PICO Prep & Launch

PICO Balloon Preparation and Launch Routine

Disclaimer: These suggestions are not the only methods that will work.


1.  Chinese Party Balloon, 90 cm diameter.

2.  Zach Tek, 20 meter transmitter.

3.  AWG 30 gauge magnet wire 1/2 wave dipole antenna.

4.  Kaplan tape or TYVEX house tape.

5.  Miscellaneous weights used for testing. Coins, washers, fishing weights.

6.  Precision gram scale.

7.  6 pound test braided fishing line.

8.  99.9% pure helium.  (“Party” balloon gas can be troublesome.)

9.  Controlled volume and pressure pre-streacher for pre-launch conditioning. (Option)

Transmitter/Solar Panel Tests:

1.  Attach panels and antenna to the transmitter board.

2.  Assuming the transmitter has been properly configured as per the maker’s instructions, you can probably test a VHF system by simply suspending it in an open area where the sun is shining.  The radio would wake up and start transmitting when it has a proper GPS fix.  If a HF system, the antenna is 1/2 wave of 20 meters so, for testing,  it has the upper element attached to a high point and the lower element attached to another high point or sloping down to a near-ground point.  Let the transmitter(s) operate for an hour or so.

3.  Verify that the transmitter is working by observing on board LEDs and listening to your receiver tuned to the correct frequency and by watching the WSPR and APRS websites to confirm that the signal is being received by the tracking systems.

4.  Roll each element of the 20 meter dipole onto 1/2 of a toilet paper roll core.  This allows easy transport of the system without bothersome tangles, etc.  VHF antennas, due to their size, are easier to manage.

Inflation Steps:

1.  Pre-streach the balloon envelope to 4 - 4.5 kPa.  (Optional)

2.  Prepare two simulators for testing.  Weigh every part of the payload including the transmitter, solar panels, wire, string, ribbon and all fittings like rings & swivels.  This will probably be between 12 and 18 grams.  Collect weights equal to this amount and place them in a zip-loc bag.  Include the bag weight, hollow tube weight and the weight of  any fastener clips in the total.

3.  Construct a similar simulator for the desired “free lift” weight.  It probably will be between 5 - 6 grams for a Chinese Party Balloon.

4.  Insert a hollow tube into the balloon inlet.  Tape the balloon around the tube.

5.  Slowly introduce helium into the hollow tube keeping the inside end pointed to the center of the balloon.  As the balloon fills it will start to float up from the resting surface.  At this point clip both simulator weight bags to the inlet of the balloon.  Continue introducing helium until the balloon floats in a neutral condition, neither rising or sinking.

6.  Remove the “free lift” simulator and the balloon should start to rise.  Place the balloon/simulator package near the floor and release it.  Determine the acceleration rate (change in distance / change in time) by timing the rise to about waist high.  If the time is 1 - 1.5 seconds that means the acceleration rate is approximately 1.5 m/s/s.  If the rate is faster than that you might consider letting some helium out of the balloon and if it is slower you might want to introduce more helium. This is not a very accurate way to determine actual acceleration but it gives a pretty good idea of the helium content.  


7.  Remove the payload simulator and the hollow tube.  Give the balloon a couple of quick shots of helium for good measure.  Fold and seal the inlet and apply kapton tape or TYVEX tape to the folded area.  Punch a small hole about 3mm from the bottom edge of the fold.  Your swivel hook can be inserted here or you can use a small ring, etc.  Apply a layer of tape around the final assembly.  (There are other techniques that work here.  Some use strong ribbons looped through the folds and offer an attachment point below the edge.) With the attachment point secure you are ready to launch.  The payload should be really close to the simulator weight and the balloon should try to rise.  If it does not you will have to repeat these steps starting with #5.

8. The balloon envelope may appear to not have enough helium and look to be not  inflated sufficiently.  As it rises, however, the volume of the gas will expand and the envelope will stretch to its limit.  

Launch Criteria:

1.  Weather conditions should be favorable with very low, calm winds and few clouds.  Early morning seems to work best in most areas.

2.  Transport the tested transmitter and balloon to the launch area.  It should be located away from power lines and buildings.  

3.  For an HF transmitter the antenna must be kept free from snags and trees.  A large, grassy field works well.  A 3 person team makes the launch easy to manage.  Person #1 holds the transmitter and Person #2 unrolls the upper dipole element to where Person #3 is standing with the balloon.  Person #2 snaps the upper dipole into the attachment point of the balloon and the upper element is kept elevated at all times.  Person #2 walks back to Person #1 and unrolls the lower element of the dipole in the opposite direction from Person #3.  Now the antenna is fully extended and has never touched the ground.  Person #3 releases the balloon with the attached upper dipole element.  The balloon rises toward the person holding the transmitter in the center.  When it is above the center, Person #1 releases the transmitter and the balloon/transmitter rises above the last person holding the lower element of the dipole.  When the whole assembly is above the last person the lower element is released and the balloon floats to the sky.

4.  For VHF the release process is easier due to the antenna configuration.  One person can probably manage it entirely.

5.  A properly filled the balloon will disappear from sight quickly.  If the sunlight is sufficient the transmitter location signals will begin to be received by the networks.

PICO Facts


3rd Flight Taking Off

Testing Lift in Garage

Don Giles, KM5XK

Dean Shutt, AL7CR

PICO Balloon Project 

January 2, 2021

PICO Ballooning

In February, 2020, Don attended a ham radio TechFest produced by a local ham radio group, Rocky Mountain Ham Radio-New Mexico.  I say “group” because they are not really a club and instead are simply a group of people with common interests.  They have done some interesting projects and continue to innovate.  The TechFest was composed of 7 sessions about different topics and one that caught my eye was a virtual presentation by Bill Brown of Tennessee.  He has been active in PICO ballooning for a few years and is a recognized authority.  His presentation consisted of a Power Point explanation of PICO ballooning.

PICO means “small” and is used to differentiate a segment of ballooning that is not associated with high altitude or weather balloons.  Also, it is not related to hot air ballooning that most of us are familiar with.  PICO balloons are unmanned craft and barely weigh a couple of ounces.  The payload of these flights usually weighs less than 15 grams or about 1/2 oz.  The balloons are usually 36” Chinese Party balloons and can be purchased quite inexpensively on AliExpress.  Helium is the most popular gas fill for them but some folks are using hydrogen due to the shortage of helium in the U.S.   A  Chinese Party balloon will weigh about 35 grams.  So all together there is not much mass there.

The thing that makes this all possible is a world-wide ham radio tracking system called Weak Single Propagation Reporter or WSPR.  This network of ham radio stations listens for very low powered radio signals and report to some internet based web sites when they detect a signal.  The system was not set up for ballooning but lends itself to tracking balloons around the world quite well.  A PICO balloon carries a small low wattage transmitter and a tiny GPS unit.  As it travels with the air currents around the earth, the solar powered radio transmits its location, identification and power of the transmission.  The transmitters utilize small microchips that are programmed to convert the GPS location to a Maidenhead Grid Square.  The earth is divided into Grid Squares that measure 70 x 100 miles and each has a unique identification name.  It is the grid square location that is transmitted by the small transmitter.  The receiving web site assumes that the balloon is in the center of the grid square and places it there in the tracking database that it builds.  So, as the balloon travels, it is located and tracked by about 4 or 5 different websites which can be referenced by anyone with internet capability.  The owner of the flight cannot send commands to the balloon nor can it receive actual transmissions unless the conditions are just right.  WSPR has made PICO ballooning convenient for ham radio operators to get involved with.  Our radios are currently only transmitting about .010 watts (10 mW) on the 20 meter band at 14.095.60 mHz.  That is the recognized WSPR frequency.  You probably cannot hear us on this frequency but you can surely track our progress using the websites listed below.

My friend, Dean, and I have a weekly schedule when we meet on the airwaves and talk about common interests.  I mentioned the PICO ballooning technical session to him and we immediately set up a partnership between the two of us where we decided to get started in the ballooning effort.  Originally, we were going to launch our first attempts from Oregon but the Covid 19 problem shut down commercial flying and we then decided to split up the construction tasks and to finally launch from our location in New Mexico at 7,000’.  We have, so far, launched 3 flights with pretty good success.  However, the goal is to circumvent the earth at least once so our 4th flight will include some improvements that, hopefully, will make that happen. 

Our first flight ended up near Hudson’s Bay Canada after about 5 days.  The second flight crossed the USA, the Atlantic Ocean, France, Italy and then south across the Mediterranean Sea.  Then it crossed North Africa, the Middle East and we finally lost contact with it near the Iranian/Afghanistan border.  That 18 day flight was encouraging and created lots of interest.  The third flight included some modifications and it had weather problems near Texarkana, TX where we lost contact.  We are now constructing the fourth effort and are planning for the third week in January for a launch.  The sun will be making its way north and we will have more sunlight to power the little transmitter.  Due to weight restrictions we do not have any batteries on board and rely strictly on the solar panels for power.

Dean performs the mechanical/electrical part of the payload construction while I handle the balloon section.  He mails the completed transmitter/antenna package to me and I fit it to the balloon, fill the envelope with helium and when the weather cooperates we send it off.  Once we let go of the balloon we know that we will probably never see the equipment again and the tracking system will be our only contact with it.

There are not a great number of ham radio operators involved in PICO ballooning but there is a dynamic forum on the internet where we exchange ideas and relate our experiences with flights.  The experienced guys are more than happy to share their history and give advice to newbies about these projects.  There is lots to learn about altitudes, jet streams and weather in general.  We get very familiar with the weather websites.   


  1. Radio: Zach Tek Pico transmitter.  10 mW
  2. Antenna:  20 meter half wave dipole.  AWG 30 magnet wire with 6 pound fishing line.
  3. Power:  2 solar panels fastened to the transmitter.
  4. Total weight of payload: 13.6g.
  5. Balloon:  90 cm diameter Chinese Party Balloon.  35.5g.
  6. Gas:  Industrial helium.  99.9% pure.
  7. Flight 1, KM5XK-11.  New Mexico to Hudson’s Bay, Canada.
  8. Flight 2, KM5XK-12.  New Mexico to Iran/Afghanistan border.  18 days.  26,000’.
  9. Flight 3, KM5XK-13.  New Mexico to Texas/Louisiana border.  
  10. Flight 4, KM5XK-14.  Launch scheduled for third week in February, 2021.


If you want to track our progress you can use our callsign, KM5XK, with a 2 digit suffix like -11.  The suffix changes with each flight so I will advise of each one as necessary.

  1. Toma’s blog.                                                           

     A very good, serious overview of PICO ballooning.  Tomas lived in Eastern Europe and recently passed away.  

2. WSPR Net tracking website:

    The main website for

3. Tracking website:!lat=35.47467&lng=-105.03400

    Website from Finland that tracks vehicles, boats, planes and others using     APRS.

4. VK7JJ Tracking website:

    Australian website that plots paths of balloons, etc.

5. LU7AA Tracking website:

    Terrific website from Argentina.  Originally an AMSAT centered site.

6. Zach Tek, a Swedish maker of low powered radios: 

https:  //

7. QRP Labs:

Makers of radio kits including PICO transmitters.

Balloon Pics

Here are a couple of pictures of our flights.


Early Morning Launch


Nice, clear sunlit balloon


Testing with transmitter + rolled up antenna elements.

So far, we have had 3 successful flights and plan a fourth soon.  This will be our first with a prestreached balloon.  Prestreaching consists of slowly inflating the balloon to about 4.5 kPa pressure and letting it sit fully expanded for awhile.  This pricess steaches the material and smooths out any manufacturing wrinkles, dimples and creases. Performing this prior to a launch is supposed to hopefully expand the volume slightly and allow the balloon to reach higher altitudes without bursting.  Our prestreacher consists of a couple of small aquarium pumps, flow measuring devices, and a pressure transducer.  The control is provided by a sketch residing in a Seeeduino micro controller and a Seeeduino motor control.  The speed of the pump motors can be adjusted 0 - 100% which adjusts flow and pressure of the air.  A small OLED display presents data and status information to the operator.  This prestreacher is manually operated without any automatic routines.  

Hopefully, the process will allow our flights to achieve a few extra thousands of feet.


Seeeduino V4.2 and motor control unit.


Overview showing controller, pumps, flow meter,  transducer and BOV.


Everything including the manometer used to calibrate.

Pico Balloon Project

My good friend, AL7CR, and I have been involved in a Pico Balloon project to send flights into the atmosphere and hopefully to travel some distance from the launch point before it ends its trip.  Around the globe would be really nice!!

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 of our experiment. 

Pico Ballons

The choice of balloons ranges from inexpensive Chinese party balloons that you can purchased at  AliExpress to the larger weather balloon type  and although there are different grades of helium, a 99.9%  pure grade is probably the best one to try. 

Our payload includes a transmitter that will send the location of the balloon using it's 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

We 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


Our balloons are Chinese Party balloons that we order through AliExpress.  They are quite reasonable at $1.30 each.  We prestreach these balloons prior to launch in order to extend the material to its limits.  This process is done using a controlled compressed air system that slowly admits the air to the balloon.  The prestreach control uses a Seeedurino microprocessor, two aquarium water pumps, a paddle type flow meter,  a pressure relief blow off valve and a FreeScale MPX 5010 GP pressure transducer.  The pressure transducer range is 0 - 10 kPa and is calibrated using a water manometer.  The flow meter is calibrated using a variable area flow meter that has a built-in control valve.  The operator of the prestreacher can control the speed of the pumps and also can control the flow using the valve in the flow indicator.  The operator can therefore control the rate of inflation of the balloon.