GNSS antennas
GNSS antennas
Anti Jamming
Anti-Jamming Technology in Antennas Polarization in Anti-Jamming Antennas Another trick of antennas is polarization. Signals from satellites are RHCP, meaning right-hand circular polarization. With every reflection, the polarization changes to the opposite, from right to left, from RHCP to LHCP and vice versa. Helical (Helix) and Cross-dipole antennas are designed to receive RHCP polarization much better than LHCP. This feature is called anti-jamming. Signal Reception Efficiency In the photo, you can see how RHCP signals (black) are received much better than reflected LHCP signals (red). Additionally, it’s noticeable how the reception level drops as the angle from the vertical increases. The Role of Patch Antennas and Groundplane patch antennas are not very effective at distinguishing RHCP from LHCP. Moreover, the larger the groundplane, the weaker the distinction. This does not undermine the advantages of a large groundplane; it simply does not contribute to filtering reflected signals in the upper hemisphere. Reducing Interference with Anti-Jamming Antennas Interference comes in arbitrary polarizations—linear, right-handed, or left-handed. Therefore, anti-jamming antennas receive fewer interference signals. Measuring Signal Quality with Axial Ratio The quality of the antenna is measured using a peculiar parameter called the Axial Ratio, which shows how close the antenna is to ideal polarization, where only RHCP is received. For an ideal antenna, it is 0 dB (i.e., 1). For a good antenna, it is 1-2 dB (i.e., 1.12-1.26). If this parameter is very high, it is not specified. Understanding Axial Ratio To put it into perspective, an Axial Ratio of 1 dB means a 25 dB difference in the strength between the direct and reflected signal, i.e., about 18 times in voltage and 316 times in power. An Axial Ratio of 2 dB means a 19 dB difference in signal strength, i.e., about 9 times in voltage and 80 times in power. An Axial Ratio of 3 dB means a 15 dB difference in signal strength, i.e., about 5.5 times in voltage and 30 times in power. Choosing the Best Anti-Jamming Antennas for Precision Applications If you are involved in precision agriculture, drone navigation, RTK positioning, or GNSS surveying, investing in high-performance anti-jamming antennas is essential for maintaining accuracy and reliability. In our store, you can purchase the modern, high-tech SMA Multi-Band GNSS Embedded Cross Dipole Active GNSS Antenna (ELT0148) If you need assistance in choosing the right solution, please contact our support team. © Eltehs SIA 2025
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Frequency ranges and signals.
Frequency ranges and signals Theoretical frequency ranges include: L1 Band – signals: L1/E1/B1C (1575.420 MHz) G1 (1598.062–1605.375 MHz) B1I (1561.098 MHz) L2 Band – signals: L2 (1227.600 MHz) G2 (1242.937–1248.625 MHz) L6/E6 (1278.750 MHz) B3 (1286.530 MHz) L5 Band – signals: L5/E5a/B2a (1176.450 MHz) G3 (1202.025 MHz) E5b/B2b/B2I (1207.140 MHz) Additionally, other frequency ranges are present in the antennas: L1gps Band – only signals L1/E1/B1C (1575.420 MHz), without reception of G1 GLONASS and B1I Beidou. L2b Band – signals: G3 (1202.025 MHz) E5b/B2b/B2I (1207.140 MHz) L2 (1227.600 MHz) G2 (1242.937–1248.625 MHz) L5a Band – signals: L5/E5a/B2a (1176.450 MHz) L2/L5 Band – L2+L5 signals L5/E5a/B2a (1176.450 MHz) G3 (1202.025 MHz) E5b/B2b/B2I (1207.140 MHz) L2 (1227.600 MHz) G2 (1242.937–1248.625 MHz) L6/E6 (1278.750 MHz) B3 (1286.530 MHz) L Band – signals: SPARTN (1539.8125 MHz) and other commercial correction signals. Antenna Mounts Let's consider antennas by mounting type (in brackets - supported frequency ranges) Magnetic with 3-5 meter cable: ELT0011 (L1gps) ELT0012 (L1/L2b) ELT0140 (L1/L5a) ELT0157 (L1/L2b) ELT0158 (L1/L2b) ELT0167 (L1/L2/L5) Screw mount: ELT0012 (L1/L2b) ELT0121 (L1/L2b) ELT0121W (L1/L2b) ELT0140 (L1/L5a) ELT0158 (L1/L2b) ELT0168 (L1/L2b) ELT0170 (L/L1/L2/L5) SMA connector: ELT0014 (L1/L2b) ELT0014W (L1/L2b) ELT0121 (L1/L2b) ELT0121W (L1/L2b) ELT0124 (L1) ELT0170 (L/L1/L2/L5) ELT0178 (L1/L5a) Angular SMA mount: ELT0152 (L1/L2/L5) Geodesic pole mount: ELT0123 (L1/L2/L5) Hole mount: ELT0153 (L1/L2b) Enclosure-less screw mount SMA: ELT0149 (L1/L2/L5) ELT0148 (L1/L2/L5) Enclosure-less IPEX mount: ELT0182 (L1) IPEX mount with tape: ELT0176 (L1gps) ELT0180 (L1) ELT0181 (L1) Typically, magnetic and enclosure-less antennas can also be attached using double-sided tape. Receivers and Antennas L-Band Of our antennas, only the lightweight ELT0170, which screws onto an SMA connector or can be mounted with screws, and the stationary ELT0123, which mounts on a geodetic pin, are capable of receiving signals in this band. The receiver for this range is the NEO-D9S. L1gps These antennas are suitable for NEO-M10S receivers when switching from Beidou to B1C and not using GLONASS. They also work for any other single-frequency receivers if only GPS and Galileo are being received. There are only two types of antennas: a magnetic one with a 3-meter cable and an SMA connector, ELT0011, and a caseless one with an IPEX connector, ELT0176. L1 These antennas are suitable for any single-frequency receivers. ELT0124 screws onto an SMA connector, ELT0180 and ELT0181 are adhesive with double-sided tape, while ELT0182 is mounted with screws. All except ELT0124 are caseless with an IPEX connector. L1/L2b These antennas are for dual-frequency L1/L2 receivers, such as ZED-F9P-04, ZED-F9R, ZED-F9H, ZED-F9T-00. there are magnetic options: ELT0012, ELT0157, ELT0158 screw-mounted options: ELT0012, ELT0121, ELT0121W, ELT0158, ELT0168 screw-on SMA options: ELT0014, ELT0014W, ELT0121, ELT0121W option for screwing into a hole: ELT0153 All antennas come with an SMA connector. L1/L5a These antennas are for dual-frequency L1/L5 receivers, such as ZED-F9T-00, ZED-F9P-15, NEO-F9P-15, NEO-F10T. There are only two antennas. ELT0178 screws onto an SMA connector, and ELT0140 (also with an SMA connector) can be either screw-mounted or attached to magnets. L1/L2/L5 These are multi-frequency antennas. They are used when different dual-frequency receivers (L1/L2 and L1/L5) need to be connected to one antenna, or when stationary mounting or a rare antenna type is required. There are various mounting options: magnetic ELT0167 screw-mounted ELT0170 screw-on SMA ELT0170 angled mounting on SMA ELT0152 geodetic pin mounting ELT0123 caseless screw-mountable ELT0149, ELT0148 All antennas come with an SMA connector. © Eltehs SIA 2024
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Cross dipole antennas
Cross Dipole Antennas for RTK on Drones: Maximizing Signal Quality and Stability Why Choose Cross Dipole Antennas for RTK on Drones? Cross Dipole antennas are an excellent choice for RTK applications, especially on drones, due to their superior ability to filter out reflected signals and interference. These antennas are specifically designed to provide more consistent and uniform reception, both from low and high satellites. If you're working in environments with high multipath interference, such as near buildings or on mountain slopes, a Cross Dipole antenna is your ideal solution for ensuring a reliable RTK connection. How Cross Dipole Antennas Outperform Other Antenna Types When compared to traditional antenna types like patch and helix antennas, Cross Dipole antennas stand out because they offer better resistance to interference, which is critical for applications requiring high-precision GNSS signals. Although their phase center is typically larger than that of a patch antenna, making them bulkier, their performance in challenging environments makes them worth the investment. The main disadvantage of Cross Dipole antennas is their higher cost when compared to patch and helix antennas with similar specifications. However, the extra cost is justified for users who need uncompromised performance. Key Features of ELT0148 Cross Dipole Antenna The ELT0148 is a high-performance, enclosure-less, wideband antenna designed for GNSS applications, including RTK on drones. With a frequency range covering L1/L2/L5, the ELT0148 offers excellent performance in challenging environments. Here are some of its key features: Dimensions: 42*Ø75 mm Gain: 28dB Weight: 31 grams Cable: 10 cm Connector: SMA Axial Ratio: Ranges from 1 to 1.5 dB depending on the frequency (for GLONASS G1, it's 1.9 dB). The ELT0148 antenna is particularly effective in anti-jamming situations, providing a stable RTK signal even in environments with high interference. It is mounted with four screws and ensures reliable performance for demanding GNSS applications. Why Invest in Cross Dipole Antennas for RTK Applications on Drones? Cross Dipole antennas are specifically tailored to provide superior GNSS reception on drones in difficult environments. Whether you're using drones for surveying, agriculture, or other applications requiring precise positioning, a Cross Dipole antenna ensures maximum accuracy. By choosing the right antenna like the ELT0148, you guarantee stable RTK signals with minimal interference, even in urban areas or mountainous regions with complex multipath conditions. The ability to provide consistent and clear satellite data makes these antennas an indispensable tool for professional drone operators. © Eltehs SIA 2023
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Patch antennas
Patch Antennas for GNSS and RTK Applications Patch antennas are widely used for automotive, stationary, and other precision applications like GNSS, RTK, and GPS. Known for their cost-effectiveness and high-quality performance, patch antennas are essential for accurate positioning. Though patch antennas are relatively heavier compared to alternatives like spiral (helix) antennas, they are much more affordable. One of the key advantages of patch antennas is their ability to operate efficiently on a metal ground plane, such as the roof of a vehicle. Understanding Patch Antennas and Their Applications Patch antennas are typically used in situations where the antenna must be lightweight yet durable and highly functional. They are essential in various industries including automotive, agriculture (precision farming), and surveying, especially in GNSS-based applications. Below, we review the types of patch antennas available and their corresponding features and specifications. Patch L1 GPS Antennas Patch L1 antennas are narrowband antennas that primarily receive GPS L1 signals, offering basic, cost-effective functionality for GPS receivers. These antennas have a small ground plane and are limited in their capability to receive other signals such as Galileo E1 and Beidou B1C, though they perform well in proximity to powerful transmitters. ELT0011: Magnetic mount, dimensions 48x40x13 mm, gain - 29dB, weight 42 grams (without cable), includes a 3-meter cable, SMA connector. ELT0176: Enclosure-less, wideband (L1/L2/L5), dimensions 13.4x3.4x6 mm, gain - 28dB, adhesive mount, weight 2.2 grams, 4.5 cm cable, IPEX connector. This model features an SAW filter for better protection against out-of-band interference, making it ideal for use near GSM transmitters. Patch L1 Antennas for All-Frequency GPS Receivers These antennas are perfect for single-frequency receivers as they cover all signals within the L1 range. However, they do require an external ground plane for optimal performance. ELT0180: Enclosure-less, dimensions 28x28x7 mm, gain - 33dB, adhesive mount, weight 14g, 5cm cable, IPEX connector. ELT0181: Enclosure-less, dimensions 38x38x7 mm, gain - 38dB, adhesive mount, weight 16g, 5cm cable, IPEX connector. ELT0182: Enclosure-less, dimensions Ø56x7.7 mm, gain - 28dB, screw mount, weight 34g, 5 cm cable, IPEX connector. Dual-Frequency and All-Band Patch Antennas Patch antennas designed for dual-frequency receivers, such as those operating on L1/L2 or L1/L5 frequencies, are essential for more accurate GNSS positioning in professional applications. These antennas are ideal for precise surveying, drone operations, and precision agriculture. Patch L1/L2b Antennas These antennas receive dual-frequency signals, offering improved performance for receivers that work across the L1/L2 frequency bands. ELT0012: Dimensions 82x60x22.5 mm, gain - 28dB, magnetic and screw mount, weight 173 grams (including cable), 5-meter cable, SMA connector. ELT0153: Mushroom-shaped, dimensions: 46xØ66.5 mm, gain - 28dB, hole mount, weight 150 grams (without cable), 5-meter cable, TNC-K connector. ELT0157: Dimensions 63x63x25 mm, gain - 33dB, magnetic and double-sided tape mount, weight 220g, 5-meter cable, SMA connector. Patch L1/L5a Antennas These antennas provide support for dual-frequency receivers operating on both L1 and L5a frequencies, ideal for modern GNSS systems. ELT0140: Dimensions 82x60x22.5 mm, gain - 29dB, magnetic and screw mount, weight 164g, 5-meter cable, SMA connector. Universal and Multi-Frequency Patch Antennas For applications requiring a broad range of frequency coverage, such as multi-band receivers, universal patch antennas are essential. These antennas are perfect for all-band or dual-band receivers, providing versatility across numerous frequency bands. Patch L1/L2/L5 Universal Antennas These antennas support a wide range of frequencies, making them perfect for all-band receivers. ELT0123: Stationary, dimensions Ø160x66.5 mm, gain - 38dB, screws onto a geodetic rod, weight 400g (without cable), 5-meter cable, TNC-K connector. ELT0149: Enclosure-less, dimensions 56x56x14.8 mm, gain - 38dB, four-screw mount, weight 95g, 20 cm cable, IPEX connector. ELT0193: Enclosure-less, dimensions Ø80x22.5 mm, gain - 38dB, four-screw mount, weight 102g, 10 cm cable, IPEX connector. ELT0194: Stationary, dimensions Ø100x36.5 mm, gain - 38dB, screw/tape mount, weight 290g (without cable), 5-meter cable, TNC-K connector.
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Helix antennas. About frequency bands and signals
Helix antennas are lightweight and relatively expensive antennas for drones. With similar characteristics, a helix antenna will be lighter and more expensive than a patch antenna. Another advantage of helix antennas is their improved performance against reflected signals, which means that these antennas do not require a ground plane. Let's refresh the information about frequency bands and signals. L1 band – includes L1/E1/B1C (1575.420 MHz), G1 (1598.062-1605.375 MHz), and B1I (1561.098 MHz) signals. L2 band – includes L2 (1227.600 MHz), G2 (1242.937-1248.625 MHz), L6/E6 (1278.750 MHz), and B3 (1286.530 MHz) signals. L5 band – includes L5/E5a/B2a (1176.450 MHz), E5b/B2b/B2I (1207.140 MHz), G3 (1202.025 MHz) signals. L2b band – includes G3 (1202.025 MHz), E5b/B2b/B2I (1207.140 MHz), L2 (1227.600 MHz), G2 (1242.937-1248.625 MHz) signals. Helix 50x18 L1 ELT0124 — an antenna for the L1 band. It receives all frequencies in this band: L1/E1/B1C (1575.420 MHz), G1 (1598.062-1605.375 MHz), and B1I (1561.098 MHz), making it suitable for all single-frequency receivers. Gain: 35dB. Attaches directly to the SMA connector of the receiver board. Weight: 11 grams. Color: black. Helix 55x25 L1/L2b This antenna is for L1 and L2b bands. It receives signals: L1/E1/B1C (1575.420 MHz) G1 (1598.062-1605.375 MHz) B1I (1561.098 MHz) E5b/B2b/B2I (1207.140 MHz) G3 (1202.025 MHz) L2 (1227.600 MHz) G2 (1242.937-1248.625 MHz) Gain: 28-30dB. Suitable for ZED-F9P, ZED-F9R, ZED-F9H, ZED-F9T-00B, LEA-F9T receivers in L1/L2 mode. Not suitable for ZED-F9T-10B, LEA-F9T in L1/L5 mode, and the upcoming F10. ELT0014 — Attaches directly to the SMA connector of the receiver board. Weight: 17-19 grams. Color: black. ELT0014W — Same as ELT0014, but white. ELT0168 — Attaches with four screws, connects with a built-in cable with an SMA connector. Weight: 30 grams. Color: black. Helix 83x40 L1/L2b This antenna is for L1 and L2b bands. It receives signals: L1/E1/B1C (1575.420 MHz), G1 (1598.062-1605.375 MHz), B1I (1561.098 MHz), E5b/B2b/B2I (1207.140 MHz), G3 (1202.025 MHz), L2 (1227.600 MHz), G2 (1242.937-1248.625 MHz). Suitable for ZED-F9P, ZED-F9R, ZED-F9H, ZED-F9T-00B, LEA-F9T receivers in L1/L2 mode. Not suitable for ZED-F9T-10B, LEA-F9 T in L1/L5 mode, and the upcoming F10. The Helix 83x40 differs from the Helix 55x25 in that it has a higher gain of 35dB and a signal-to-noise ratio (S/N) that is a couple of units higher. Unfortunately, the weight is also higher – 35 grams. ELT0121 — black ELT0121W — white Helix L1/L2/L5 These antennas receive signals from all frequency bands: L1/E1/B1C (1575.420 MHz), G1 (1598.062-1605.375 MHz), B1I (1561.098 MHz), L5/E5a/B2 (1176.450 MHz), E5b/B2b/B2I (1207.140 MHz), G3 (1202.025 MHz), L2 (1227.600 MHz), G2 (1242.937-1248.625 MHz), L6/E6 (1278.750 MHz), B3 (1286.530 MHz). Suitable for any dual-frequency receivers. ELT0152 — dimensions 108x28, gain 33dB, weight 28 grams, color black. Attaches to the SMA connector of the receiver board with an angled mount, which means it can be tilted for transportation or towards the south for better reception. ELT0167 — dimensions 33x48, gain 35dB, weight 25 grams, color black. Has a 1-meter cable with an SMA connector and a magnetic mount. ELT0170 — dimensions 40x43, gain 36dB, weight 325 grams, color black. Can be attached to the SMA connector of the receiver board, with three screws, or with a magnetic mount. © Eltehs SIA 2023
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Interference (the dreaded WiFi)
GNSS signals reach the antenna at a level 100 times lower than background noise. Literally, only a few hundred photons per 1 Hz bandwidth. However, thanks to code division technology, this is sufficient for stable reception. Things get worse when the interference level is millions of times higher than the GNSS signal. This can happen when interference comes from nearby or powerful transmitters. Since this interference is not at GNSS frequencies, it is called out-of-band interference. Such interference overloads the amplifier, causing it to operate with significant distortion. If the amplifier has AGC (automatic gain control), it reduces the gain, and the weak GNSS signal simply does not reach the receiver's analyzers. Out-of-band interference is combated using surface acoustic wave (SAW) filters that allow the necessary portion of the radio signal spectrum to pass through while attenuating the unwanted portion by a thousand times. Since the filter also attenuates the useful signal several times, a low-noise amplifier (LNA) is often used in conjunction with it. If the interference level is millions of times higher, one filter is not enough, and two filters should be used – both in the active antenna and in the receiver. "We wanted to insert a WiFi dongle (USB dongle) into the receiver board. The antenna was on the roof, and we were in the car... However, until we moved the WiFi 30 centimeters away, the reception was almost nonexistent. When we moved it 60 centimeters away, the interference stopped. The interference affected not the antenna (which was separated by a metal roof), not the cable (which was coaxial), not the receiver itself (which was in a metal case), but a small section on the board – from the receiver to the antenna connector." - This is a clear example of why an antenna filter is not enough and why having a filter in the receiver is a good thing. So if you have both a GNSS receiver and a transmitter nearby, first of all, try to keep them as far apart as possible and separate them with grounded metal plates. For example, place the GNSS antenna on top of a drone, with a ground plane beneath it, and then the transmitting antenna for communication with the ground below. Also, use boards where the receiver and surrounding circuitry are enclosed in a metal case, and SAW filters are present in both the antenna and the receiver. Sources of interference can include not only WiFi but also mobile communications, drone radio control systems, and so on. Moreover, even distant powerful sources can have an impact, such as television towers or large space communication antennas. © Eltehs SIA 2023
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What is better L2 or L5 band?
Some receivers accept L1, L2, E5b/B2I signals, while others accept L1, L5/E5a/B2a signals. Which one is better? To answer this, it's essential to understand the concept of "chip" and its length. In the standard GPS L1 C/A signal, modulation occurs at a frequency of 1.023 MHz, meaning that the length of one bit of the sequence is approximately 1 microsecond, or about 300 meters. Receivers usually accept signals with an accuracy of up to 1/100 of a chip, which is about 3 meters. The GPS L2C signal has a standard chip size of 300 meters, while the GPS L5C signal has a chip size ten times smaller (and a modulation of 10.23 MHz). This not only provides reception with an accuracy of 30 cm, but it also helps deal with the urban landscape's curse - multipath. The larger the shift of the reflected signal relative to the chip size, the more distinguishable the signals are for the receiver. The smaller the shift relative to the chip size, the greater the chances that the combined, slightly shifted signal will be received. For example, a shift of the reflected signal by 30 meters is a shift of 1/10 of a chip for L2C and a whole chip for L5C. Of course, 24 satellites currently broadcast the L2C signal, and only 17 satellites broadcast the L5C signal, but this will improve with new launches. A similar situation exists for BEIDOU, with B1I and B2I signals having a chip frequency of 2.046 MHz, while B1C and B2a signals have a frequency of 10.23 MHz. Additionally, B2I is a dying signal, currently transmitted by 15 satellites, while B2a is transmitted by 29 satellites. As new satellites are launched, the ratio will shift even more. For GALILEO, nothing changes as E5a and E5b have the same chip frequency of 5.115 MHz. As for GLONASS, its chip frequency is only 0.511 MHz for both G1 and G2, so it's better not to use GLONASS at all when GALILEO and BEIDOU are available. From the antenna design perspective, the fewer the frequency bands, the simpler (and cheaper) the antenna, and the more interference is filtered out by the filters. Therefore, L1/L5 receivers are better than L1/L2/E5b receivers. However, there is a downside to every positive aspect. As of February 2023, GPS L5C is broadcast by only 17 satellites. These signals are somewhat like "Schrodinger's cat." Since these signals are for aviation (and aviation is all about redundancy), it was decided that aviation receivers would not use L5C signals until there are 24 GPS satellites broadcasting L5C (approximately in 2027). As the number of L5C signals is insufficient and relying solely on GPS L5C is not feasible, other systems are necessary. Aviation standards still do not recognize Galileo or Beidou. As a result, L5C signals are considered "unhealthy" and should not be used. On the other hand, GPS L1 C/A signals are considered healthy. Therefore, a small trick is required for receivers when receiving L5C signals: they should consider their health status from L1 C/A signals. © Eltehs SIA 2023
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L1, L2, L5, L3, and simply L frequency bands:
To be honest, when talking about frequencies, there are so many, and even more names for these frequencies. All systems, except for SBAS and QZSS, have their own unique names, which makes things complicated. Incomplete antenna descriptions add to the confusion. For instance, if an antenna is said to receive L1 GPS, it actually means it receives L1 GPS, L1 SBAS, E1 Galileo, B1C Beidou, L1 QZSS, but not necessarily B1I Beidou and L1 GLONASS. According to the ITU-R (formerly CCIR) recommendations with numbers 1901-1906, there are five frequency bands allocated for GNSS, of which three are used: 1,559-1,610 MHz, referred to as L1, E1, B1 1,215-1,300 MHz, referred to as L2, E6, B3, L6 1,164-1,215 MHz, referred to as L5, E5, B2, L3 Additionally, there are other signals outside these ranges, such as 1381.05 MHz (L3 GPS) used for nuclear explosion monitoring and 1379.9133 MHz (L4 GPS) used for ionosphere research. There's also a mixed frequency range called L2b (approximately 1,200-1,250 MHz), which includes: G3 (1202.025 MHz) E5b/B2b/B2I (1207.140 MHz) L2 (1227.600 MHz) G2 (1242.937-1248.625 MHz) L1. The frequency range received by single-frequency receivers. It consists of three parts. 1575.420 MHz: L1 GPS, also L1 SBAS, E1 Galileo, B1C Beidou, L1 QZSS 1598.062-1605.375 MHz: G1 GLONASS (also L1, L1glo, etc.). New G1 GLONASS code signals are in the same range at 1600.995 MHz. Usually, only antennas marked "L1 GLONASS" receive this sub-band. Antennas labeled "L1 GPS only" do not. 1561.098 MHz: B1I Beidou. This is the "old" signal; Beidou-2 satellites only emitted this signal. New Beidou-3 satellites emit both the "old" B1I and the "new" B1C. Currently, there are 15 Beidou-2 satellites and 29 Beidou-3 satellites in orbit. Receiving B1I increases the number of satellites by one and a half times. Fortunately, many antennas receiving L1 GPS and L1 GLONASS can also receive B1I without significant issues. 1589.742 MHz is B1-2 Beidou. This is a very old signal found on the first Beidou-2 satellites. It is not present in contemporary documents on Beidou, indicating that either this signal would have been experimental or was (and still is) military. In any case, this is an atavism. L5. The next most interesting frequency band. It is received by many dual-frequency receivers. Historically, this band was allocated for aviation navigation. 1176.450 MHz: L5 GPS, L5 SBAS, L5 QZSS, L5 NavIC, E5a Galileo, and B2a Beidou-3. Mentioning Beidou-3 means that 29 out of 44 satellites currently emit this signal. Similarly, L5 GPS signal is transmitted by 17 out of 31 satellites. 1207.140 MHz: E5b Galileo, B2I Beidou-2, and B2b Beidou-3. Currently, 15 Beidou-2 satellites emit B2I, and 29 Beidou-3 satellites emit B2b on the same frequency. 1202.025 MHz: G3 GLONASS (also L3, L3glo, etc.). It currently has no practical significance, as only two satellites are broadcasting at the moment. L2. Historically appeared before L5, but new systems (Galileo and Beidou) preferred L5. This range includes all systems mixed together. 1227.600 MHz: L2 GPS and L2 QZSS. L2 GPS broadcasts civilian L2C signal (24 out of 31 satellites) and military L2P signal, received by some civilian receivers without decoding the ephemerides transmitted on it. Dual-frequency receivers like Ublox (e.g., F9P) can receive L2C. 1242.937-1248.625 MHz: G2 GLONASS (also L2, L2glo, etc.). New G1 GLONASS code signals are in the same range at 1247.060 MHz. 1278.750 MHz: E6 Galileo and L6 QZSS. E6 Galileo is high-precision encrypted signals for commercial users. L6 QZSS primarily provides high-precision corrections (CLAS and MADOCA-PPP). 1286.530 MHz: B3 Beidou. Currently, 15 Beidou-2 satellites emit B3I, and 29 Beidou-3 satellites emit encrypted B3a signal on the same frequency. L. Also named L-band refers to the frequency range of 1525–1559 MHz, which is used by various satellites to transmit correction signals. The most interesting correction among them is PointPerfect, transmitted at frequencies of 1539.8125 MHz, 1545.26 MHz (for EU), and 1556.29 MHz (for NA). The most frequent question is "which signal is better." The best signal is the newest one, which is currently Beidou-3 (B1C and B2A), while the worst is the oldest one, which is GLONASS. The newer the satellite, the better its clock stability, more accurate ephemerides, stronger signal, and higher modulation frequency. Once the majority of the current satellites are replaced with GPS III and L1C signal is introduced, they will become the best. © Eltehs SIA 2023
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PATCH, HELIX, and others
Patch antennas: This is a relatively heavy, flat ceramic antenna that doesn't work well without a ground plane. In other words, it's not an antenna for drones or pedestrians; it's an antenna for car roofs or houses. This antenna doesn't filter reflected signals very well, but it typically has a small phase center variation (PCV), making it better for RTK. Having a ground plane means that a patch antenna won't receive reflected signals from below, but if tilted, the ground will be on the side, and reflected signals can be received. With the same quality, a patch antenna will be heavier and cheaper than a helix antenna. Helix antennas: A spiral antenna, usually with four spirals. This is a lightweight antenna that effectively filters reflected signals without a ground plane. Before using it in RTK, it's recommended to check that the chosen antenna has a small phase center. It's suitable for anything that frequently tilts—drones, pedestrians, bicycles, especially if autonomous solutions with meter-level accuracy are needed. With the same quality, a helix antenna will be lighter and more expensive than a patch antenna. Cross-dipole antennas: This type of antenna best filters reflected signals and provides more uniform reception of both low and high satellites. Its phase center size is usually larger than that of good patch antennas, but it's still suitable for RTK on a drone. An example of a rare antenna designed for a specific purpose is one that captures signals from satellites low on the horizon (up to 5 degrees from the horizon). The main downside of this type of antenna is that it's more expensive than patch and helix antennas with similar characteristics. However, if you need a lightweight (but pricey) antenna for RTK on a drone, this is the one to choose. © Eltehs SIA 2023
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Passive, active, and smart antennas
The simplest antennas are passive, meaning they don't have an amplifier. There are spiral antennas for helix antennas and ceramic plates for patch antennas. To avoid losing weak signals in long cables, they are placed close to the receiver, for example, in mobile phones and trackers. All amplification is done in the radio frequency (RF) cascade of the receiver. This is an inexpensive and straightforward solution, but the quality might not be the best. The problem is that the receiver is a microchip, which means not all elements can be implemented within it. For example, it's difficult to create a frequency filter, which is very useful for preventing the amplification of various interferences on neighboring frequencies. GNSS signals are already 100 times weaker than natural noise per 1 Hz of the spectrum. And if there is interference, say, the third harmonic of television broadcasting or satellite communication, it can cause problems. That's why filters are used. The classic example is the surface acoustic wave (SAW) filter, a distant relative of ultrasonic delay lines from tube-based color TVs and quartz generators. However, a SAW filter cannot be integrated into a microchip. It can't be grown out of silicon, and naturally, it introduces losses, meaning it weakens useful signals. So, SAW filters are used together with amplifiers, and antennas with built-in amplifiers are called active antennas. Typically, the configuration is antenna → amplifier → filter → amplifier, but other variations exist. The advantage of active antennas is that they produce a stronger signal, which can be transmitted over long cables. Some antennas have amplification up to 40 dB, meaning 10,000 times stronger, allowing for the use of 100-meter coaxial cables. The downside is that the antenna requires power, which is supplied through the same coaxial cable. Note that it's incorrect to assume that an antenna with higher amplification is better than one with lower amplification. The primary criterion is not the signal level but the signal-to-noise ratio. The more an amplifier amplifies, the more noise is added to the signal. Therefore, the amount of noise introduced by the amplifier is more important than the amplification factor, especially if the cable is not hundreds of meters long. Power supply... Supplying power through a long cable can be a pain. The cable has resistance, and part of the voltage is lost in the cable. It's not always clear what portion of the voltage is lost. Therefore, it's preferable to have a voltage regulator in the antenna, and the power supply voltage should be something like "3-5 volts." The power supply also has an advantage: by checking the current flowing to the antenna, the receiver can determine if there's a short circuit in the cables or if the antenna is connected. To do this, the receiver has certain limits for what is considered too little current (not connected) and too much current (short circuit). The antenna's supply current should fall between these boundaries, otherwise the automatic system will not work correctly. The next thought is why do we need an expensive coaxial cable? Why not place the receiver and antenna in one large housing and get the digital signal from the receiver through a cheap twisted pair? That's how SMART antennas emerged, which are essentially more receivers than antennas. As I mentioned earlier, SMART antennas are used everywhere except for timing applications. "To my shame, when we made our first SMART antenna, we didn't sufficiently isolate the receiver from the antenna itself. The local oscillator in the receiver emits radiation, and the digital part generates noise at the same frequencies. As a result, interference from the receiver was induced directly onto the RF amplifier of the antenna, amplified by it, and sent back to the receiver. No, it didn't cause direct interference, but the receiver's amplifier was operating in a mode it was not designed for and overheating. This led to the receivers failing after a couple of months." The point is, if you place the antenna and receiver in the same housing, separate their ground planes. And on the side where the antenna is located, don't mount any high-frequency or digital circuits on the board. © Eltehs SIA 2023
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Connectors: BNC, TNC, SMA, MCX, MMCX, IPEX/U.FL — what's this alphabet soup?
Connectors are divided into housing connectors (those on the receiver or antenna housing) and board connectors, which are mounted on the printed circuit board. Housing connectors include BNC, TNC, and SMA, while board connectors are MCX, MMCX, and IPEX/U.FL. The board with the housing connector is connected by a wire called a pigtail. The main difference between board connectors is that they are only good for about ten uses. That is, you assemble it, plug in the pigtail, and that's it. Housing connectors are good for hundreds or even thousands of insertions and removals. If you want to have a stationary antenna and test receivers with it, use TNC connectors and thick, expensive coaxial cables. If you occasionally want to change antennas and use cables 1-2 meters long or less, SMA will work just fine. As for board connectors, anyone can insert them. But removing them... Several times, instead of pulling out the pigtail, the MCX connector simply detached from the printed circuit board. In short, there is little force involved, and you need to know how and where to apply it. Some connectors have an RP (Reverse Polarity) version, which differs in that the male and female parts are swapped relative to the inserted (screwed-in) part. And when choosing a connector, don't forget that it must be compatible with both the impedance and the diameter of the coaxial cable. Otherwise, there will be significant losses in the connector. BNC. The full name is Bayonet Neill Concelman. Invented in the 1940s by the company Amphenol and named after the company's engineer Carl Concelman. As the name suggests, it is a bayonet connector. It is probably very familiar to many people from oscilloscopes. It is still in use, for example, in Garmin navigators. TNC stands for Threaded Neill Concelman. It's a newer connector by the same author, as the name suggests, it's threaded. The main workhorse for long cables. The fact is that in order not to dissipate the weak GNSS signal, a long cable must be thick enough. Thick cables connect well with large BNC and TNC connectors. In the picture (Photo at the top of the page), on the left is the threaded TNC, and on the right is the bayonet BNC. Both can have 75-ohm impedance and 50-ohm impedance. For GNSS, usually 50 ohms. RP-TNC, also known as RTNC. This is for understanding what Reverse Polarity is. On the left and right are the male connectors, the screw-on part. But on the right with a pin, i.e., "male" (regular TNC), and on the left with a hole - "female" (RP-TNC). SMA stands for SubMiniature version A, developed in the 1960s. This connector is designed for 500 cycles, but only when using a torque wrench with force control. SMA is always designed for 50 ohms and relatively thin cables. In the photo, there's a socket with a hole, i.e., "female." With RP-SMA, on the contrary, "female" (hole) will be on the male connector, and "male" (pin) in the socket. MCX (micro coaxial connector) and its miniature version MMCX (micro-miniature coaxial) were developed in the 1980s. In the photo, you can clearly see how small the MMCX connector is. It's a snap-on connector, usually 50 ohms, used as a board connector. U.FL is a connector from Hirose Electric Group, similar connectors from other companies are called I-PEX MHF, IPEX, IPX, AMC, UMCC... It was invented in the 1990s and is even smaller than MMCX. It's also exclusively a board connector, and only 50 ohms. I think now it's clear how to understand the purpose of an antenna by its connector? BNC and TNC are for stationary or geodetic antennas, with long and thick cables. SMA is for short cables or directly on drone connectors. IPEX, MCX, and MMCX are for mounting inside devices. © Eltehs SIA 2023
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White, black, red…
The color of the antenna housing is not the most important characteristic. However, the antenna is exposed to sunlight, and black surfaces heat up more than white ones. Therefore, in the north, black antennas are better, while in the south, white antennas are preferable. On a landslide-prone slope like this, I would prefer red antennas. If they were red, it would have been more noticeable. © Eltehs SIA 2023
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