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Russian Radionavigation System Alpha (RSDN-20)
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The Russian Alpha navaid system, formally called RSDN-20, is a VLF hyperbolic positioning system, similar to the old Omega system. Alpha was first put into service beginning in 1962, and is still in operation today. Its signals can often be heard worldwide due to the nature of radio propagation at VLF frequencies.
The system consists of five transmitters operating with power levels of 500 kW, on eight or nine different VLF frequencies. The frequencies are chosen to be mathematically optimal for hyperbolic positioning, and the geometric layout of the transmitters is optimized for coverage of the polar and North American regions.
Besides its intended use as a navigation system, the high power and low frequency of the transmitters has made them useful for ancillary scientific studies of the ionosphere and magnetosphere.
The exact frequencies of the nine Alpha signals are:
F1: 11904.76190 Hz
F2: 12648.80952 Hz
F3: 14880.95238 Hz
F3b: 14881.09127 Hz
F4: 12090.77381 Hz
F5: 12044.27083 Hz
F6: 12500.00000 Hz (rarely used)
F7: 13281.25000 Hz (rarely used)
F8: 15625.00000 Hz (rarely used)
According to some sources, only F1, F2, and F3 are currently operating, and only three of the five transmitter sites are on air.
Substantial additional information on the Alpha system is available from the references.
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Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 11.905 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F1) | Radionavigation | - |
| 12.044 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F5) | Radionavigation | - |
| 12.091 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F4) | Radionavigation | - |
| 12.5 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F6) | Radionavigation | - |
| 12.649 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F2) | Radionavigation | - |
| 13.281 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F7) | Radionavigation | - |
| 14.881 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F3) | Radionavigation | - |
| 15.625 kHz | 0.2 kHz | Russian Alpha radionavigation system (frequency F8) | Radionavigation | - |
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