Sonde Tracker³

Sonde Tracker³ is a portable radiosonde tracking device I built using off-the-shelf components. It features a 3D printed 1U CubeSat frame which is the actual size of numerous CubeSat satellites currently orbiting the Earth. The frame is highly customizable. Below I describe just one of several configurations I considered during the design process (another configuration uses 2-3 SDRs to track multiple radiosondes but eliminates the power bank).

Components

Universal 1U CubeSat – https://www.thingiverse.com/thing:4096437
Nylon Hex Spacer Standoff Kit – https://www.amzn.com/B07TP2YYQB
Raspberry Pi 4 Model B – https://www.raspberrypi.com/products/raspberry-pi-4-model-b/
GT-U7 GPS Receiver – https://www.amzn.com/B07P8YMVNT
RTL-SDR Blog V3 Dongle and Antenna Kit- https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/
403MHz Filtered Preamp – https://store.uputronics.com/index.php?route=product/product&product_id=54
10,000mAH Power Bank – https://www.amzn.com/B08L3CC222
6-inch USB 2.0 Male to Female Extension Plug – https://www.amzn.com/B01GA1GKYW
6-inch Micro USB Cable – https://www.amzn.com/B094Q9TKZR
6-inch SMA Male to SMA Male RG316 Coaxial Jumper Cable – https://www.amzn.com/B08DG7JFV7

Software

radiosonde_auto_rx – https://github.com/projecthorus/radiosonde_auto_rx
Chasemapper – https://github.com/projecthorus/chasemapper
gpsd – https://gpsd.gitlab.io/gpsd/

Assembly

The Pi is attached to a CubeSat Adaptor Mount using nylon hex nuts as standoffs. This platform is then attached to a CubeSat Bottom Frame using 27.5mm nylon standoffs (15mm + 10mm + hex nut). This provides the clearance needed for the power bank. I also placed some rubber grommets on the 27.5mm standoffs to keep the power bank securely in the frame. Above the Pi is another CubeSat Adaptor Mount that is attached using 26mm nylon spacers (20mm + 6mm). This mount has been modified so a 25mm fan can be attached from below.

The mounting holes on the Pi and the adaptor mount are 2.5 mm but the nylon screws and standoffs are 3mm, therefore the mounting holes needed to be slightly enlarged. I simply used a metal 3mm screw to enlarge and thread the holes.

Attached to the top of the fan mount are the SDR and preamp.

The SDR and preamp are held together by zip ties. The aluminum case on the SDR is designed to act like a heatsink so it is often warm to the touch. Tying it to the aluminum case on the preamp provides some additional heatsink capability.
I designed some brackets that with pins on the bottom that insert into existing holes on the adapter mount. When the rest of the frame is attached the SDR and preamp are securely held in place.
Here you can see the fan attached to the bottom of the adapter mount.

Next the rest of the frame, consisting of two CubeSat Side Frames and another CubeSat Bottom Frame, is connected to the existing CubeSat Bottom Frame using nylon 12mm screws and hex nuts. I modified one of the side frames to hold the GT-U7 GPS receiver. I also modified the additional bottom frame (which now becomes the top frame) to hold the GPS patch antenna.

I designed the GPS receiver mount with enough clearance underneath to allow for soldering wires directly to the PCB. This provides a serial connection to the GPIO pins on the Pi. The receiver mount is also offset so a USB cable could be used instead.
My patch antenna fits snugly into a mounting bracket without the need for additional support.

The equipment interconnects are pretty straightforward.

The 6-inch USB Male to Female Extension Plug connects the Pi and SDR. A 6-inch Micro USB Cable could also be used to connect the Pi and GT-U7 (see image at the top of the page).
The 6-inch SMA Male to SMA Male RG316 Coaxial Jumper Cable connects the SDR and the preamp.
The fan connects to GPIO pins 2 (5v) and 9 (ground). The GPS receiver connects to pins 4 (5v), 6 (ground), 8 (Tx), and 10 (Rx).
A suitable antenna connects to the SMA input on the preamp. The dipole antenna that comes with the RTL-SDR Blog V3 kit works good enough.

Finally, the 10,000mAH Power Bank slides firmly into the space at the bottom of the cube. It provides enough power for extended morning and evening chases. I also chose this power bank because it has an integrated USB-C power cord.

Looking at the bottom of the cube reveals the battery power level.
I have attached some gaffers tape to the bottom legs to keep it from sliding around.
The integrated USB-C cord from the power bank is the only cord that does not extend beyond the frame.

Usage

The software uses the WiFi hotspot on my phone for the data connection (should a data connection not be available the software can still function using offline maps). I then use a tablet to connect to a couple webpages that are hosted on the Pi. The first page is Chasemapper which is the primary display used during a chase. It displays the location of the radiosonde and your vehicle. It also provides range and bearing information so you can hopefully track down and recover the radiosonde.

The other webpage is the radiosonde_auto_rx status page. This shows the location of the radiosonde and a scan plot of the frequency range that is being searched. This page also allows you to look at and download historical track data.

Here is what the system looks like set up in my vehicle.

There is no radiosonde visible on the screen because it had stopped transmitting by the time I arrived on site (you can read about it here).