top of page
WSPR-TX Pico Transmitter Kit

WSPR-TX Pico Transmitter Kit

SKU: 1046

Please note that a USB to serial adapter and cable is needed to configure the WSPR-TX Pico.
This USB adapter is sold separately, see product "USB to Serial adapter and cable" - Product number 1032.

Also please note that solar cells are purchased separately.


The WSPR-TX Pico-Kit is a custom-made WSPR transmitter for Balloon flights.
This is the same product as the Pico with SKU number #1028. (
The difference is that this model is in Kit form and no test and calibration have been performed by me and thus I can sell it at a lower cost.

For first time users I would recommend getting the #1028 Pico, this version is intended as a cost reduced version for experienced balloons fliers.

But on the other hand for teachers of STEM subjects the extra soldering and testing required might be an advantage as it allows a more thorough understanding of the transmitter

The firmware is flashed so no programming is needed, only configuration of call sign and other settings.

AS mentioned the frequency calibration against a known good source have not been done on this as Pico.

Calibration is not strictly needed as the TCSO is very accurate but it can be but done by the user if so desired.


Because no calibration and tests have been done on this Kit the ground testing of the GPS and transmissions is a more essential step to perform before it’s flight.



Some quick features:

  • Low power 20mW autonomous shortwave WSPR transmitter for the 20m and 30m Amateur bands that continuously transmits its position and altitude during daylight.

  • Onboard GPS module and antenna calculates position and altitude.

  • Arduino compatible Micro-controller with open-source software and Phase-Locked-Loop oscillator with Lab-calibrated Temperature Compensated Crystal reference Oscillator (TCXO) generates transmissions.

  • Weight 5.4gram (Without solar cells, HF antenna and balloon harness)


The low output power makes it possible to operate directly from its included best-in-class lightweight polymer solar cells.

Up to 10hours of operation per day have been observed on flown prototypes.

Transmissions will get good geographical coverage as the altitude will compensate for the low output power.
Transmitting on two HF bands can increase coverage as propagation sometimes differs between the 20m and 30m Amateur bands.

Everything in the design has been weight optimized - from the very thin PCB to the lightweight Super Caps. Everything that is not needed during flights - like the USB interface - have been removed off-board.

Several generation of prototypes have been tested and flown before this final version have been adopted.

This has resulted in a transmitter with a weight of only 5.4 grams.

It contains a stable TXCO for frequency control.
Transmission is possible on either the 30m amateur band or the 20m band or on both of them.


Although WSPR Pico is a low power transmitter, great care have still been taken to ensure that no unwanted signals are generated and to that effect, it is employing a 9-pole low pass filter on the antenna output.

The focus on a clean output means that is meets the regulatory standards for suppression of overtones in all countries word-wide. (overtones are -50dBC or less)

The software (usually called Firmware in small micro-controllers like this) is open sourced and Arduino based so the end-user can modify it if needed.
This firmware have been under active development for several years and has proven to be well working and stable.
This same firmware is used in all the ZachTek WSPR transmitter products.


Although the firmware can be modified in an Arduino development software - the typical user do not want to do that and just want to fly this in his/her balloon.
I have had that in mind during the development of this and my other WSPR products and they are all intended to be “Plug-and-Play” E.g. no software skills are required and configuration is made in easy-to-use Windows software.

It can be powered from a USB to Serial adapter so the user can do test transmission if needed before taking it outside and having the solar cells power it.

USB to serial adapter and cable is needed for configuration but is sold separately, see product "USB to Serial adapter and cable" - Product number 1032


The product comes with the board mostly built but the connector and super capacitors (included) needs to be soldered on, the GPS antenna is just a short wire that also needs to be soldered in (wire not included, use any type you have at hand)
Solar cells are not included but can be purchased in the shop, several option are available that let you optimize either weight or power at low solar angles.
Build document, schema and source code are available for download from the documentation page

    bottom of page