๐Ÿ“ก WSPR Frame Decoding Guide (SP3RC Standard)

This encoding method is based on the excellent work of Bill Brown, WB8ELK.

๐Ÿ“‹ Telemetry Parameters Overview

The following telemetry data is transmitted in WSPR frames (SP3RC standard):

Telemetry data is transmitted in three consecutive WSPR frames:

Example of a complete set:

SP3RC JO71 33     โ†’ standard frame
Q44ASV JO71 30     โ†’ first telemetry frame (altitude + locator ext)
Q44KWU JO71 13     โ†’ second telemetry frame (temp + speed + sats)

This sequence provides full telemetry including altitude, location, temperature, speed and satellite count.

๐Ÿ” Frame Pairing Logic

Decoding is based on matching three WSPR frames transmitted in sequence, each 2 minutes apart:

All three frames must have the same LOCATOR, and the two telemetry frames must also match in flight number. All frames must be received exactly 2 minutes apart (T, T+2, T+4).

Example:

Three frames received:

Logical analysis:

Conclusion: Frames match โ€” telemetry can be fully decoded.

โœ… Quick Checklist

โ„น๏ธ Note

Note: The POWER field does not represent transmitter power. It carries telemetry data as follows:

1๏ธโƒฃ Standard Frame (Type 1)

Format: CALLSIGN LOCATOR POWER

Example: SP3RC JO71 33

coarse altitude (POWER in dBm โ†’ altitude in meters)

0dBm โ†’ 0m, 3dBm โ†’ 950m, 7dBm โ†’ 1900m, 10dBm โ†’ 2850m, 13dBm โ†’ 3800m, 17dBm โ†’ 4750m, 20dBm โ†’ 5700m, 23dBm โ†’ 6650m, 27dBm โ†’ 7600m, 30dBm โ†’ 8550m, 33dBm โ†’ 9500m, 37dBm โ†’ 10450m, 40dBm โ†’ 11400m, 43dBm โ†’ 12350m, 47dBm โ†’ 13300m, 50dBm โ†’ 14250m, 53dBm โ†’ 15200m, 57dBm โ†’ 16150m, 60dBm โ†’ 17100m

2๏ธโƒฃ First Telemetry Frame (Type 1)

Format:

CALLSIGN (6 characters, starts with Q), LOCATOR, POWER

Example: Q44ASV JO71 30

Flight Number (characters 2 and 3 of CALLSIGN):

Flight number = tens + units

Tens:

0 โ†’ 0, 1 โ†’ 10, 2 โ†’ 20, 3 โ†’ 30, 4 โ†’ 40, 5 โ†’ 50, 6 โ†’ 60, 7 โ†’ 70, 8 โ†’ 80, 9 โ†’ 90, A โ†’ 100, B โ†’ 110, C โ†’ 120, D โ†’ 130, E โ†’ 140, F โ†’ 150, G โ†’ 160, H โ†’ 170, I โ†’ 180, J โ†’ 190, K โ†’ 200, L โ†’ 210, M โ†’ 220, N โ†’ 230, O โ†’ 240, P โ†’ 250, Q โ†’ 260, R โ†’ 270, S โ†’ 280, T โ†’ 290, U โ†’ 300, V โ†’ 310, W โ†’ 320, X โ†’ 330, Y โ†’ 340, Z โ†’ 350

Units:

0 โ†’ 0, 1 โ†’ 1, 2 โ†’ 2, 3 โ†’ 3, 4 โ†’ 4, 5 โ†’ 5, 6 โ†’ 6, 7 โ†’ 7, 8 โ†’ 8, 9 โ†’ 9

Superfine Altitude (character 4 of CALLSIGN):

Each letter increases altitude by 2 meters.

A โ†’ 0m, B โ†’ 2m, C โ†’ 4m, D โ†’ 6m, E โ†’ 8m, F โ†’ 10m, G โ†’ 12m, H โ†’ 14m, I โ†’ 16m, J โ†’ 18m, K โ†’ 20m, L โ†’ 22m, M โ†’ 24m, N โ†’ 26m, O โ†’ 28m, P โ†’ 30m, Q โ†’ 32m, R โ†’ 34m, S โ†’ 36m, T โ†’ 38m, U โ†’ 40m, V โ†’ 42m, W โ†’ 44m, X โ†’ 46m, Y โ†’ 48m, Z โ†’ 50m

Locator Extension (characters 5 and 6 of CALLSIGN):

These extend the 4-character LOCATOR (e.g. JO71) to a full 6-character Maidenhead locator (e.g. JO71SV).

Fine Altitude (POWER in dBm โ†’ additional altitude in meters):

0dBm โ†’ 0m, 3dBm โ†’ 50m, 7dBm โ†’ 100m, 10dBm โ†’ 150m, 13dBm โ†’ 200m, 17dBm โ†’ 250m, 20dBm โ†’ 300m, 23dBm โ†’ 350m, 27dBm โ†’ 400m, 30dBm โ†’ 450m, 33dBm โ†’ 500m, 37dBm โ†’ 550m, 40dBm โ†’ 600m, 43dBm โ†’ 650m, 47dBm โ†’ 700m, 50dBm โ†’ 750m, 53dBm โ†’ 800m, 57dBm โ†’ 850m, 60dBm โ†’ 900m

3๏ธโƒฃ Second Telemetry Frame (Type 1)

Format: CALLSIGN (6 characters), LOCATOR, POWER

Example: Q44KWU JO71 13

Flight Number

Same as in the first telemetry frame: characters 2โ€“3 of the CALLSIGN, decoded using the same tens/units logic.

Temperature and Speed (characters 4โ€“6 of CALLSIGN)

Temperature: range โˆ’80ยฐC to +47ยฐC (step: 1ยฐC)

Speed: range 0 to 254 km/h (step: 2 km/h)

Both values are bit-packed together into characters 4โ€“6 of the CALLSIGN.

Satellite Count (POWER in dBm)

Number of satellites is encoded using the following discrete POWER steps:

0dBm โ†’ 3 sats, 3dBm โ†’ 4, 7dBm โ†’ 5, 10dBm โ†’ 6, 13dBm โ†’ 7, 17dBm โ†’ 8, 20dBm โ†’ 9, 23dBm โ†’ 10, 27dBm โ†’ 11, 30dBm โ†’ 12, 33dBm โ†’ 13, 37dBm โ†’ 14, 40dBm โ†’ 15, 43dBm โ†’ 16, 47dBm โ†’ 17, 50dBm โ†’ 18, 53dBm โ†’ 19, 57dBm โ†’ 20, 60dBm โ†’ 21

โœ… Step-by-Step Example:

Three frames received:

SP3RC JO71 33 โ€“ standard frame
Q44ASV JO71 30 โ€“ first telemetry frame
Q44KWU JO71 13 โ€“ second telemetry frame

1. Flight Number

2. Full Locator

3. Altitude

4. Temperature and Speed

5. Satellite Count

โœ… Temperature and Speed Decoding

In the second telemetry frame, the 4th, 5th, and 6th characters of the CALLSIGN (e.g. KWU) contain two important values:

To extract these values, each letter is treated as a number where: A = 0, B = 1, ..., Z = 25

The three letters are then combined into a single number, like a three-digit number in baseโ€‘26 (instead of baseโ€‘10). This gives a unique number that is used to calculate temperature and speed.

How to decode:

Example: KWU

  1. K = 10, W = 22, U = 20
  2. Combined value = 10 ร— 676 + 22 ร— 26 + 20 = 7352
  3. Temperature = 7352 รท 128 = 57 (rounded down)
    57 โˆ’ 80 = โˆ’23ยฐC
  4. Speed = 7352 % 128 = 56
    56 ร— 2 = 112 km/h