Over on the SDRplay blog Jon has posted about the STRATONAV experiment which makes use of the SDRplay RSP1 software defined radio. The STRATONAV experiment uses high altitude balloons to carry the RSP1 as well and a commercial portable receiver. The two receivers were configured to receive aircraft VOR navigation signals in order to test the effectiveness of VOR when used at extreme altitudes of up to 28 km. The VOR navigational data was then compared against GPS tracks, resulting in a measure of how well VOR worked at those altitudes.
VOR (aka VHF Omnidirectional Range) is a navigational beacon that is transmitted between 108 MHz and 117.95 MHz from a site usually at an airport. In the past we have posted about VOR a few times as it can also be decoded with an RTL-SDR, or used for passive doppler aircraft radar.
The results showed that VOR navigation does indeed continue to function at extreme altitudes, proving that it can be used as a back up navigation system for stratospheric platforms. They also note that VOR navigation could also be used as a primary navigation system on smaller stratospheric platforms due to its low cost and low complexity to implement.
Last month Jeff Deaton from "Edge of Space Sciences" (EOSS) presented a talk called "SDR Multi Balloon Tracking", where he discusses how EOSS are using RTL-SDR receivers to track their APRS high altitude balloons. EOSS is a Denver, Colorado based non-profit organization that promotes science and education by exploring frontiers in amateur radio and high altitude balloons. The talk overview reads:
Review of the software defined APRS system being used to track multiple balloon flights at EOSS. Overview of primary features like the graphical user interface and landing predictions as well as a discussion of the open source software used to power the system like GnuRadio, Dire Wolf, and Aprsc.
It appears that they've created some interesting software that they run on small portable computers that they take in chase vehicles. The software uses an RTL-SDR to receive the APRS signal from the high altitude balloons that they've launched, allowing them to track and predict the flight path, and ultimately recover the balloons and attached cameras.
RPiTX is software that enables the Raspberry Pi to transmit any modulated signal over a wide range of frequencies using just a single GPIO pin. However, the transmission contains multiple harmonics and thus requires sufficient filtering in order to transmit legally within the 2M ham band. To solve this ZR6AIC uses a 2M Raspberry Pi Hat kit which he designed and created that contains two low pass filters as well at the option for an additional power amplifier.
The rest of ZR5AIC's post explains how his HAB telemetry system combines the Raspberry Pi 3, RPiTX 2M Hat, RTL-SDR, a GPS unit, battery, temperature sensor and optional camera into a full HAB transmitting system. He also explains the software and terminal commands that he uses which allows him to transmit via RPiTX a CW beacon and GPS and temperature sensor APRS telemetry data with the Direwolf software. Full instructions on setting up the alsa-loopback audio routing is also provided.
David and Mark are building a 115 kbit/s FSK SSDV (slow scan digital video) data system for high altitude balloons. In their system, on the balloon transmit side they use a Raspberry Pi, Raspberry Pi camera and a RFM22B wireless transceiver modulator board to transmit the SSDV FSK signal. On the receive side they use an RTL-SDR dongle, low noise preamplifier and a GNU Radio program to demodulate the SSDV images. The first video below demonstrates the hardware and GNU Radio program and shows them receiving the SSDV signal. In the second video they demonstrate that the images can be received at low signal levels (-106dBm) as well, by heavily attenuating the signal.
While testing the RTL-SDR for use in this system they also measured the noise figure of an R820T RTL-SDR dongle. The noise figure at maximum gain comes out at around 5.6 dB. By adding a low noise amplifier they reduce the measured noise figure down to 2 dB.
Over on YouTube user kpappa has uploaded a video showing his reception of the J43VHF radio amateur stratosphere balloon with an RTL-SDR dongle and discone antenna. On the 10th of May radio amateurs in Greece launched a high altitude balloon. The balloon carried a transceiver payload which allowed amateurs to talk to each other via the balloon at a frequency of 144.200 MHz. The video shows good reception of the balloon and also shows it’s tracking via APRS.fi.
Around the world meteorological weather balloons are launched twice daily, and continuously transit weather telemetry to a ground station using something called a radiosonde. The RTL-SDR software defined radio combined with a decoding program can be used to intercept this telemetry, and display it on your own computer. You will be able to see real time graphs and data of air temperature, humidity, pressure as well as the location and height of the balloon as it makes it's ascent.
This tutorial is also applicable to other software defined radios such as the Funcube dongle, Airspy, HackRF, BladeRF or even hardware radios with discriminator taps, but the RTL-SDR is the cheapest option that will work.
In this example YouTube user Superphish shows a radiosonde being received and decoded using a RTL-SDR, SDRSharp and SondeMonitor.
Weather Balloon (Radiosonde) tracking with RTL SDR (RTL2832), Sondemonitor and SDR Sharp