Transmitting DATV with a just a Raspberry Pi

All the way back in April 2014 we first posted about how the Raspberry Pi was able to transmit FM by cleverly modulating one of it’s GPIO pins. Later in October 2015 F5OEO expanded this idea and created software that allowed the Raspberry Pi to transmit not only FM, but also AM, SSB, SSTV and FSQ. Soon after some filter shields such as the QRPi were released to try and cut down on the spurious emissions caused by transmitting using this method.

Now F5OEO has once again taken this method a step forward and has created software capable of allowing the Raspberry Pi to transmit Digital Amateur TV (DATV). The software is called Rpidatv, and can be downloaded from https://github.com/F5OEO/rpidatv. It can be run from the command line, or via a touch graphical interface if you have a touchscreen LCD screen. DATV is a DVB-S broadcast and can be decoded with an RTL-SDR by using the leandvb software which is bundled together with the Rapidatv software. Previously we’d posted about how the International Space Station intends to one day transmit DATV and that it can be decoded with an RTL-SDR.

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.

A DATV transmission received from a Raspberry Pi transmitter.
A DATV transmission received from a Raspberry Pi transmitter.
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Comparing the FunCube Dongle Pro+, Airspy/SpyVerter and SDRplay on Shortwave

Over on YouTube user London Shortwave has uploaded a video showing a comparison of the FunCube Dongle Pro+, Airspy with SpyVerter upconverter and SDRplay on shortwave reception. The Funcube, Airspy and SDRplay are all $150 – $250 USD software defined radios that have much higher performance compared to the RTL-SDR.

In the video he tests the reception of Radio New Zealand International (RNZI) at 9400 kHz using a 6m copper wire dipole and 9:1 matching balun raised 2m off the ground. He did not use any external antenna preselectors. The RNZI station is weak and appears to be almost blocked by a stronger station so reception of the station is difficult.

In his results it appears that the FunCube and Airspy/SpyVerter are able to clearly receive the RNZI station, but the SDRplay has trouble with images of other stations mixing into the signal.

If you are interested in a comparison of the Airspy, SDRplay and HackRF we previously did our own review here.

Portable SDR Shootout Part 1

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Finding Cheap Pre-Designed PCBs for SDR Projects

Recently RTL-SDR.com reader Neil KM4PHK wrote in to us to let us know that he’s been having a good time searching for SDR related PCB’s over on OSH Park. OSH Park is a company that allows you to upload and share a PCB, and then have it cheaply printed and sent to you for construction.

Some useful RTL-SDR related PCBs we found searching through their shared projects include PCB’s for a SAW filter, a PSA4-5043+ based LNA, an MGA-53543 based LNA, a lowpass or bandpass filter, an FM trap, an ADS-B filter with LNA and a bias tee. More projects can be found by searching the shared projects page for strings like “SDR, LNA, Filter, Bias Tee, ADS-B”. Neil also writes that although some projects don’t have instructions on their OSH Park page, usually searching Google will reveal them.

An example PCB for an LNA that can be found on OSH Park.
An example PCB for an LNA that can be found on OSH Park.
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Setting up a Raspberry Pi Based AIS Receiver with an RTL-SDR

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.

$50 Raspberry Pi AIS-Receiver - How to

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Partial Discharge Detection using an RTL-SDR

Partial discharge is the situation in which electricity arcs through an insulating dielectric material when high voltages above the rated voltages for the insulator are applied. Continued partial discharge can cause the insulator to eventually be destroyed and fail, potentially causing catastrophic failure.

Recently a technical academic paper by H Mohamed et al. was released and titled “Partial Discharge Detection Using Low Cost RTL-SDR Model for Wideband Spectrum Sensing”. In the paper they investigate using the RTL-SDR as a low cost means for partial discharge detection in equipment such as power generators, motors, gas insulated switchgear, and power grid equipment for the purpose of improving the future electrical smart grid.

Partial discharge can be detected using a spectrum analyzer to monitor the spectrum for noise signatures associated with a discharge. Using a program written in MATLAB to make the RTL-SDR act as a spectrum analyser they show that the measured spectrum can be used to detect when partial discharge is occurring and that the results are similar to a more expensive spectrum analyzer.

Lab set up for using an RTL-SDR to detect partial discharge.
Lab set up for using an RTL-SDR to detect partial discharge.
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Review: FlightAware ADS-B RTL-SDR + LNA Positioning

Recently FlightAware released a new RTL-SDR dongle sold at zero profit at $16.95 USD. It’s main feature is that it comes with an ADS-B optimized low noise amplifier (LNA) built directly into the dongle. FlightAware.com is a flight tracking service that aims to track aircraft via many volunteer ADS-B contributors around the world who use low cost receivers such as the RTL-SDR. In this post we will review their new dongle and hopefully at the same time provide some basic insights to LNA positioning theory to show in what situations this dongle will work well.

FlightAware Dongle Outside
FlightAware Dongle Outside

A good LNA has a low noise figure and a high IIP3 value. Here is what these things mean.

Continue reading →

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AISRec Updated to Version 2.1

AISRec is an RTL-SDR (and now Airspy) compatible AIS (automatic identification system) dual channel decoder. AIS is an acronym for Automatic Identification System and is a system used by ships to broadcast position and vessel information. By monitoring AIS transmissions with the RTL-SDR we can build a boat radar system.

Last time we tried AISRec we found its performance to be very good, with it decoding more messages than other software we tried. The new version includes the following updates:

  • Added auto detection of devices when devices are plugged in.
  • Added the support for airspy. Allow selection of devices by serial number for rtlsdr dongles.
  • Added AISRec core 3.0. The new core is 2x faster than AISRec core 2.0.
  • Added one embedded multi-user TCP server. Any client works with AISRec should implement auto reconnection.
  • Added auto display of local IP for the TCP server.
  • Added one output to one serial port.
  • Added interactive changes of gain parameters for devices.
  • A few changes on GUI.
  • Added an icon for GUI. Users should reset the windows icon buffer to allow the display of the new icon.

In addition, while AISRec hopes to be commercial software one day, at the moment they are currently offering free registration. See their FAQ for information on registering for free.

AISRec running with OpenCPN.
AISRec running with OpenCPN.
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Receiving Differential GPS Beacons with a HackRF

Differential GPS (DGPS) are signals that exist between 285 – 325 kHz and are used to enhance the accuracy of GPS receivers. The system can improve GPS accuracy from 15m down to 10cm in some cases. It works using a network of ground stations at a very accurate known location that continuously measure the GPS error they receive. They then broadcast this error to DGPS capable receivers. The receiver can then use this error knowledge to correct their own readings.

With an VLF capable radio these DGPS beacons can be received and decoded on your PC. Over on swling.com guest poster Mario has submitted a post showing that these DGPS beacons can be received with a HackRF SDR and the MultiPSK software. The HackRF is a $299 SDR that can tune down to VLF (at reduced sensitivity). We note that the same or better results could also be achieved with a HackRF or RTL-SDR with upconverter.

DGPS received with a HackRF
DGPS received with a HackRF
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