The Odroid C2 is a $40 USD single board computer with a 1.5 GHz ARM-A53 quad core CPU and 2 GB of RAM. Compared to a Raspberry Pi 3 it is more powerful and costs almost the same. YouTube uploader radio innovation recently wrote into us and wanted to share his video showing SDR-J decoding DAB+ smoothly on his Odroid C2. It seems that SDR-J works perfectly and only uses a small amount of CPU.
DAB stands for Digital Audio Broadcast and is a replacement/alternative to standard broadcast FM stations. SDR-J is a software suite that includes a DAB decoder for the RTL-SDR. It is compatible with Windows, Linux and the Raspberry Pi (and evidently also the Odroid C2). Over on their website they also provide a ready to go Raspberry Pi 2 image, and they write that it should perform well on the Rpi2 platform as well.
A radio repeater is usually a radio tower that receives weak signals from handheld, desktop or other radio, and rebroadcasts the same signal at a higher power over a wide area at a different frequency. This allows communications to be extended over a much greater area.
Rpitx is software for the Raspberry Pi which we have featured on this blog several times in the past. We’ve also seen the qtcsdr software which also uses Rpitx and an RTL-SDR to create a transceiver. Rpitx allows the Raspberry Pi to transmit radio signals without the need for any transmitting radio hardware at all. It works by modulating signals onto a General Purpose I/O (GPIO) pin on the Raspberry Pi. If the GPIO pin is modulated in just the right way, FM/AM/SSB or other signal modulation approximations can be created at a specified frequency. The signal is however not clean, as this type of modulation generates many harmonics which could be dangerous if amplified. If you use Rpitx, always use appropriate filtering hardware.
ZR6AIC’s post goes into detail about how to install and set up the required software onto the Raspberry Pi and how to set up the script to piece all the programs together into a repeater. He’s also uploaded a video demonstrating the system in action on YouTube.
A few days ago we posted about the release of Rpidatv, a program that allows a Rapberry Pi to transmit DATV without the need for any additional hardware. DATV stands for Digital Amateur TV, and can be received with an RTL-SDR using a program called leandvb.
Over on YouTube, the programmer of Rpidatv (Evariste F5OEO) has uploaded a video that shows a Rpidatv + leandvb system in action. The video demonstrates the touch screen GUI which can be used if a touch capable LCD screen is connected to the Raspberry Pi. It also shows the whole system in action with a video being transmitted from the Raspberry Pi camera to a Linux PC with an RTL-SDR running leandvb.
Another video uploaded to YouTube by Qyonek also shows Rpidatv + leandvb in action.
F5OEO writes that the software is capable of generating a symbol rate from 64k symbols to 1M symbols, which is enough to transmit one video with good H264 encoded quality. He also writes that using a low symbol rate may be useful for long distance transmissions as the signal will take up a smaller bandwidth. For example a 250K symbol transmission would only need 300kHz of bandwidth. He writes that this type of transmission could easily be used in the ISM band to replace WiFi video for FPV, but that at the moment video latency is about 1 – 2 seconds and is still being improved.
Once again we remind you that if you intend to transmit using these methods where a GPIO pin is modulated, then you MUST use a bandpass filter at the frequency you are transmitting at, and that you must be licensed to transmit on those frequencies.
Over on YouTube user Tobias Härling has uploaded a video showing how he used a Raspberry Pi and RTL-SDR dongle to set up an AIS receiver. AIS stands for Automatic Identification System and is a radio system similar to ADS-B which allows you to create a radar-like system for boats. For Windows we have a tutorial on AIS reception here.
In his setup he uses rtl_ais and the kplex software and shows how to install everything from scratch. He also shows how to set the system up so that decoding automatically starts up and begins outputing NMEA data through the network when the Raspberry Pi is powered on. This way an a device like an iPad could be used to run OpenCPN to view the plotted ships.
Over on his blog rtlsdr4everyone author Akos has recently uploaded three new posts. The first post is about the Raspberry Pi minicomputer and the post discusses the merits of using the Raspberry Pi with an RTL-SDR dongle. The second post provides information to help people new to RTL-SDR choose their first dongle, and weighs up options between dongles that cost $10, $20, $25, $35 and $50 dollars. Finally, the third post compares two dongles on HF performance.
PiTX works by modulating the GPIO pins on the Pi in such a way that it is able to produce FM modulation. The major problem with using this method of producing radio is that it creates large amounts of harmonics and interference outside of the intended transmit frequency. Interference like this is illegal and could potentially disrupt life critical radio systems such as emergency services, cellphones and air traffic control.
In order to cleanly transmit with PiTX an output RF filter should be used. Recently, the team over at TAPR.org have released a 20M WSPR TX filter shield. WSPR is pronounced “Whisper” and is short for “Weak Signal Propagation Reporter Network“. It is a type of amateur radio signal that can be broadcast and received around the world by using very low transmit power. Radio amateurs use it to see how far their signal can travel when using very low power (QRP) and to investigate signal propagation conditions.
Docker is a Linux based platform which allows you to build and deploy complex applications into a self contained “container” package that contains all the needed applications and dependencies. The container is completely preconfigured to just work as soon as you install the application without the need for any extra configuration.