GNSS receivers
GNSS receivers
Hot, Cold, and Warm Starts
Hot, Cold, and Warm Starts A cold start means starting from scratch—no info about approximate coordinates, satellite almanacs, date, or anything else. A warm start happens when all that data is available. A hot start goes one step further—it also has ephemeris data. Startup time is measured from power-on to solution availability. A cold start usually takes around 30 seconds, a warm start takes 5–15 seconds, and a hot start just 1–2 seconds. That’s why minimizing startup time is a common goal. Ideally, you'd always want to start hot—with ephemerides. But here’s the catch: ephemeris data is valid for about 4 hours, or maybe 24 with some tricks. So it doesn’t make sense to store them for long. Where do you get fresh ephemerides? From the internet, of course. That’s where AGPS and AGNSS systems come in—they download fresh ephemerides and precise time via the internet. Since hot starts require internet access, what about warm starts? That’s possible if you store almanacs (which are valid for 1–2 months), along with approximate coordinates and the year (which don’t age as fast). But here’s the problem: when should the receiver save almanacs? If it’s during shutdown, you need to notify the receiver before cutting power—or it needs backup energy to save data. The alternative is saving data frequently, which requires special memory. Frequent writing means you need battery-backed static memory, since most flash memory degrades with heavy rewrites. That’s why some receivers use flash and don’t need a backup battery, while others use static memory that does. Cold Start Issues There’s also a quirky issue with warm starts: if you power off the receiver and then move it more than 300 km before powering it on again, it may take a long time to start. Why? Because the saved position is way off. That’s why cold starts are recommended after relocation. Most receivers have commands to force a cold start. Power Backup Types Receivers use lithium batteries or supercapacitors (also called ultracapacitors) for backup power. If you see a board with neither, it either uses flash memory or only supports cold starts. Lithium Batteries Some boards have a holder for lithium coin cells like MC621, SC621, or V364. These cells come in rechargeable and non-rechargeable types. Non-rechargeables last 1–2 years depending on humidity, battery quality (leakage current), and the receiver’s power draw. Rechargeables get topped off while the receiver is powered on and typically last 5–10 years. A major downside of lithium batteries: they can’t be shipped by air in large quantities. Lithium is flammable and can’t be extinguished with water. That’s why we ship receivers without batteries—users buy them locally. The Alternative: Supercapacitors Supercapacitors don’t need replacing, even after 10 years. They can be safely shipped by air—even in bulk—and are easier to solder. So we install them instead of batteries. However, high-capacity supercapacitors are large—often bigger than the board itself. So we use compact, lower-capacity ones. On small boards, they hold enough power for 30–60 minutes—plenty for a quick reboot or power interruption. On larger boards, the capacitors are bigger and can last 1–2 days—enough to power down overnight. So when buying a board, check what it uses: a battery holder or a supercapacitor. © Eltehs SIA 2025
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Nebulas IV UC9810
Nebulas IV UC9810 is Unicore's new generation proprietary GNSS SoC that integrates RF, baseband, and high-precision algorithms. By leveraging the 22nm process node architecture, a high-performance multi-mode baseband GNSS processor, and an embedded microprocessor, the chip delivers superb performance and maintains low power consumption. UC9810 supports 1408 channels and tracks multiple signals, including GPS L1C/A, L1C, L2C, L2P(Y), BDS B1I, B2I, B3I, B1C, B2a, B2b, L5, GLONASS G1, G2, G3, Galileo E1, E5a, E5b, E6, and QZSS L1, L2, L5, as well as the L-band. The integrated RTK matrix processing technology allows the chip to deliver enhanced all-system all-frequency centimeter-level RTK positioning and orientation. Due to its tight integration, high performance, low power consumption, and compact form factor, Nebulas IV is an ideal solution for technically demanding high-precision applications, such as drones, robotic lawn mowers, precision agriculture, surveying, mapping, intelligent driving, and timing. Nebulas IV supports a wealth of external interfaces that cover almost all common application interfaces, including DMA, timer, watchdog, battery, SDRAM, FLASH, CAN, network, UART, SPI, I2C, odometer, and freely configurable GPIOs. Key Technologies Dual-processor primary-secondary asynchronous architecture Dedicated RTK matrix processor UPF low-power technology All-system and all-frequency joint acquisition and tracking algorithm Anti-jamming capability (Jam Shield) RTKKEEP technology Features All-system all-frequency RF + baseband and high-precision algorithm integrated GNSS SoC Ultra-small size of 7 × 7 mm with a minimum PCB layout area of only 12×16 mm Ultra-low power consumption of 300mW 1408 channels and up to 100 Hz data update rate All-system all-frequency on-chip RTK positioning and dual-antenna heading Solution Supports GPS L1C/A/L1C/L2C/L2P(Y)/L5, BDS B1I/B2I/B3I/B1C/B2a/B2b, GLONASS G1/G2/G3, Galileo E1/E5a/E5b/E6, QZSS L1/L2/L5 SBASL-band Performance Channels 1408 channels Frequencies GPS L1C/A/L1C/L2C/L2P(Y)/L5 BDS B1I/B2I/B3I/B1C/B2a/B2b GLONASS G1/G2/G3 Galileo E1/E5a/E5b/E6 QZSS L1/L2/L5 SBAS L-band Dimensions 7 × 7 mm Cold Start andlt; 12 s TTFF andlt; 12 s RTK Initialization Time andlt; 5 s Positioning Accuracy Single Point Positioning (RMS) Horizontal: 1.5 m / Vertical: 2.5 m DGPS (RMS) Horizontal: 0.4 m / Vertical: 0.8 m RTK (RMS) Horizontal: 0.8 cm + 1 ppm / Vertical: 1.5 cm + 1 ppm Initialization Reliability andgt; 99.9% Differential Data RTCM V3.0, 3.1, 3.2, 3.3 Data Update Rate 100 Hz Timing Accuracy 2.5 ns (1σ) Power Consumption 300 mW (single antenna) Heading Accuracy 0.2°/1 m baseline © Eltehs SIA 2024
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Unicore UPrecise application
UPrecise application from Unicore Download, install, and run the configuration utility from Unicore (use Save As) UPRECISE-V2.0.1037 Select English language with the button CH/EN in the top of the program screen Connect the UM980/UM982 board to the USB port of your PC. It will be recognized as a new COM port in the Dropbox of UPrecise. Press the "Connect" button at the bottom of the program screen to establish a connection. Once connected, the data from the GNSS module will be displayed in the data stream box. You can pause the data stream to analyze past data or enter new configuration commands in the command line box. To send these commands to the GNSS module, press "Enter" on your PC keyboard. This functionality is useful for configuring the GNSS module for advanced applications or resetting it to its factory settings for normal GNSS usage. For more details, check the UPrecise User Manual Using UM982 module as Single Antenna GNSS for Base Station, providing RTCM data The UM982 actually comes with this mode enabled. However, if it is connected to an autopilot, it will be reconfigured to provide normal GNSS data and moving baseline yaw data for the vehicle. To connect the UM982 GNSS to a PC running Mission Planner or QGC, use a USB cable. Using UPrecise, enter the following commands into the configuration command line, followed by pressing Enter on your keyboard: GPGGA COM1 1 mode base time 60 2 2.5 rtcm1006 com3 1 rtcm1033 com3 1 rtcm1074 com3 1 rtcm1124 com3 1 rtcm1084 com3 1 rtcm1094 com3 1 Saveconfig This action will initiate a "survey-in" process to ascertain the GPS accuracy of the location. If no reconfiguration is carried out, the UM982 will restart the survey every time it is powered on. Upon completion of the survey, the UM982 will start transmitting RTCM correction data through the USB port. In the mode command above: 60 is the time in seconds that all fixes obtained by the UM982 must remain within an area of horizontal and vertical precision in order for the survey to be declared complete. 2 is the horizontal precision in meters all fixes must be within to declare the survey complete. 2.5 is the vertical precision required of all fixes for completing the survey. Reducing the precision settings will increase the total duration needed for the survey to be finished. If this approach is used on the bench, it may never finish or require extremely high precision values (i.e., less precise). Generally, the displayed values will provide precision at the decimeter level or better. Whenever the UM982 is power cycled or moved significantly (20 meters or more), this command should be reissued (followed by the saveconfig command) to initiate a new survey-in process for that particular location. Now, let's shut it down or unplug it, and open the Mission Planner. In the Mission Planner's setup tab, select the RTK/GPS input option to establish a connection with the UM982. Connect it using the COM port to which the UM982 USB port is connected. Set the baud rate to 115200 and click on the connect button. Make sure that the ublox M8/F9P autoconfig checkbox is unchecked before establishing the connection. After connecting to Mission Planner, the constellation checkboxes will become green, signifying the successful locking of satellites in the respective GNSS systems. Additionally, a bar graph displaying the strength of each constellation satellite will be presented, along with the location surveyed on a map. Once the RTK data undergoes processing by the GNSS system of the vehicle, it's status will transition to "RTK float" and subsequently to "RTK fixed" on the ground control station's heads-up display (HUD), signifying its readiness for utilization. "RTK float" indicates the usage of correction data but has not yet reached the highest level of accuracy. Resetting to factory configuration. Using a configuration command line, enter the following commands precisely and press enter on your keyboard: FRESET GPGGA COM1 0.2 GPRMC COM1 0.2 AGRICA COM1 0.2 config com1 230400 saveconfig © Eltehs SIA 2023
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What is the principle behind RTK GNSS?
RTK GNSS, short for Real-Time Kinematic Global Navigation Satellite System, is a cutting-edge satellite positioning technique that offers high-precision accuracy. It relies on the principle of calculating the distance between a base station and a field receiver or rover to determine accurate positioning. With RTK GNSS, you can achieve error margins of up to 1cm. This makes it an ideal choice for industries like construction, agriculture, and surveying, where accuracy and reliability are essential. RTK GNSS leverages multiple satellite signals by comparing signals received by the base station with those received by the rover to calculate the position of both. What’s more, the entire process works in real-time, which means that the results are displayed immediately as you collect data in the field. To summarize, RTK GNSS represents revolutionary technology that has transformed many industries by delivering dependable and precise positioning data, enabling improved efficiency and productivity. What is the principle behind RTK GNSS and how does it determine high-precision satellite positioning? If you're looking to understand real-time kinematic GNSS (RTK GNSS), it's important to understand how it works. RTK GNSS involves measuring the phase difference of carrier signals between two GNSS receivers - one is a fixed-base station that has a known position, while the other is a mobile rover receiver that needs high-precision positioning. The fixed-base station receives signals from GNSS satellites and uses its known position to generate correction data. This data is then sent in real time to the mobile rover receiver. By using this correction data, the rover receiver can eliminate the errors caused by atmospheric distortion in satellite signals, significantly improving its positioning accuracy. One of the key advantages of using RTK GNSS for applications like surveying, mapping, construction, and precision agriculture is that it can achieve centimeter-level accuracy in real-time, without the need for post-processing of data. This makes it an incredibly useful tool for real-time applications where speed and accuracy are critical. If you're looking for a reliable and efficient way to achieve high-precision positioning, RTK GNSS is definitely worth considering. What are the applications of RTK GNSS and why is high precision important in those industries? RTK GNSS (Real-Time Kinematic Global Navigation Satellite System) is a highly precise positioning technology that provides real-time positioning information with great accuracy. This technology finds its applications in various industries such as surveying, mapping, construction, precision agriculture, and unmanned aerial vehicles (UAVs). High precision positioning is of utmost importance in industries like surveying and mapping to ensure accurate placement of infrastructure and boundaries. In construction, RTK GNSS plays a vital role in ensuring accuracy in excavation, paving, and grading. Precisely placing utilities such as water mains and electrical lines, ensures a high level of accuracy. In precision agriculture, RTK GNSS is used to guide farm equipment like tractors and sprayers that can distribute seeds, fertilizers, and pesticides on precise locations, ensuring optimal yield while making use of resources efficiently and reducing waste. How does RTK GNSS work in calculating the position of both the base station and the rover and what is the benefit of real-time measurement? Are you looking for information on RTK-GNSS (Real-Time Kinematic Global Navigation System)? RTK-GNSS works on the principle of triangulation by using multiple GNSS satellites to determine the precise location of a moving vehicle. The system requires a base station with a compatible GNSS receiver to be placed at a fixed known location and another receiver to be mounted on the moving vehicle. Real-time measurement in RTK-GNSS provides several benefits in positioning and surveying applications. The instantaneous results allow for quick recognition and correction of any errors in the measurement process, reducing the time required for user intervention and increasing surveying efficiency and productivity. RTK-GNSS is a valuable tool for various applications, including precision agriculture, construction, and surveying, as it can correct any errors in the timing of the received signals, atmospheric conditions, and obstructions in the signal path, making the measurements more accurate and precise. What is the impact of RTK GNSS on industries that rely on satellite positioning and how has it improved productivity and data reliability? Real-Time Kinematic (RTK) GNSS technology has had a significant impact on various industries that rely on satellite positioning, primarily in surveying, agriculture, construction, and transportation. One of the benefits of RTK GNSS technology is that it enables more precise positioning and faster acquisition of location data compared to traditional GPS systems. This improved accuracy and speed allow for greater efficiency and productivity in these industries. In surveying and construction, RTK GNSS technology enables surveyors to quickly and accurately locate reference points, leading to faster and more precise construction projects. In agriculture, farmers can use RTK GNSS technology to create accurate maps of their fields, identify crops that need help, and optimize irrigation systems. Additionally, in transportation, the use of RTK GNSS technology in navigation systems has led to more efficient routing and reduced fuel consumption. Overall, the implementation of RTK GNSS technology has improved data reliability and accuracy in these industries, enabling them to complete projects more efficiently and effectively. This has led to better productivity, cost savings, and improved outcomes for businesses and organizations that rely on satellite positioning technology.
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u-blox GNSS module
The fastest solution rate belongs to the NEO-M9V – 50 Hz. The NEO-M9Q can withstand the highest temperature – up to 105 degrees Celsius. The NEO-M9L will have the longest production life. The single-frequency receiver with raw measurement output is the NEO-M8T The most accurate time is provided by the ZED-F9T-10B The most reliable time comes from the LEA-M8F The most accurate coordinates are delivered by the ZED-F9P The best receiver for UDR is the NEO-M9V The best receiver for ADR is the ZED-F9R The cheapest receiver is the SAM-M8Q, which also has a built-in antenna The most expensive receiver is the ZED-F9R The lowest power consumption without an antenna is the MAX-M10M The lowest power consumption with an antenna is the SAM-M10Q The smallest receiver module belongs to the MAX family, such as the MAX-M10M The largest receiver module belongs to the LEA and ZED families © Eltehs SIA 2023
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U-blox GNSS RTK and PPP
RTK Receivers Comparison: Best GNSS Solutions for Precision Agriculture, Drones, and Geopositioning When choosing the ideal RTK receiver for your needs, it's essential to understand their key characteristics. This guide provides a detailed comparison of the top single and dual-frequency RTK receivers, highlighting their features and performance. Whether you're working in precision agriculture, drone mapping, or geospatial applications, these receivers offer reliable GNSS positioning solutions. Single-Frequency RTK Receiver: NEO-M8P Product Overview: The NEO-M8P is a high-performance single-frequency RTK receiver designed for applications requiring accurate and reliable positioning. It is widely used in various industries, including agriculture, mapping, and surveying, offering excellent performance with its key features. Key Features: Fix Time: Up to 60 seconds for dual-system setups within 1 km. GPS-Only Fix Time: Up to 3.5 minutes. Operating Range: Up to 10 km from the base station. Accuracy: 2.5 cm + 1 mm per kilometer distance from the base. The NEO-M8P is perfect for projects where dual-frequency precision is not critical but still requires a high level of accuracy and reliability. Dual-Frequency RTK Receivers: ZED-F9P, ZED-F9R, and ZED-F9H Product Overview: For higher accuracy and faster fix times, the ZED-F9P, ZED-F9R, and ZED-F9H dual-frequency RTK receivers are optimal. These receivers are designed for applications that demand high-precision GNSS positioning and can be used in a variety of industries such as precision agriculture, drone surveying, and geospatial mapping. Key Features: Fix Time: Up to 10 seconds for dual-system setups. GPS-Only Fix Time: Up to 30 seconds. Operating Range: Up to 20 km from the base station with high accuracy, up to 50 km with reduced accuracy. Accuracy: 1 cm + 1 mm per kilometer distance from the base. These receivers are perfect for large-scale projects that require dual-frequency capabilities for fast and accurate positioning over long distances. What is Point Perfect (SPARTN)? The Point Perfect service, also known as SPARTN, uses the ZED-F9P and ZED-F9R receivers. It is a paid service offering horizontal accuracy of 6 cm, ideal for precise geospatial positioning. Key Features: Fix Time: Up to 45 seconds. Horizontal Accuracy: 6 cm. Regions Covered: Europe, the USA, Canada, South Korea, and Australia. Note: This service requires an additional subscription but provides reliable GNSS services with high accuracy. What is CLAS Service (Japan)? The CLAS (Centimeter-Level Augmentation Service) is an exclusive service in Japan that works with the ZED-F9P and ZED-F9R receivers. Key Features: Fix Time: Up to 70 seconds. Horizontal Accuracy: 4 cm. Service Availability: Available only in Japan. The CLAS service is an excellent choice for high-precision positioning within Japan, providing reliable GNSS data for professionals in geospatial and agricultural industries. © Eltehs SIA 2023
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U-blox GNSS modules: features, options, frequencies
NEO-M8L-xxA – this is an automotive receiver, NEO-M8L-xxB – simplified, with a regular quartz generator instead of TCXO and in a regular version. NEO-M8P-0 – works only in rover and moving base mode, NEO-M8P-2 can be used in a stationary base mode as well. NEO-M8T has an additional antenna amplifier compared to LEA-M8T. NEO-M8Q (except NEO-M8Q-01A) and SAM-M8Q have an additional antenna amplifier and filter compared to MAX-M8Q. ZED-F9T-00B – this is L1/B1I/L2/E5b/B2I, while ZED-F9T-10B is L1/B1C/L5/E5a/B2a (without receiving L2 GLONASS), i.e. they require different antennas. LEA-F9T can work in both versions (L2 and L5), but not simultaneously, choosing either L2 or L5. In addition, there is a version of LEA-F9T-10B with an extended temperature range up to +105 degrees Celsius. F9P. A version of L1/L5 is planned, similar to ZED-F9T-10B. Firmware updates Receivers LEA-6T-1, M8F, M8T, M8N, M8J, M8L, M8P, M8U, M9L, M9N, M9V, F9P, F9H, F9R, F9T, F10T support firmware updates. Actual firmware updates can be downloaded from the u-blox website for M8L, M8U, M9N, M9L, M9V, F9P, F9H, F9R. For these receivers, it is recommended to check the firmware version, and if it is not the latest – update it. Passive antennas and EMI protection As described in the interference section, good protection from out-of-band interference requires two filters and a protective case around the receiver and high-frequency circuits. Any active antenna necessarily has both a filter (SAW) and an amplifier (LNA), so active antennas provide good protection in combination with a filter in the receiver or on the board. All dual-frequency Ublox receivers (F9 and F10 series) can only be used with active antennas. Since these receivers have an internal antenna filter, they are protected from EMI. All single-frequency Ublox receivers (series 6, 7, 8, M8, M9, and M10) can be used with both active and passive antennas. Receivers 6T, M8F, NEO-M8T, M8N, NEO-M8Q, M8P, M9N, M9V, M10Q, M10S (as well as the less popular M8J) have additional antenna amplifiers and filters. These receivers are most protected from interference when working with active antennas. In addition, they can successfully work with passive antennas. Receivers M8S, LEA-M8T contain only a filter. They are well protected from interference when working with active antennas, and to work with passive antennas, they need an additional amplifier on the board. Receivers MAX-M8Q, M8L, M8U (as well as the less popular M8C, M8W, M8M, NEO-M8Q-01A, M9L, M10M) do not contain either an antenna amplifier or a filter. They can work with active antennas, and to work with passive antennas, they need a filter and an amplifier on the board. Additionally, there are SAM and CAM family receivers with a built-in passive antenna. In these receivers, regardless of the model, there is an antenna filter and amplifier. Signals and frequencies Different receivers receive different signals. Frequencies and signals were described in the section L1, L2, L5, L3, AND SIMPLY L FREQUENCY BANDS Let's repeat that the best signal is the newest one, which is currently Beidou-3 (B1C and B2A), and the worst one is the oldest one, which is GLONASS. 6T: GPS/QZSS/SBAS L1 (1575.420 MHz) 8Q, 8M, 8C: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), only 1 system at a time. GPS is naturally better than GLONASS. M8P: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), BEIDOU B1I (1561.098 MHz), only 2 systems at a time. If there are corresponding RTK corrections, GPS + BEIDOU is recommended. But keep in mind that the RTK method requires an exact match of base and rover signals, so the corrections must be B1I, and B1 corrections can mean either B1I or B1C. If there are no B1I corrections, then traditionally, GPS and GLONASS. M8F: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), EIDOU B1I (1561.098 MHz), only 2 systems at a time. For greater accuracy, GPS+BEIDOU is better. As for spoofing... script kiddies usually can spoof only GPS, so for anti-spoofing, GLONASS+BEIDOU is better. M8S, M8C, M8Q, M8W, M8T, M8J, M8M, M8N, M8L, M8U: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz), BEIDOU B1I (1561.098 MHz) – only 3 systems at a time. It is best to abandon GLONASS and use GPS + GALILEO + BEIDOU. However, if spoofing is expected, it is better to reject GPS since most spoofers can only spoof it. M9L, M9N, M9V: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz), BEIDOU B1I (1561.098 MHz) – all 4 systems simultaneously. M10M, M10S: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz), BEIDOU B1I (1561.098 MHz) / B1C (1575.420 MHz) – all 4 systems simultaneously. M10Q: GPS/QZSS/SBAS L1 (1575.420 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz), BEIDOU B1C (1575.420 MHz) – all 4 systems simultaneously. For M9/M10, it is better to use all systems. However, if spoofing is expected, it is better to reject GPS, as most spoofers can only spoof it. As for choosing between B1I and B1C, B1C is more accurate, and there are 1.5 times more satellites with B1I. So, for solution availability in urban canyons, B1I is better, while for accuracy, B1C is preferred. F9P, F9H, F9R: GPS/QZSS/SBAS L1 (1575.420 MHz) / L2 (1227.600 MHz), GLONASS G1 (1598.062-1605.375 MHz) / G2 (1242.937-1248.625 MHz), GALILEO E1 (1575.420 MHz) / E5B (1207.140 MHz), BEIDOU B1I (1561.098 MHz) / B2I (1207.140 MHz) - dual-frequency L1/L2/E5B, nothing to choose here ZED-F9T-00B: GPS/QZSS/SBAS L1 (1575.420 MHz) / L2 (1227.600 MHz), GLONASS G1 (1598.062-1605.375 MHz) / G2 (1242.937-1248.625 MHz), GALILEO E1 (1575.420 MHz) / E5B (1207.140 MHz), BEIDOU B1I (1561.098 MHz) / B1C (1575.420 MHz) / B2I (1207.140 MHz) – dual-frequency L1/L2/E5B, better to use B1C for higher accuracy ZED-F9T-10B: GPS/QZSS/SBAS L1 (1575.420 MHz) / L5C (1176.450 MHz), NavIC L5 (1176.450 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz) / E5A (1176.450 MHz), BEIDOU B1I (1561.098 MHz) / B1C (1575.420 MHz) / B2A (1176.450 MHz) – dual-frequency L1/L5, better to use B1C for higher accuracy and disable GLONASS entirely (since it is only on one frequency here, it does more harm than good to the solution). LEA-F9T: dual-mode. Can be used as both ZED-F9T-00B (L1/L2/E5B) and ZED-F9T-10B (L1/L5). Strongly recommended to use the L1/L5 option due to its higher accuracy. F10T: GPS/QZSS/SBAS L1 (1575.420 MHz) / L5C (1176.450 MHz), NavIC L5 (1176.450 MHz), GLONASS G1 (1598.062-1605.375 MHz), GALILEO E1 (1575.420 MHz) / E5A (1176.450 MHz), BEIDOU B1C (1575.420 MHz) / B2A (1176.450 MHz) – dual-frequency L1/L5, nothing to choose here As previously described in the L2 or L5 section, some tricks are required to receive GPS L5C. For the ZED-F9T-10B, LEA-F9T, and F10T receivers, this is described in the following application note: GPS L5 configuration © Eltehs SIA 2023
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U-blox GNSS modules linecard
GNSS Receivers Comparison: Understanding Single-frequency and RTK Models Below we will provide a brief description of the differences, and for more complete comparison tables of the models, you can read u-blox GNSS product line card. Also you can check Types of receivers section. Positioning: Single-frequency Receivers Single-frequency receivers of ordinary accuracy – all are more or less similar, differing only in options M8N, M9N – high-quality single-frequency receiver, updatable firmware, TCXO (Temperature Compensated Crystal Oscillator, provides better stability of measurements), additional antenna amplifier, and filter 8Q, M8Q, M10Q – like N, but without firmware update, 8Q also lacks an additional antenna amplifier and filter, NEO-M8Q-01A – automotive version M8J – like N, but with a regular quartz instead of TCXO 8C, M8C – like N, but without firmware update and with regular quartz (bingo!), 8C also lacks an additional antenna amplifier and filter M8W – like N, but without firmware update and additional antenna amplifier and filter, has built-in antenna power and control M8S – like W, but with an additional antenna filter M10S – like N, but without firmware update M8M, M10M – a maximally cost-reduced version (empty-empty), for those who value price over accuracy RTK: Centimeter-level Accuracy M8P, F9P – RTK receivers, M8P – single-frequency, works in RTK mode up to 10-20 kilometers from the base, F9P – dual-frequency, up to hundreds of km from the base. M8P-0 is simplified, cannot perform base functions, unlike M8P-2. RTK Heading F9H – simplified F9P for angle measurement devices. With some limitations, it can probably be used as a dual-frequency non-RTK receiver Timing Modules 6T, M8T, F9T, F10T – modules for time and frequency output. The most accurate among them is the dual-frequency F9T, which supports RTK and PPP (PointPerfect). F10T is simply dual-frequency, 6T is highly outdated. All these receivers can output raw measurements, i.e. RTK Ready (also RINEX Ready). M8F – a frequency output module with a controlled generator (VCTCXO). Unlike other receivers, it provides stable frequency over a day with 100ppb quality without GNSS reception and 5ppb during reception. It can control an external generator, measure the frequency of an external generator, etc. In short, those who need it understand why it is needed; others need to understand that this receiver is the most protected from spoofing and capable of providing accurate time for some time despite spoofing. Dead Reckoning RTK GNSS modules Ordinary meter accuracy: M9V – this is ADR + UDR, i.e. it works both with and without an odometer. Besides, this receiver can output a solution at a rate of 50 Hz. M8L, M9L – these are simplified M9V modules in automotive execution, without an additional amplifier and filter. M8L-xxB stands out as it is not automotive and is simplified due to a regular quartz generator without temperature compensation. M8U – this is a very simplified receiver, without an additional amplifier and filter, with a regular quartz generator without temperature compensation, and without an input for an odometer, i.e. it can only do UDR. High accuracy: F9R – dual-frequency RTK receiver, only supports ADR (with an odometer) © Eltehs SIA 2023
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LEA, NEO, MAX, SAM, ZED
Let's talk more specifically about u-blox receivers and their naming conventions. The name of the receiver ZED-F9P-04B-01 can be decoded as follows: ZED – family (package type), F9 – platform/generation (main chipset inside), P – receiver model, 04 – variant (received frequencies and firmware variant), B – execution (permissible operating temperatures), 01 – manufacturing details. More details available at the u-blox GNSS product overview U-blox manufacture modules in different form factors. Each form factor usually have pin-to-pin compatibility across several generations. Newer receivers can use some unused pins in older ones. LEA – package size 17.0x22.4x2.4 mm, LCC 28, interfaces – UART, USB, SPI, DDC ZED – package size 17.0x22.0x2.4 mm, LGA 54, interfaces – two UART, USB, SPI, DDC SAM – package size 15.5x15.5x6.3 mm, LGA 20, these are modules with built-in patch antenna, interfaces – UART, SPI NEO – package size 12.2x16.0x2.4 mm, LCC 24, interfaces – UART, USB, SPI, DDC CAM – package size 9.6x14.0x1.95 mm, LCC 31, these are modules with built-in patch antenna, interfaces – UART, SPI, DDC MAX – package size 9.7x10.1x2.5 mm, LCC 18, interfaces – UART, DDC For understanding, LCC stands for Leadless Chip Carrier, which is a legless chip designed for surface mounting with contacts along the edge of the chip. LGA stands for Land Grid Array, also a legless chip for surface mounting, but with contacts across the entire belly of the chip, in a square-socket manner. PCB layout for LLC is, of course, simpler, while LGA allows for more pins with the same receiver size. The ZED and LEA families are almost the same size, but the ZED has 54 LGA contacts, while the LEA has only 28 LLC contacts. The platform/generation is the type of main chipset that determines the capabilities of the receiver. In addition to this, the capabilities are also determined by the antenna, antenna amplifier, and firmware. 6, 7, 8 – these are receivers for GPS and SBAS only; in separate versions, they also support QZSS and GLONASS. These series are old and are used only in older equipment, as they say "not recommended for new designs." M8 – supports GPS/SBAS/QZSS, GLONASS, BEIDOU B1I, and on newer firmware versions, also GALILEO. You can choose 2 or 3 systems out of 4, depending on the receiver and firmware version. A total of 72 channels are received. Some M8 receivers support RTK. M9 – an improved version of M8. All 4 main systems are supported simultaneously - GPS/SBAS/QZSS, GLONASS, GALILEO, BEIDOU B1I. A total of 96 channels. M10 – a low-power version of M9. Additionally supports BEIDOU B1C (sometimes together with B1I, sometimes as a replacement). D9 – receivers for receiving correction signals. D9S – for receiving PointPerfect and other correction signals in the 1525-1559 MHz range. D9C – for receiving L2 and L6 (CLAS). F9 – dual-frequency RTK receivers. All 4 main systems are supported. Some receivers are available in two variants: L1/L2/E5B/B2I and L1/L5/E5A/B2A. A total of 184 channels. F10 – also dual-frequency receivers. More information is not available yet. © Eltehs SIA 2023
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RMS, CEP, CEP-95
Now let's talk about the most confusing part - the different accuracy parameters and their names. CEP - Circular Error Probable. This is the size of the circle into which a certain percentage of solutions fall. If no number is specified, it's CEP50, meaning that half of the solutions should fall within the circle. If "accuracy" is mentioned without any specifics, it's also CEP50, as the smallest possible option. R95 is CEP95 (equal to CEP50 multiplied by 2.08), and R99.7 is CEP99.7 (equal to CEP50 multiplied by 2.90). RMS - Root Mean Square. As Wikipedia states, it's the "square root of the arithmetic mean of the squared values." To be more precise, RMS is for one coordinate, and in a plane, it's called DRMS. It is equivalent to CEP50 multiplied by 1.2. The three-sigma rule works a bit differently here since it's for a plane. CEP50 is DRMS * 0.833, CEP95 is DRMS * 1.73, and CEP99.7 is DRMS * 2.41. DOP - Dilution of Precision. This is a family of coefficients showing how the error in measuring pseudorange to a satellite affects the distance. It's an a priori value that depends only on the geometry of satellites in the sky. PDOP is used for a plane. They are used as follows: If a receiver's specification states that CEP50 is 3 meters at PDOP 1.0, then at PDOP 2.0, the CEP50 value will be 6 meters. © Eltehs SIA 2023
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So Different Timing
Timing receivers have many different tasks. Let's look at them and the possible accuracy of their solutions. Precise time Precise time on the GPS (or GALILEO) scale can be determined by a single-frequency receiver (e.g., NEO-M8T or LEA-M8F) with a CEP50 of about 16-20 ns. This is due to ionospheric and tropospheric delays of GNSS signals. Of course, the receiver must be configured for the length of the antenna cable and consider the delays in the antenna and receiver. However, it should be understood that each satellite system has slightly different time. There are four main time references, like satellite systems. These references differ from each other by about 10 ns, and satellite systems differ from their references by another 5-10 ns. A dual-frequency receiver (e.g., ZED-F9T or F10T) independently measures and eliminates ionospheric delay, taking advantage of the fact that the delay depends on the frequency. Therefore, its accuracy is higher, approximately CEP50 at 5 ns. Precise time on the UTC scale. Each satellite system has a way to convert to UTC. But the accuracy of the least significant digit is usually 1 ns. This is because the coefficients are embedded in the satellite's board, at best, twice a day, and at worst, once a day. This results in an additional loss of about 5 ns. Synchronization. RTK (e.g., ZED-F9T) allows synchronizing two identical receivers with an accuracy of 100 ps (picoseconds). Naturally, this assumes identical antennas and accounting for cable length. However, fractional noise of 4 ns due to insufficient clock frequency of the generator interferes. In the end, the standard deviation of 2.5 ns is specified in the documentation. The disadvantage of this method is the maximum distance of hundreds of kilometers. PPP (more precisely, PointPerfect, e.g., this technology is available in ZED-F9T) enables global synchronization with the same accuracy as RTK. More precisely, PointPerfect provides accuracy within 200 ps, but the overall accuracy is determined by fractional noise, so the result is 2.5 ns. The advantage is that there are no distance limitations. Precise frequency. Here, everything is determined by fractional noise, i.e., jitter. So, ±4 ns is quite achievable for ZED-F9P, while ±11 ns is possible for NEO-N8T. Additional capabilities. Special timing receivers, like as LEA-M8F. First and foremost, this is a receiver that can adjust the frequency of its generator according to the time of the received satellite systems. Other abilities stem from this. Reliable precise time. For example, in case of a hurricane that destroys the antenna, or failures in satellite systems that occur once every ten years, or enemies with spoofers diverting precise time from your clocks (there have been such cases in high-frequency trading). By the way, most spoofers can only spoof GPS, so relying on GALILEO and BEIDOU is a good strategy. Reliable frequency - for the same reason. External generator control. This is useful if its stability is even better, for example, atomic clocks. Frequency measurement. © Eltehs SIA 2023
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Position, Heading, Timing, Dead Reckoning...
Of course, you can make a good universal receiver. But it will be an expensive "camel" (a horse made by a committee). As a rule, more specialized options are made based on a single base by making small changes to the hardware and firmware. Position. The most standard option for outputting coordinates. They come in standard and high accuracy (RTK, PPP), single-frequency and dual-frequency. Example - u-blox ZED-F9P. Heading: This is used as part of a satellite compass. That is, we place two receivers on a vehicle or vessel and measure the direction from one to the other. As a result, we get the course, roll, or differential depending on the position of the antennas. With three receivers, you can measure the course, roll, and differential. In this configuration, one receiver (base) must be F9P, while the others (rovers) should be F9H. It's better because the F9H firmware is designed for working with a moving base, while the F9P firmware in rover mode is designed for a stationary base. On the other hand, the F9H has fewer features, making it cheaper. Timing: A receiver for providing accurate time and frequency signals. Let's specifically look at an example with the same chipset - u-blox ZED-F9T and compare it with the base version - F9P. We immediately see that there are two signals instead of one, the frequency range has increased from 10 MHz to 25 MHz, and the standard deviation has improved from 30 ns to 5 ns (or 2.5 ns in differential mode). The most important thing is the jitter. In a regular receiver, the 1PPS system operates at a frequency of about 16 MHz, giving a jitter of ±30 ns, while in the F9T, it operates at 125 MHz, giving a jitter of ±4 ns. This is a real hardware modification, not just marketing tricks. On the other hand, this receiver is much worse for outputting coordinates, its autonomous mode horizontal accuracy is 2 meters CEP50 instead of 1.5 meters for F9P, and the RTK mode for coordinates is either absent or not standardized. Dead Reckoning: This allows for temporary operation in areas where there is no GNSS reception, such as tunnels. These receivers have built-in gyroscopes and accelerometers, meaning they are capable of not only satellite navigation but also inertial navigation (INS). Moreover, thanks to the INS, such a receiver can provide solutions more frequently than GNSS, making it suitable for fast processes like autonomous vehicle guidance and drones. There are two types: ADR and UDR. It's clear that such a receiver has additional hardware that makes it more expensive. ADR - Automotive Dead Reckoning: In addition to INS, a high-speed odometer is used, i.e., signals from wheel rotation sensors. This is a car system. UDR - Untethered Dead Reckoning: This is a system without an odometer, used for drones and ships. © Eltehs SIA 2023
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