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5 Chase Car Receiver Box

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Mark Jessop edited this page Feb 29, 2020 · 2 revisions

This page is a work in progress, and is an attempt to document construction & configuration of a 'black box' chase-car balloon tracking setup. This setup is intended to be loaned out to AREG club members interested in doing a Project Horus balloon or Radiosonde chase, but that don't have the equipment to do one.

Parts Required

Electronics

  • Raspberry Pi - suggest using a RPi 3B+, as the RPi 4 gets very hot.
  • MicroSD Card for RPi - 32GB will do. I recommend the 'Sandisk Ultra' series.
  • 12V -> 5V Power Supply. This needs to be RF quiet!
    • I highly recommend the Blue-Sea Systems USB supplies. They are not cheap, but they are well filtered, and I use them all over the place (SatNOGS station, car, etc...). They are available from Powerwerx, and are also stocked by many local marine shops.
  • RTLSDR (v3 model recommended)
  • (Optional) Preamplifier.
    • It's very possible to receive Horus Binary telemetry throughout a flight without any preamplifier. If you do want one, then something like the UpuTronics HabAmp is probably the best bet.
    • If you want to be able to do more than just Horus Binary telemetry (e.g. receive radiosondes), then you will either have to use a wide-band preamp (LNA4ALL or similar), or switch preamps when changing tasks.
  • USB GPS Receiver
    • For chasing you will need some kind of USB GPS receiver to show up on the ChaseMapper map. I would suggest a mag-mount type that you can put on your car roof.
    • There are a range of cheap USB GPS receivers available on eBay and AliExpress. Most of them work just fine. I'd suggest getting one with a uBlox chipset if possible, though anything that outputs standard NMEA sentences will work fine.
    • Example from AliExpress: https://www.aliexpress.com/item/32990134221.html
  • 3G/4G Modem
    • If you're in an area with good 3G/4G coverage, then you could configure the RPi to connect to a mobile phone hotspot.
    • If going into areas of poor coverage, then I would suggest using a dedicated 3G/4G modem, and an external antenna. It's hard to make recommendations on modems for this kind of thing, since the available hardware changes so often. You will likely need some kind of adaptor to be able to use an external antenna with these devices. Telstra currently (2020-02) sell a cheap USB-powered 4GX hotspot for only $40.

Antennas

  • 70cm Mag-Base Antenna

    • You don't need much to be able to receive Horus Binary telemetry. A simple 1/4-wave monopole will do. Even the stock RTLSDR antennas are known to work OK.
    • For a more robust commercial solution, the Diamond MR-77S is a nice mag-base antenna, and has been used on many Project Horus chases. Make sure to get the version that matches whatever bulkhead connector you are using!

  • 3G/4G Antenna

    • Jaycar sell mag-mount 3G/4G antennas that seem to work OK. (Any antenna outside the car is going to be an improvement over no external antenna).
    • In Australia, RFI make very good multi-band mobile 3G antennas. I use a RFI CD7194 on my car.

Hardware

  • Some kind of case to mount all of the above in!
    • You should ensure there is some airflow through the box otherwise the RPI might overheat, so look into cutting a hole in the side and mounting a fan. 12V PC case fans often work at 5V, and there's ample 5V available within the box.

Cabling & Adaptors

You're going to need RF cables for the following:

  • 3G/4G modem to bulkhead connector (??? to Bulkhead BNC or SMA)
  • (If using a preamp) RTLSDR to Preamp Input (SMA to SMA)
  • RTLSDR (or preamp) to bulkhead connector (SMA to Bulkhead BNC or SMA)

And the following other cables:

  • Bulkhead power input to 5V power supply input.
    • You probably want to have a 5A fuse inline on this cable.
  • USB-A (plug) to MicroUSB (plug) - to power RPi.
  • USB-A (plug) to USB-A (socket) - to power 3G/4G modem.
  • USB-A (plug) to USB-A (socket) - RPi to RTLSDR
  • USB-A (plug) to USB-A (socket - bulkhead mount) - Bulkhead socket to plug USB GPS into.

You will also probably need adaptors for the following:

  • 3G/4G antenna to bulkhead connector (often FME-to-SMA or FMA-to-BNC)
  • Any adapters required for your 70cm antenna.
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