87 lines
2.4 KiB
Markdown
87 lines
2.4 KiB
Markdown
# Airspy ADSB protocol
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**DEPRECATED**
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*This protocol is no longer used by airspy_adsb*
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## Ports
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* ??: server -> client feed
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## Format
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Textual format, similar to [raw](raw.md), but extended with MLAT and signal
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level data. Unlike raw format, lines are terminated with `\r\n` (`0x0d 0x0a`).
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## Frame structure
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* `*` (`0x2a`)
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* 7 or 14 byte frame (see [raw](raw.md))
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* `;` (`0x3b`)
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* 4 byte MLAT timestamp (see below)
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* `;` (`0x3b`)
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* 1 byte MLAT precision (see below)
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* `;` (`0x3b`)
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* 2 byte big-endian [RSSI](https://en.wikipedia.org/wiki/Received_signal_strength_indication)
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* `;\r\n` (`0x3b 0x0d 0x0a`)
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## MLAT timestamp
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The MLAT timestamp included in each frame is the big-endian value of a counter
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at the time of packet reception. The counter runs at a rate determined by the
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precision value multiplied by 2 MHz (e.g. `0x0a` means `10 * 2 MHz = 20 MHz`).
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This counter isn't calibrated to external time, but receiving software can
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calculate its offset from other receiving stations across multiple packets, and
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then use the differences between station receive timing to calculate signal
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source position.
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## Examples
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* `*5DA7DA1CE30DE5;D03B5A4B;0A;7AF3;\r\n`
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* `*` (`0x2a`): Frame start
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* `5DA7DA1CE30DE5`: Mode-S short data
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* Decoded: `0x5d 0xa7 0xda 0x1c 0xe3 0x0d 0xe5`
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* `;` (`0x3b`): Delimiter
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* `D03B5A4B`: MLAT counter
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* Decoded: `0xd0 0x3b 0x5a 0x4b`
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* Decimal: 3493550667
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* `;` (`0x3b`): Delimiter
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* `0A`: MLAT precision
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* Decoded: `0x0a`
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* Decimal: 10
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* 10 * 2 MHz = 20 MHz MLAT counter clock
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* `;` (`0x3b`): Delimiter
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* `7AF3`: RSSI
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* Decoded: `0x7a 0xf3`
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* Decimal: 31475
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* 31475 / 65535 * 100% = 48%
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* `;` (`0x3b`): Delimiter
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* `\r\n` (`0x0d 0x0a`): Frame end
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* `*8DA07CD89915908778A01E4B4C86;D03D33F9;0A;8437;\r\n`
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* `*` (`0x2a`): Frame start
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* `8DA07CD89915908778A01E4B4C86`: Mode-S long data
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* Decoded: `0x8d 0xa0 0x7c 0xd8 0x99 0x15 0x90 0x87 0x78 0xa0 0x1e 0x4b 0x4c 0x86`
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* `;` (`0x3b`): Delimiter
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* `D03D33F9`: MLAT counter
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* Decoded: `0xd0 0x3d 0x33 0xf9`
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* Decimal: 3493671929
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* `;` (`0x3b`): Delimiter
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* `0A`: MLAT precision
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* Decoded: `0x0a`
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* Decimal: 10
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* 10 * 2 MHz = 20 MHz MLAT counter clock
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* `;` (`0x3b`): Delimiter
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* `8437`: RSSI
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* Decoded: `0x84 0x37`
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* Decimal: 33847
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* 31475 / 65535 * 100% = 52%
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* `;` (`0x3b`): Delimiter
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* `\r\n` (`0x0d 0x0a`): Frame end
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## Implementations
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* [Airspy ADSB decoder](http://airspy.com/download/)
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