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
