Meteorological organisations across the world launch weather balloons on a regular basis as a part of their work in predicting whether or not it will rain on the weekend. Their payloads are called radiosondes, and these balloons deliver both telemetry and location data throughout their flightpath. Hobbyists around the globe have devoted time and effort to tracking and decoding these signals, and now it’s possible to do it all automatically, thanks to Radiosonde Auto RX.
The basis of the project is the RTL-SDR, everyone’s favourite low-cost software defined radio receiver. In this case, software is used to first hunt for potential radiosonde signals, before then decoding them and uploading the results to a variety of online services. Some of these are designed for simple tracking, while others are designed for live chase and recovery operations. Currently, the software only covers 3 varieties of radiosonde, but the team are eager to expand the project and have requested donations of other radiosondes for research purposes.
What do you get when you cross an ARM-based Linux PC and an RTL-SDR? Sounds like the start of a joke, but the answer is Outernet’s Dreamcatcher. It is a single PCB with an RTL-SDR software defined radio, an L-band LNA, and an Allwinner A13 processor with 512MB of RAM and a 1 GHz clock speed. The rtl-sdr site recently posted a good review of the $99 board.
We’ll let you read the review for yourself, but the conclusion was that despite some bugs, the board was no more expensive than pulling the parts together separately. On the other hand, if you uses, for example, a Raspberry Pi 3, you might expect more support and more performance.
Despite the L-band hardware, there is a bypass antenna jack that allows you to receive other frequencies. There’s also two SD slots, one to boot from and another for storage. Several pieces of software had trouble running on the somewhat sluggish CPU, although some software that is optimized for the particular processor used fared better. You can read the details in the review.
The board is interesting, although unless you have a special packaging problem, you are probably as well off to combine a Pi and a dongle, as we have seen so many times before. If you have more horsepower you can even make the Pi transmit, although we’d suggest some filtering if you were going to do that for real.
This week I was approached with a question. Why don’t passenger aircraft have emergency parachutes? Whole plane emergency parachutes are available for light aircraft, and have been used to great effect in many light aircraft engine failures and accidents.
But the truth is that while parachutes may be effective for light aircraft, they don’t scale. There are a series of great answers on Quora which run the numbers of the size a parachute would need to be for a full size passenger jet. I recommend reading the full thread, but suffice it to say a ballpark estimate would require a million square feet (92903 square meters) of material. This clearly isn’t very feasible, and the added weight and complexity would no doubt bring its own risks.
[Carl] just found a yet another use for the RTL-SDR. He’s been decoding Inmarsat STD-C EGC messages with it. Inmarsat is a British satellite telecommunications company. They provide communications all over the world to places that do not have a reliable terrestrial communications network. STD-C is a text message communications channel used mostly by maritime operators. This channel contains Enhanced Group Call (EGC) messages which include information such as search and rescue, coast guard, weather, and more.
Not much equipment is required for this, just the RTL-SDR dongle, an antenna, a computer, and the cables to hook them all up together. Once all of the gear was collected, [Carl] used an Android app called Satellite AR to locate his nearest Inmarsat satellite. Since these satellites are geostationary, he won’t have to move his antenna once it’s pointed in the right direction.
As far as antennas go, [Carl] recommends a dish or helix antenna. If you don’t want to fork over the money for something that fancy, he also explains how you can modify a $10 GPS antenna to work for this purpose. He admits that it’s not the best antenna for this, but it will get the job done. A typical GPS antenna will be tuned for 1575 MHz and will contain a band pass filter that prevents the antenna from picking up signals 1-2MHz away from that frequency.
To remove the filter, the plastic case must first be removed. Then a metal reflector needs to be removed from the bottom of the antenna using a soldering iron. The actual antenna circuit is hiding under the reflector. The filter is typically the largest component on the board. After desoldering, the IN and OUT pads are bridged together. The whole thing can then be put back together for use with this project.
Once everything was hooked up and the antenna was pointed in the right place, the audio output from the dongle was piped into the SDR# tuner software. After tuning to the correct frequency and setting all of the audio parameters, the audio was then decoded with another program called tdma-demo.exe. If everything is tuned just right, the software will be able to decode the audio signal and it will start to display messages. [Carl] posted some interesting examples including a couple of pirate warnings.
It hasn’t become a household term yet, but Software-Defined Radio (SDR) is a major player on the developing technology front. Whether you’re building products for mass consumption, or just playing around for fun, SDR is worth knowing something about and I’ll prove it to you.
[Balint] has a bit of history in dealing with software defined radios and cheap USB TV tuners turned into what would have been very expensive hardware a few years ago. Now [Balint] is finally posting a few really great GNU Radio tutorials, aimed at getting software defined radio beginners up and running with some of the coolest hardware around today.
[Balint] is well-known around these parts for being the first person to create a GNU Radio source block for the implausibly inexpensive USB TV tuners, allowing anyone with $20 and enough patience to wait for a package from China to listen in on everything from 22 to 2200 MHz. There’s a lot of interesting stuff happening in that band, including the ACARS messages between airliners and traffic control, something that allowed [Balint] to play air traffic controller with a minimal amount of hardware.
Right now the tutorials are geared towards the absolute beginner, starting at the beginning with getting GNU Radio up and running. From there the tutorials continue to receiving FM radio, and with a small hardware investment, even transmitting over multiple frequencies.
It’s not much of an understatement to say software defined radio is one of the most versatile and fun projects out there. [Balint] even demonstrated triggering restaurant pagers with a simple SDR project, a fun project that is sure to annoy his coworkers.
Using the Arduino embedded PWM controller in fast PWM mode and by manipulating the duty cycle, he actually managed to create a primitive form of amplitude modulation and was able to transfer a very simple audible signal at several frequencies up to 1.75GHz. Embedded after the break here is video of the system at work.
As a side note, did you know that during the solar storm of 1859 the EMI were so strong that the telegraph operators received several shocks? Pipelines maintenance systems also have to be aware of such events, that can lead sensors to provide inaccurate results.