Tagged: digital amateur television

Videos Showing Rpidatv in action

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.

rpidatv with leandvb

rpidatv with leandvb

Another video uploaded to YouTube by Qyonek also shows Rpidatv + leandvb in action.

Testy rpidatv + leandvb

Testy rpidatv + leandvb

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.

Receiving Digital Amateur TV from the ISS with an RTL-SDR

The international space station (ISS) is currently testing transmission of a DVB-S digital video signal. At the moment only a blank test pattern is transmitted, but one day they hope to be able to transmit live video properly for the purposes of making live contact with astronauts, and possibly to stream video of scientific experiments, extravehicular activities, docking operations, or simply live views of the Earth from space.

Over at www.pabr.org the author Pabr has been experimenting with using an RTL-SDR dongle for the reception of these digital amateur TV (DATV) signals. Over on Reddit he also posted some extra information about his work:

I have been able to receive DVB-S broadcasts from the ISS (known as HamVideo or HamTV) with a high-gain 2.4 GHz WiFi antenna ($50), a custom downconverter ($65), a R820T2 dongle, and a software demodulator (Edmund Tse’s gr-dvb). I used to think this could only be done with much more expensive SDR hardware.

It is commonly known that rtl-sdr dongles do not have enough bandwidth to capture mainstream satellite TV broadcasts, but the ISS happens to transmit DVB-S at only 2Msymbols/s in QPSK with FEC=1/2, which translates to 2 MHz of RF bandwidth (2.7 MHz including roll-off).

Before anyone gets too excited I should mention that:

  • This was done during a favourable pass of the ISS (elevation 85°)
  • With a fixed antenna, only a few seconds worth of signal can be captured
  • Demodulation is not real-time (on my low-end PC)
  • Currently the ISS only transmits a blank test pattern.

I now believe the BoM will be less than $50 by the time the ISS begins broadcasting interesting stuff on that channel.

Pabr uses a 2.4 GHz parabolic WiFi antenna to receive the signal. He writes that ideally a motorized antenna tracker would be used with this antenna to track the ISS through the sky. Also since the DATV signal is transmitted at around 2.4 GHz, a downconverter is required to convert the received frequency into one that is receivable with the RTL-SDR. The DATV decoder is available on Linux and requires GNU Radio.

Receiving DATV from the ISS
Receiving DATV from the ISS with an RTL-SDR

Transmitting DATV DVB-S Video with the HackRF Blue

Simon (G0FCU) has been using his HackRF Blue to transmit DVB-S video captured from his video camcorder. In the ham radio hobby there is something called digital amateur television (DATV) in which amateurs transmit digital video over radio to repeaters. Simon writes that in the UK DATV is usually transmitted at above 1.2 GHz and in the DVB-S format, which is the same format used by some satellite TV services.

Although there are dedicated DATV radios, Simon decided that he wanted to use the HackRF Blue as the radio for transmitting his own DATV signals. To do this he uses the software dvgrab to grab the video stream from the camera, then passes it to ffmpeg to compress the raw video into MPEG-2 and then uses a GNU Radio program called gr-dvbs to use the HackRF to transmit the DVB-S stream at 1000 MHz.

To test that his signal was transmitting correctly, Simon then used a standard DVB-S satellite TV with the LNB bypassed. 

Previously we also posted about using a BladeRF for transmitting DATV DVB-T signals.

What the DVB-S output signal looks like on another HackRF.
What the DATV DVB-S output signal looks like on another HackRF.