Radio sonde

Finding a radio sonde

(december 2023)
I have for a while been interested in finding radiosondes.
Other radio amateurs like OZ5N has found 21 and OZ2OE has found 13 of these sondes.
The weather sondes interested to us here in Jylland, Denmark are launched at Karup airport every workday at 9:00.

Here a nice YouTube from Andreas Spies explaining all this so nice.

On 2023-12-11 a sonde landed near Aarhus near where my daughter lives.
On 2023-12-16 the status of the sondes was still UNKNOWN, so I decided to give it a try.
With the help of my grandson Asger (10 years) we went to the GPS coordinates given by the sonde.

The sonde

Here the sonde, it is a VAISALA Radiosonde RS41-SG:

VAISALA Radiosonde RS41-SG, Serial number V4251313

The “travel” of the sonde

Here the “travel” of the sonde, serial number V4251313, the pictures are found on SQ6KXY radiosonde tracker page:

Here the detailed map of the finding place:

And even closer:

The sonde was actually found under the tree. It was easy because the sonde is tracked after it landed by the near by tracking station of OZ1SKY and so the exact GPS location coordinates are known.

Here you can search for sites, mark Karup in Launch Sites

Main data of the sonde

Main data of the flight of the sonde:

Here my registration on SQ6KXY:

And here on sondehub tracker:


Here a picture of the PCB

Reading data of the sonde

Use a USB to TTL converter and connect it to the connector on the sonde to pin
1-GND, 2-TX and 3-RX. The connector has 2 mm pin spacing:

This is output on the serial channel when powering op the sonde, baudrate 9600:

Vaisala RS41 Radiosonde SW V2.02.15
Copyright (c) Vaisala Oyj 2016. All rights reserved.
Serial number: V4251313
Transmitter frequency: 405.30 MHz
Transmitter power: 3/7
Enabled TX

Service Mode

See here a description on how to go into the service mode to alter settings and read data without reflashing the original software
At the terminal type: <enter> STwsv <enter> (type it slowly).
This menu comes up:

(S)ensors Fre(q)uencies (P)arameters (A)lfa TX p(o)wer
TX (f)requency T(X) state (T)X registers TX contin(u)ous TX ran(d)om
TX (c)arrier (B)aud rate Ser(i)al no (R)ed LED info (N)o menu
(K)eep test mode S(W) version (M)easurements (L)aunch/Drop (E)xit
Type “x” to stop sending on TX (it is illegal to transmit on 405.300 MHz)

Type “i” to change the serial number to f. ex. your call sign
Serial number V4251313 > OZ2XH
This setting will survive reboots.

Type “s” for sensors:
RH: 42.50 RHtu: 31.27 Trh: 25.69 T: 20.62 Tref: 24.45 Tmcu: 23.68 C: 49.14 Rt: 1190.46 Rts: 1061.79 Tp: 0.031 6 Cp: 0.3663q

Type “f” for TX frequency
You can input 400-405,99 MHz

Change TX to 433,500 MHz

To change the TX for radio amateur 70 cm band you can directly access registers to change f. ex. to 433,500 MHz
Type “t” to access TX registers.
Register number (00-7F) > 75
Register value 16 > 21
Now change register 75 to 21, 76 to 02 and 77 to 67.
Unfortunately this change does not survive reboots.

Type “m” for measurements:
A new menu comes up:
(S)ensors Fre(q)uencies S(W) reset (D)efault params (U)se sensor
(R)eg offset Reg (c)heck (T) self-check St(o)p sequence (H)eat ref
(G)PS (N)MEA D(I)rect GPS mode (E)xit

Type “s” for sensors, it ask for Period 1.0 > type 5 and all sensor data are shown every 5 sec:
RH: 29.62 RHtu: 22.55 Trh: 29.81 T: 25.15 Tref: 26.76 Tmcu: 26.29 C: 48.35 Rt: 1191.21 Rts: 1079.93 Tp: 0.0545 Cp: 0.279

Maybe I will find out more later ….


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