ffellowship

Frequency Fellowship: Examining Radio Wave Propagation from a High Altitude Balloon

This is a project for Hack Club's Apex, made by:

• Marcus Kauffman KN6UYL (@mineinjava)
• Hudson Hilal (@hhilal123)
• Joshua Truman (@jstruman4929)

We initially had two project ideas for Apex: this and dropping what was effectively a lawn dart from 100,000 feet. After the lawn dart project was rejected, we submitted this project.

Many high altitude balloons (HABs) have been launched, almost all of which have some sort of tracker that transmits the balloon's location. These transmissions are received by stations on the ground and then uploaded to the internet, from which we can view the locations of receiving stations for analysis. Our goal for this project is to study the differences between different tracker design techniques, specifically:

• Does radio band selection influence likelihood of reception?

  • Receiving stations on the 2m band are much more common than those on the 20m band, but 20m transmissions theoretically travel farther.

• There are three common methods of modulating signals:

  • Connecting to a dedicated radio for transmission
  • Using a MS5351M or similar clock generator IC
  • Using fancy PLL to "bit-bang" the radio waveform

  Question: do these three modulation methods have a significant difference in quality and therefore propagation?

• How do different antenna designs affect propagation.

Due to customs issues, we were only able to test the PLL tracker with three antenna wavelengths. Two of the frequencies had issues (unresolved ATM), so we instead analyzed the effect of height on radio wave propagation.

As suggested above, this project can easily be divided into three "sub-projects":

1. Use of the MS5351M Clock Generator IC.

This subproject revolves around the MS5351M clock generator. It features a custom PCB. Note that this tracker will transmit on both the 20m and 2m bands because the MS5351M has multiple clock generators.

This tracker has quite a few features, many of which are to support ultra-low power operation, as is common with this style of tracker:

• GPS
• Temperature/pressure sensor
• Shunt
• 3v3 buck-boost converter
• power supervisor to restart the pico
• Sensors can be powered off to conserve power.

This PCB is designed around the Raspberry Pi Pico due to its rigorous testing and ease of integration. It also features mainly 1206 components to aid in manual reflow soldering of the PCB.

See the dPicoTracker/ directory for more info.

2. Use of PLL:

This subproject uses the Raspberry Pi Pico to generate RF signals, without the use of a dedicated radio/chip. It is by far the simplest design and features a power supervisor, optional low-pass filter, battery measurement circuitry, as well as a GPS which is essential for correcting oscillator drift.

3. Use of a Dedicated HT Radio.

This subproject uses a Raspberry Pi Zero W and a custom PCB to connect to a HT, which will be stripped down to save weight.

The PCB consists of a voltage regulator to power the Pi and a 555 timer circuit to ensure that transmissions are limited in time (in case of a software crash).

Integration:

coming soon

Project Status:

coming soon