Pico Balloon Project

My good friend, AL7CR, and I are considering putting together a Pico Balloon system to send into the atmosphere and hopefully to travel some distance from the launch point before it ends its trip.  

This type of project is not new and many have been sent up all over the world.  In this blog I will describe the components of the project and the progress we are making toward launch.

Pico Ballons

The choice of balloons ranges from inexpensive party balloons that you can purchase at Target or stores like that.  These stores also sell the helium gas to be used to fill the balloon.  Although there are different grades of helium, a 98% pure grade will probably do the trick for us. Balloons can be latex, foil or vinyl material and range up from less than $5.00 for the party balloons to $160.00 for a scientific high altitude model.  Also, they come in different sizes up to about 36" in diameter. 

The attraction of this project includes the fact that we will include a transmitter that will send the location of the balloon using a built-in GPS receiver.  Although the transmitter produces a very low power signal, there is a network of amateur radio operators that detects the transmissions and reports the location to a central internet based network called WSPR net.  This network will track our balloon wherever it is in the world.  

Radio Transmitter

Our current plan is to use the WSPR-TX Pico Transmitter built by ZACH-TEK, a Swedish company.  The device is just the right size at 10.5 grams and is solar cell powered.  That means that when in the dark the transmitter will be quiet.

Here is the description of the transmitter.

The WSPR-TX Pico is a solar powered WSPR transmitter that is custom-made for Balloon flights.
It has the the following 

  1. Is a low power autonomous solar powered shortwave WSPR transmitter for the 20m and 30m amateur bands that continuously transmits its position and altitude during daylight. 
  2. Has an onboard GPS module and antenna for calculations of position and altitude.
  3. Runs open-source software on an Arduino compatible micro controller.
  4. The transmitter is the well known Si5351 and Phase-Locked-Loop oscillator that uses a Lab-calibrated Temperature Compensated Crystal reference Oscillator (TCXO) for exact transmissions.
  5. Weight 10.5gram
  6. Transmits its altitude using the WSPR Powerfield 
  7. Configuration is done with a Windows program. No programming skills required.
  8. Pre-built, tested and calibrated. Solar cells not soldered to PCB to make it sturdier during shipping, see assembly doc for instructions.  


  • Tranmission Frequency:
    10 and 14MHz with on-board low pass filter.
  • RF Power output:
    Slightly more than 10mWatt.
  • Size:
  • Power usage:
    0.3W (5V 20mA at idle, 60mA at transmit) Powered by solar cells or by USB to Serial converter
  • Weight:
    10.5g with solar cells

The WSPR Pico is a custom designed WSPR transmitter for balloon flights and uses the power encoding capability of he WSPR  to send its current altitude to complement the position report that is transmitted as a Maidenhed grid.  

The altitude is converted to dBm by internally dividing the altitude in meter by 300.

The result is rounded to the nearest value in dBm in the table.

To take an example - lets say the transmitter is on 11500m of altitude it will report that its power is 37dBm or 5W. (11500 divided by 300 is 38.33dBm - nearest value is 37dBm

Pico product picuture