Start 35 s 32 s 32 s Warm Start 30 s 30 s 30 s Hot Start 1 s 2 s 2 s Horizontal Position Accuracy 4 2 5 m Updat...

Страница 15: ...modules are single band GNSS receivers that can receive and track GPS BeiDou GLONASS Galileo and QZSS signals 1 5 1 GPS These modules are designed to receive and track GPS L1 C A 1574 397 1576 443 MHz signals provided by GPS 1 5 2 BeiDou They are designed to receive and track BeiDou B1I 1559 052 1563 144 MHz signals provided by the BeiDou Navigation Satellite System The ability to receive and trac...

Страница 16: ...emented by additional regional or wide area GPS enhancement data The system enhances the data through satellite broadcasting and the data can be used in GNSS receivers to improve the accuracy of the results SBAS satellites can also be used as additional signals for range or distance measurement further improving availability Supported SBAS systems include WAAS EGNOS MSAS and GAGAN 1 7 AGNSS The su...

Страница 17: ...sable EASY function see document 1 1 7 2 EPO The modules all feature a function called EPO Extended Prediction Orbit which is a world leading technology that supports 30 day orbit predictions to customers Occasional download from the EPO server is needed For more information see document 2 1 8 LOCUS These modules support the embedded logger function called LOCUS This function can automatically log...

Страница 18: ...can provide effective narrow band interference and jamming elimination The GNSS signal could be demodulated from the jammed signal which can ensure better navigation quality AIC function is enabled by default For more information about the commands that can be used to set AIC function see document 1 ...

Страница 19: ... RXD 1PPS STANDBY V_BCKP VCC RESET_N NC RESERVED I2C_SCL WAKEUP RESERVED I2C_SDA NC VDD_RF RF_IN GND ANTON GND 9 1 2 3 4 5 6 7 8 10 18 17 16 15 14 13 12 11 L76 L76 L L76 L L Top View GND POWER NC IO ANT SYSTEM Figure 2 Pin Assignment Table 3 I O Parameter Definition Type Description AI Analog Input DI Digital Input DO Digital Output DIO Digital Input Output ...

Страница 20: ...r L76 L module I2C Interface outputs NMEA data by default when reading it can also receive PMTK PQ commands through I2C bus RESERVED I2C_SCL 17 DIO For L76 L76 L L modules keep it open For L76 L module this pin is I2C_SCL ANTON 13 DO Control the ENABLE pin of additional LNA and the power supply of active antenna If unused leave the pin N C not connected STANDBY 5 DI Enter or exit from Standby mode...

Страница 21: ... VCC Typically used to supply power for an external active antenna or LNA If unused leave the pin N C not connected RF_IN 11 AI GNSS antenna interface 50 Ω characteristic impedance System RESET_N 9 DI Resets the modules Active low GND GND 1 10 12 Ground Ensures good GND connections to all GND pins of the modules with a large ground plane preferred NC NC 7 15 Not connected If unused leave the pin N...

Страница 22: ...omain powered To achieve quick startup and improve TTFF the RTC domain power supply should be valid during the interval when the VCC pin does not have a valid level SRAM memory also belongs to the RTC domain If the VCC is not valid the V_BCKP pin supplies power for SRAM memory that contains all the necessary GNSS data and some of the user configuration variables VDD_RF is an output pin equal in vo...

Страница 23: ...suring that the load current does not exceed the rated value When the modules switch from Backup mode to normal operation or startup it must charge the internal capacitors in the core domain In some cases this can lead to a significant current drain For low power applications using power saving and backup modes it is important that the LDO at the power supply or module input can provide the curren...

Страница 24: ... modules perform a cold start at power up If there is a constant power supply in your system it can be used to provide a suitable voltage to power V_BCKP V_BCKP can be directly powered by an external battery rechargeable or non rechargeable It is recommended to place a battery with the combination of a 4 7 μF a 100 nF and a 33 pF capacitor near the V_BCKP pin The figure below illustrates the refer...

Страница 25: ...completed the modules automatically switch to tracking mode In tracking mode the modules track satellites and demodulate the navigation data from specific satellites 3 3 2 Standby Mode Standby mode is a low power consumption mode In Standby mode the internal core and I O power domain are still active but RF and TCXO are powered off and the modules stop satellites search and navigation The UART int...

Страница 26: ...quires lower power consumption than Standby mode In this mode the modules stop acquiring and tracking satellites The UART is not accessible But the backed up memory in RTC domain which contains all the necessary GPS information for quick start up and a small amount of user configuration variables is maintained Due to the backed up memory EASY technology is available If the power supply to VCC pin ...

Страница 27: ...uce power consumption It contains Periodic standby mode and Periodic backup mode The modules enter or exit from the Periodic mode through software commands For more information about these commands see document 1 The following figure has shown the operation of Periodic mode When you send corresponding command the modules will be into the Continuous mode After several minutes the modules enter the ...

Страница 28: ...tering Periodic mode assure the modules are in the tracking mode otherwise the modules will have a risk of failure to track the satellite If GNSS module is located under weak signal environment it is better to set a longer Second run time to ensure the success of reacquisition 3 3 5 GLP Mode The GLP GNSS Low Power mode is an optimized solution for wearable fitness and tracking devices It reduces p...

Страница 29: ...ption Sending software command and the modules returning a corresponding command means the modules access AlwaysLocate standby mode successfully It will benefit power saving in this mode Sending software command in any time will make the modules back to Continuous mode AlwaysLocate backup mode is like AlwaysLocate standby mode The difference is that AlwaysLocate backup mode switches automatically ...

Страница 30: ...start To avoid this it is recommended to set your GPIO which controls STANDBY pin as input before the modules start After that you can reset the GPIO as output to control the STANDBY pin If it is unused keep it open 2 Keep WAKEUP pin open or low before entering AlwaysLocate backup mode Or else the AlwaysLocate backup mode will be unavailable 3 4 Power Up Sequence When VCC is powered up the modules...

Страница 31: ... ms It is recommended to use a voltage regulator that supports fast discharge To avoid abnormal voltage condition if VCC falls below specified minimum value the system must initiate a power on reset by lowering VCC to less than 100 mV for at least 100 ms UART Valid valid VCC below 100 mV 100 ms Invalid V_BCKP 50 ms below 100 mV 0 s Figure 11 Power Down Sequence ...

Страница 32: ...r firmware upgrade NMEA output and PMTK PQ proprietary messages input Supported baud rates 4800 9600 14400 19200 38400 57600 115200 230400 460800 and 921600 bps Default settings 9600 bps 8 bits no parity bit 1 stop bit Hardware flow control and synchronous operation are not supported A reference design is shown in the figure below Module TXD RXD GND Customer TXD RXD GND Figure 12 UART Interface Re...

Страница 33: ... 20 18 13 27 2 26 4 10 6 7 5 12 8 9 11 15 14 Figure 13 RS 232 Level Shift Circuit As the GNSS module outputs more data than a single GPS system the default output NMEA messages running at 4800 bps baud rate and at a 1 Hz update rate may result in data loss The solution to avoid losing data is to decrease the output NMEA types and increase the baud rate to 9600 bps 4 1 1 2 I2C Interface The L76 L m...

Страница 34: ...n Continuous mode this pin is in high level While the modules work in Standby mode GLP mode Backup mode AlwaysLocate mode and during sleep time in periodic mode this pin is in low level Based on this characteristic the ANTON pin can be used to control the power supply of active antenna or the ENABLE pin of the additional LNA to reduce power consumption 4 1 3 1PPS The 1PPS output generates one puls...

Страница 35: ...on about the commands to enable disable this function see document 1 4 1 4 System Pin 4 1 4 1 RESET_N RESET_N is an input pin The modules can be reset by driving RESET_N low for at least 100 ms and then releasing it The pin is pulled up internally by default As the power domain of RESET_N is 2 8 V 1 8 V and the pin has been pulled up inside the modules no external pull up circuit is allowed for th...

Страница 36: ...RT Valid Valid Invalid Invalid VCC V_BCKP Not cared Figure 17 Reset Sequence 1 Ensure RESET_N is connected so that it can be used to reset the modules if the modules enter an abnormal state 2 The power domain of RESET_N is 2 8 V for L76 L76 L modules 1 8 V for L76 L L module NOTE ...

Страница 37: ... The figure below describes module footprint These are recommendations not specifications 0 90 0 90 0 80 1 1 11 50 7 90 0 65 9 70 10 10 1 9 10 18 Figure 18 Recommended Footprint For easy maintenance keep a distance of at least 3 mm between the module and other components on the PCB NOTE ...

Страница 38: ...three modules A passive antenna is recommended if the antenna can be placed close to the modules for instance when the distance between the modules and the antenna is less than 1 m Otherwise use an active antenna since the insertion loss of RF cable can decrease the CNR of GNSS signal CNR is an important factor for GNSS receivers and it is defined as the ratio of the received modulated carrier sig...

Страница 39: ... System NF depends mainly on the noise figure of components and traces before first stage LNA plus noise figure of LNA itself This explains the need for using an active antenna if the antenna connection cable is too long 5 2 3 Active Antenna Reference Design 5 2 3 1 Active Antenna Reference Design without ANTON The following figure is a typical reference design of an active antenna without ANTON I...

Страница 40: ...ort circuited to the ground plane The existing footprints in the matching circuit can be used to mount other type of components than the ones presented in the figure above In that case you must pay attention to the DC power supply For example if an inductor is mounted on the C1 footprint then the circuit needs a DC blocking capacitor between L1 and C1 to prevent short circuiting of the DC power su...

Страница 41: ...ntenna Reference Design without Additional LNA The following figure is a typical reference design of a passive antenna Passive Antenna RF_IN C1 NM C2 NM R1 π Matching Circuit 0R Module D1 TVS Figure 21 Passive Antenna Reference Design without Additional LNA The components C1 R1 and C2 are reserved for matching antenna impedance By default R1 is 0 Ω while C1 and C2 are not mounted D1 is an electros...

Страница 42: ...d to use an additional LNA for L76 L and L76 L L modules because there is already an embedded LNA inside these two modules 2 The selected LNA should support both GPS and GLONASS system For more information please contact Quectel technical supports 3 The power consumption of the device can be reduced by controlling the LNA ENABLE pin through the ANTON pin of the modules If ANTON function is not use...

Страница 43: ...to the signal whose frequency is within or near the operating frequency range of a GNSS signal See the following figure for more details Power dBm 0 110 1525 1550 1575 1600 1625 Frequency MHz GPS carrier frequency 1575 42 MHz Interference signal GPS operation bands Figure 23 In Band Interference on GPS L1 The most common in band interferences usually come from Harmonics caused by crystals high spe...

Страница 44: ... 5 3 3 Ensuring Interference Immunity There are several things you can do to decrease the impact of interference signals and thus ensure the interference immunity of a GNSS receiver Keep the GNSS antenna away from interference sources Add a band pass filter in front of the GNSS module Use shielding and multi layer PCB and ensure adequate grounding Optimize layout and component placement of the PCB...

Страница 45: ... GNSS receiving antenna to ensure enough isolation Usually a good design should provide at least a 20 dB isolation between two antennas Take DCS1800 for example the maximum transmitted power of DCS1800 is around 30 dBm After a 20 dB attenuation the signal received by the GNSS antenna will be around 10 dBm which is still too high for a GNSS module With a GNSS band pass filter with around 40 dB reje...

Страница 46: ...ay cause permanent damage The product is not protected against over voltage or reversed voltage Therefore it is necessary to use appropriate protection diodes to keep voltage spikes within the parameters given in the table above Parameter Description Min Max Unit VCC Main Power Supply Voltage 0 3 4 5 V V_BCKP Backup Supply Voltage 0 3 4 5 V VIN_IO Input Voltage at I O Pins L76 L76 L 0 3 3 1 V Inpu...

Страница 47: ...O_Domain Domain Voltage at Digital I O Pins L76 L76 L 2 8 V Domain Voltage at Digital I O Pins L76 L L 1 8 V VIL Digital I O Pin Low Level Input Voltage L76 L76 L 0 3 0 7 V Digital I O Pin Low Level Input Voltage L76 L L 0 3 0 45 V VIH Digital I O Pin High Level Input Voltage L76 L76 L 2 1 3 1 V Digital I O Pin High Level Input Voltage L76 L L 1 35 2 1 V VOL Digital I O Pin Low Level Output Voltag...

Страница 48: ...d operation of any application that incorporates the modules The following measures ensure ESD protection when the modules are handled When mounting the modules onto a motherboard make sure to connect the GND first and then the RF_IN pad When handling the RF_IN pad do not come into contact with any charged capacitors or materials that may easily generate or store charges such as patch antenna coax...

Страница 49: ... three modules All dimensions are in millimeters mm The dimensional tolerances are 0 20 mm unless otherwise specified 7 1 Top Side and Bottom View Dimensions 2 5 0 15 1 0 0 10 9 7 0 15 10 1 0 15 8 84 0 10 9 18 0 10 0 65 9 70 10 10 0 90 0 80 1 10 0 50 7 90 0 65 0 65 0 65 1 9 10 18 Pin 1 Figure 26 Top Side and Bottom View Dimensions ...

Страница 50: ...s to the JEITA ED 7306 standard 7 2 Top and Bottom Views 1 18 9 10 18 10 9 1 1 9 18 18 10 10 9 1 Figure 27 Top and Bottom Views The images above are for illustrative purposes only and may differ from the actual modules For authentic appearance and label see the module received from Quectel NOTE NOTE ...

Страница 51: ...e intake and electrostatic discharge 8 1 1 Tapes The following figure shows the position of the three modules when delivered in tape and the dimensions of the tape 6 P S 1 12 1110 9 8 7 6 5 4 3 2 07 06 05 10 09 08 24 00 0 3 11 50 0 15 1 75 0 1 4 00 0 15 1 50 0 15 16 00 0 15 0 30 0 05 2 00 0 15 10 10 à0 15 3 00 à0 15 10 10 0 15 11 10 0 15 11 10 0 15 Unit mm Quantity per reel 500pcs Length per reel ...

Страница 52: ...ed in an environment where the relative humidity is less than 10 e g a drying cabinet 4 The modules should be pre baked to avoid blistering cracks and inner layer separation in PCB under the following circumstances The modules are not stored under Recommended Storage Condition Violation of the third requirement above occurs Vacuum sealed packaging is broken or the packaging has been removed for ov...

Страница 53: ...33 for the baking procedure 3 Pay attention to ESD protection such as wearing anti static gloves when touching the modules 8 3 Manufacturing and Soldering Push the squeegee to apply solder paste on the surface of stencil thus making the paste fill the stencil openings and then penetrate the PCB Apply proper force on the squeegee to produce a clean stencil surface on a single pass For more informat...

Страница 54: ... 2 3 C s Figure 29 Recommended Reflow Soldering Thermal Profile Table 10 Recommended Thermal Profile Parameters Factor Recommendation Soak Zone Max slope 1 3 C s Soak time between A and B 150 C and 200 C 70 120 s Reflow Zone Max slope 2 3 C s Reflow time D over 217 C 40 70 s Max temperature 235 C to 246 C Cooling down slope 1 5 to 3 C s Reflow Cycle Max reflow cycle 1 ...

Страница 55: ...become rusted 2 The shielding can for the modules is made of Cupro Nickel base material It is tested that after 12 hours Neutral Salt Spray test the laser engraved label information on the shielding can is still clearly identifiable and the QR code is still readable although white rust may be found 3 If a conformal coating is necessary for the modules DO NOT use any coating material that may chemi...

Страница 56: ...tion of the product type number is shown in figure below Quectel Logo Product Name Ordering Code Pin1 indication Quectel Logo Product Name Ordering Code Pin1 indication Figure 30 Labelling Information The image above is for illustrative purposes only and may differ from the actual modules For authentic appearance and label see the module received from Quectel ...

Страница 57: ... 4 Quectel_Module_Secondary_SMT_Application_Note Abbreviation Description AGNSS Assisted Global Positioning System AIC Active Interference Cancellation CEP Circular Error Probable CNR or C N Carrier to noise Ratio DCE Data Communications Equipment DCS1800 Digital Cellular System at 1800 MHz DR Dead Reckoning DTE Data Terminal Equipment EASYTM Embedded Assist System EGNOS European Geostationary Nav...

Страница 58: ...ated Circuit IC Integrated Circuit IRNSS NavIC Indian Regional Navigation Satellite System kbps kilobits per second LCC Leadless Chip Carrier package LDO Low dropout Regulator LNA Low Noise Amplifier LTE Long Term Evolution LTO Long term Orbit Mbps Megabits per second MCU Microcontroller Unit Microprogrammed Control Unit MEMS Micro Electro Mechanical System MOQ Minimum Order Quantity MP Mass Produ...

Страница 59: ...System RAM Random Access Memory RF Radio Frequency RHCP Right Hand Circular Polarization RMC Recommended Minimum Specific GNSS Data RoHS Restriction of Hazardous Substances ROM Read Only Memory RTC Real Time Clock RTK Real Time Kinematic RTS Ready to Send Request to Send RXD Receive Data 3GPP 3rd Generation Partnership Project SAW Surface Acoustic Wave SBAS Satellite Based Augmentation System SMD ...

Страница 60: ...om Access Memory TCXO Temperature Compensated Crystal Oscillator TTFF Time to First Fix TVS Transient Voltage Suppressor UART Universal Asynchronous Receiver Transmitter UTC Coordinated Universal Time VSWR Voltage Standing Wave Ratio WAAS Wide Area Augmentation System XTAL External Crystal Oscillator ...

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