top of page
WSPR-TX Pico Transmitter

WSPR-TX Pico Transmitter

SKU: 1028

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 purshased separately.


The WSPR-TX Pico is a custom-made WSPR transmitter for Balloon flights.


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.

I believe it is the most easy to use commercial Balloon WSPR tracker as all configuration is made in easy to use PC software with options you simply click to enable. No difficult commands to learn or programming to bother with.


It contains a stable TXCO for frequency control and to further improve the frequency accuracy every transmitter is individually measured and calibrated at build time.
This in turn ensures that operation in the cold environment at high altitudes will only minimally affect the transmission frequency and make sure it stays in the narrow 200Hz WSPR band.
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.

All that is required to get started besides soldering the Solar cells is to plug it in to a Windows computer and set the amateur call sign and what amateur bands to use.
After the Save button have been clicked it is ready to go on the air and will do so as soon as it has power.
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.
As soon as it has power and the GPS has figured out where it is - it will transmit.

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 built, tested and frequency calibrated against in-house Rubidium standard. Solar cells are not included but can be purchase 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