Radiosonde tracking

What is Radiosonde? Every day, every main city sends a balloon up for weather measurements. These balloons float around until the burst and fall to the groud. On the ground they are fare game for anyone to grab, after all they are a form of rubbish at that point. This sounlds like a cool idea for “fox hunting” these transmitters.

In Melbourne it seems to be sent at 10am from the airport. As the balloon floats up it transmits GPS and a bunch of weather data. There is site - https://radiosondy.info/ - which tracks the signals from the balloons, draws them on a map as well as plots the prediction of where a balloon will fly. There is even a leaders board for those who register that they have found such a radiosonde.

1 such radio sonde was sondenumber: U2840056

I found a couple of resources on tracking these radiosondes

Looking back at sondenumber: U2840056 it says it transmits on 400.500 MHz (and the others in Melbourne transmit on 401.500 MHz) so it was time to rummage about and find a receiver I may have to pick these signals up. Finally I pulled out an old RTL-SDR USB dongle I had around, never before connected successfully to my computer, and thought let’s give it a go. And sure enough after finding that I should use GQRX and I could install it with brew

  brew cask install gqrx

I put an old scanner antenna on it, walked out the back and heard the distictive sound of a Radiosonde transmission - success. Now to build a rig to track these and actually find them.

Radiosonde fox hunting rig

  1. RTL-SDR seems a good fit
  2. the GQRX software is ok
  3. but I would need a more mobile rig, so I should look to switch to a RasPi
    1. with an external monintor and mount as well as power
  4. it would be good to have a directional antenna, maybe a yagi
  5. it would be good to also have an omni directional antenna
  6. maybe an RF switch to switch between the antennas
  7. maybe even an RF amplifier
  8. and a GPS so I could compare where I am and the Radiosonde is. This would help point the directional antenna in the right direction as well as predict how far to walk when it has finally fallen on the ground. Maybe this is a smaller headsup display on an OLED.

With my head spinning with ideas I thought it would be worth investigating some of them.

Run it on a RasPi

I think the first next step would have to be to run it on a RasPi, make sure it compiles and is performant. That and getting the Radiosonde decoder software working to get live metrics and location from the Radiosonde.

There seem to be some good resources here

Decoder

Probably would be best to decode your own signals. According to [https://www.rtl-sdr.com/tutorial-on-using-rs-to-decode-and-plot-radiosondes/}(https://www.rtl-sdr.com/tutorial-on-using-rs-to-decode-and-plot-radiosondes/) RS is the free program of choice

  • https://github.com/rs1729/RS
  • there is mention of a tutorial on https://www.happysat.nl/Zilog/decoder.html
    • which can be accessed via way back machine https://web.archive.org/web/20180909213658/http://www.happysat.nl/Zilog/decoder.html
      • the images seem to be missing but there is a bunch of install instructions which could come in handy

Antenna

Next would probably be making a resonable directional antenna, like a Tapemeasure Yagi

which sends me down the rabbit hole of how to calibrate it and weather it’s time to get something like a NanoVNA? the other thing I want to get is a TinySA Ultra! for frequency analysis! so many things, so little money and time to sort out which to play with.

RF switch

RF amplifier

RF Power meter

- 1MHZ-8000MHZ 8GHz RF power attenuation OLED display RF power meter value
  digital meter 500MHZ 3GHZ+ Sofware 10W 30DB Attenuator
- [https://www.aliexpress.com/item/1005005431698851.html](https://www.aliexpress.com/item/1005005431698851.html)

RTL-SDR software

for Mac

according to https://www.rtl-sdr.com/tag/macos/

  • LocalRadio https://github.com/dsward2/LocalRadio - seems out of date
  • waveSDR - also fairly old https://github.com/getoffmyhack/waveSDR YouTube - MacOS Desktop RTLSDR Application written in Swift by GetOffMyHack MacOS Desktop RTLSDR Application written in Swift by GetOffMyHack

Morse practice key

Keen to bring some of this interest into my scout troop. The idea is to bring a morse code practice key to a scout meeting. Then slowly build on the idea:

Center tapped transformer audio oscillator

https://www.next.gr/circuits/CENTER-TAPPED-TRANSFORMER-AUDIO-OSCILLATOR-l53755.html

The oscillator circuit uses a center-tapped transistor output transformer to serve as a load for the collector of Q1, supply a feedback signal for the base, and serve as the output winding for driving the speaker. R1 supplies dc bias and C1 completes the ac path from the transformer to Q1’s base. You can play around with the values of C1 and R1 to change the oscillator’s output level and tone, but don’t reduce R1’s value too much or the transistor will draw excessive collector current.

How To DIY A Morse Code Practice Oscillator?

How To DIY A Morse Code Practice Oscillator?

fundementally

ARRL Morse Code Oscillator

https://www.arrl.org/shop/files/pdfs/Morse%20Code%20Oscillator.pdf

basically

NightFire - code practice oscillator kit

This Code Practice Oscillator Kit is a very popular and practical device used in Ham Radio for practicing your Morse Code. It is designed as a One-Transistor, Twin-Tee, Audio Phase-Shift, Sinewave Oscillator with an Audio Amplifier on the output.

The kit produces a very clean sinewave of 700Hz

Note: 700Hz is extremely popular and very pleasing to the human ear.

https://vakits.com/code-practice-oscillator-kit-w-phono-jack-3768

Electroncis Project Design - code practice oscillator

https://www.electronics-project-design.com/CodePracticeOscillator.html

another 555 based design

Morse code decoder

Jaycar has one https://www.jaycar.com.au/morse-code-decoder using a 567 Tone Decoder IC