ATV
ATV, or Amateur Television is the use of the Amateur Radio frequency bands to transmit video. Slow-Scan TV is used on HF/VHF but this page deals with Fast-Scan TV used on UHF/SHF, either with Analogue PAL FM transmitters, or more recently with Digital DVB transmitters (as Digital ATV or DATV).
DATV
I am interested in Digital ATV as it combines my interests of Computer processing with Amateur Radio and Electronics! There is also a vast improvement that can be obtained by moving to more modern codecs over those currently in use by the Amateur Community.
DigiLite
I am in the process of building a DigiLite DVB Transmitter, this uses a Hauppage TV Card in MS Windows to provide an MPEG-2 video stream that is then processed into a DVB-S stream (Transport stream + FEC) before being output on a USB interface to drive a QPSK transmitter. The end result is a Digital TV signal can can be decoded by standard consumer (DVB-S) satellite receiver and is surprisingly robust.
I have heard that Brian, G4EWJ, is implementing a UDP input option to Digilite. This would enable streaming the video stream from Open Broadcast Encoder (discussed below), which could be run on a seperate computer. I look forward to this possibility as it would open up a great amount of flexibility for the setup.
Linux software
I have been searching for a Linux solution to a transmitter, particularly the use of a software encoder to allow the use of different codecs (MPEG-4, VP8, H.264). The original Poor Man's DATV (PMDATV) system built by M0DTS (Website) used the same Hauppage Card to provide Hardware encoding, and used a concatenation of OpenCaster and gbDVB for the relevant processing of the stream. This solution, albeit functional, was difficult to setup and unreliable.
My search for suitable software led me to Open Broadcast Encoder. Intended for Commercial Internet Broadcast stations, this software is designed to perform realtime encoding and streaming of video using Transport Streams.
The author has listed in the Wiki the possibility of adding Software DVB Encoding. If implemented, this actively maintained, funded and professional-class software would be able to perform all the functions from the encoding of input video to the output of raw data for I/Q modulation. All of this from a piece of free, open-source software running on a free, open-source OS! I am aware that the CPU requirements for realtime video encoding are massive, but there are ways to overcome this.
As of the moment the software is in Beta stage, I am waiting for the next beta release before trying the program out. The development can be followed on the github repository here.
Raspberry Pi
The amazing folks over at the Raspberry Pi Foundation have got a camera module connected to the Pi and capturing pictures through the GPU. This camera is 14 MegaPixels and capable of HD video. The really exciting part though is the fact that the Broadcom GPU in the Raspberry Pi contains a 1080p30 Hardware H.264 encoder, if this encoder could be controlled in a similar way to the Hauppage TV card (set to a low bitrate, hard-CBR stream), then the RPi could be an ultra-compact solution for DVB-S2/H.264 video capture + encoding. A USB connected Digilite-style LO+Modulator would be all the extra hardware required for DVB-S2 RF.
Misc
I have recently found a project by Fabrice Bellard, a major FFMPEG developer, that successfully transmitted VHF DVB-T from the VGA output of a graphics card here. Unfortunately he states that "the source code won't be available any time soon" and with no update since 2005 there is nothing to aid reproduction of this method.
USB Live2 Video Capture Card
This card is usable in Linux with Kernel 2.6.37 and above. For systems on older kernels you will need to build the driver from the v4l source code. You can find my instructions on doing this here, along with the no-blue-screen patch.
I use this capture card to view the output of TV receivers, viewing low SNR pictures in Linux requires a kernel driver patch to remove the Blue Screen, otherwise present when the card is unable to get SYNC lock. You can find this patch here.
Local Repeater - GB3IV
My local 23cm ATV repeater on the Isle Of Wight, mostly analogue but increasingly often digital operation. The official website is scartclub.co.uk/gb3iv.
- Live stream: batc.tv
- Output: 1316 Mhz FM PAL
- Co-located with GB3IW 70cm FM voice repeater on 433.225 Mhz (TX +1.6Mhz).
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