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ATSC Transmitter
Broadcast television in the United States currently uses a set of standards developed by the Advanced Television Systems Committee. The digital ATSC standards replace the analog National Television System Committee (NTSC) standards for nearly all "major" broadcasters in the US and Canada.
In the typical deployment, ATSC broadcasts use 8VSB modulation in a 6 MHz channel to transmit a 19.39 Mbit/s MPEG Transport Stream, which contains a number of multiplexed video, audio, and data payloads.
To get to this point, you'll want to have your BladeRF connected to a USB 3.0 port, and be running a recent firmware and hosted FPGA image. You'll also need to have libbladeRF and gnuradio installed, generally by using the Quick Start instructions elsewhere in this wiki. I assume you'll be using Linux.
- Grab a transport stream from somewhere, such as: http://www.w6rz.net/advatsc.ts
(246 MB)
- Grab atsc-blade.py: https://gist.github.com/rtucker/8641650
- Make sure a "reasonable" UHF antenna is attached to your BladeRF's transmit port, and that physical channels 14 (470 to 476 MHz) and 15 (476 to 482 MHz) are unused in your area -- if not, adjust center_freq to land on some other channel.
- Turn on your DTV receiver and set it to broadcast channel 14 (or whatever you chose).
- Roll that beautiful bean footage:
python atsc-blade.py advatsc.ts
Transmitting pre-encoded content: advatsc.ts Using Volk machine: avx_64_mmx_orc gr-osmosdr v0.1.0-55-g80c4af4f (0.1.1git) gnuradio 3.7.1 built-in sink types: bladerf [bladeRF source] Using nuand LLC bladeRF #0 SN [redacted] FW v1.6.1 FPGA v0.0.2
Congratulations! You are now transmitting an ATSC signal! If it doesn't work straight away, check that you aren't getting a lot of overflow/underflow errors, and that LEDs 1 and 3 are *solid* on your BladeRF. Also, make sure your TV is set to tune to broadcast channel 14, not cable channel 14.
Press ctrl-C when finished.
What, you don't like Adventure Time?
If you have a video file that you want to try transmitting, install avconv (aka ffmpeg) and take a look at atsc-ts-converter.bash: https://gist.github.com/rtucker/8641882
This script specifies a video file (tbm_tdf_2.mp4) and saves it to a transport stream file (tbm_tdf_2.ts). It also puts a text overlay on it. Feel free to change TEXT, VIDEOFILE, and OUTFILE to suit your needs.
Note that the video just has to be in a format avconv can understand -- it will do the transcoding into something your TV should understand.
Be warned that MPEG Transport Streams are *big*:
-rw-r--r-- 1 rtucker rtucker 23839649 Dec 29 20:23 tbm_tdf_2.mp4 -rw-r--r-- 1 rtucker rtucker 792414924 Dec 29 20:54 tbm_tdf_2.ts
But once you have it generated, you can play it back, and it should work:
$ ./atsc-blade.py ~/Videos/tbm_atsc_test/tbm_tdf_2.ts Transmitting pre-encoded content: /home/rtucker/Videos/tbm_atsc_test/tbm_tdf_2.ts Using Volk machine: avx_64_mmx_orc gr-osmosdr v0.1.0-55-g80c4af4f (0.1.1git) gnuradio 3.7.1 built-in sink types: bladerf [bladeRF source] Using nuand LLC bladeRF #0 SN [redacted] FW v1.6.1 FPGA v0.0.2
(Yes, my television is an old GoldStar CRT with a cheap government-cheese DTV converter box. Stop laughing at me. I don't really watch television...)
For this, I'm going to turn one of my bicycle commutes into a music video. I mounted a crappy camera (we'll call it a GoCheap) to my bicycle and got a MJPEG video with a lot of gearshifting noise and heavy breathing on the audio track, so we'll replace that with some pleasant music.
- Grab atsc-ts-streamer.bash from my gist: https://gist.github.com/rtucker/8642061
- Update VIDEOFILE and AUDIOFILE to point at some video and audio
- In one terminal window, run
python atsc-blade.pywithout any arguments - In another terminal window, run
./atsc-ts-streamer.bash:
avconv version 0.8.9-6:0.8.9-0ubuntu0.13.10.1, Copyright (c) 2000-2013 the Libav developers
built on Nov 9 2013 19:09:46 with gcc 4.8.1
Input #0, avi, from '/home/rtucker/Videos/Bike Cam/2012-09-09-002-afternoon.AVI':
Duration: 00:16:20.15, start: 0.000000, bitrate: 9442 kb/s
Stream #0.0: Video: mjpeg, yuvj422p, 640x480, 30 tbr, 30 tbn, 30 tbc
Stream #0.1: Audio: pcm_mulaw, 8000 Hz, 1 channels, s16, 64 kb/s
[mp3 @ 0x19aa7c0] max_analyze_duration reached
Input #1, mp3, from '/home/rtucker/Music/Track N Field/Marathon/04 - Track N Field - Iso Maha.mp3':
Metadata:
album : Marathon
genre : Broken beat/Nu Jazz/Nu Soul
copyright : 2008 Nine2Five
TSRC : DEY470803172
title : Iso Maha
artist : TRACK N FIELD
album_artist : TRACK N FIELD
publisher : para-dise.biz
track : 4
date : 2008-08-01
Duration: 00:06:45.02, start: 0.000000, bitrate: 321 kb/s
Stream #1.0: Audio: mp3, 44100 Hz, stereo, s16, 320 kb/s
Incompatible pixel format 'yuvj422p' for codec 'mpeg2video', auto-selecting format 'yuv420p'
[buffer @ 0x196b740] w:640 h:480 pixfmt:yuvj422p
[scale @ 0x19fc020] w:640 h:480 fmt:yuvj422p -> w:1280 h:720 fmt:yuv420p flags:0x4
[mpegts @ 0x19aee00] muxrate 19393000, pcr every 257 pkts, sdt every 6447, pat/pmt every 1289 pkts
Output #0, mpegts, to 'udp://127.0.0.1:1234?pkt_size=188&buffer_size=65535':
Metadata:
service_name : udp://127.0.0.1:1234?pkt_size=188&buffer_size=65535
service_provider: BladeRF ATSC Demo
encoder : Lavf53.21.1
Stream #0.0: Video: mpeg2video, yuv420p, 1280x720, q=2-31, 2000 kb/s, 90k tbn, 30 tbc
Stream #0.1: Audio: ac3, 48000 Hz, stereo, s16, 384 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (mjpeg -> mpeg2video)
Stream #1:0 -> #0:1 (mp3 -> ac3_fixed)
Press ctrl-c to stop encoding
frame= 2172 fps= 30 q=31.0 Lsize= 171281kB time=72.37 bitrate=19389.3kbits/s
And boom! You should see it on your television, with your chosen music on the audio channel.
You might notice the signal breaks up more than you'd like. The transcoding and multiplexing are being done in real time and that is somewhat stressful. Ways to improve this are welcome.
So all that was boring. Why don't we try something more exciting? My laptop has a webcam.
Copy the atsc-ts-streamer.bash script to a machine on the same ethernet segment as the machine running atsc-blade.py (or maybe the same machine, if you have a webcam!) and set the following:
VIDEOFILE="-f video4linux2 -r 30 -s vga -i /dev/video0" AUDIOFILE="-i http://audioplayer.wunderground.com:80/dampier/rochester.mp3" # or some other suitable streaming audio content OUTFILE="udp://192.168.1.194:1234?pkt_size=188&buffer_size=65535" # replace 192.168.1.194 as required
Start up ```atsc-blade.py``` with no arguments, and then, on your webcam machine, start ```atsc-ts-streamer.bash```. If all goes well, holy crow!
The stream tends to be somewhat more unstable in this case, perhaps due to network packet loss, perhaps due to the constraints of real-time video encoding. Research into improving this is welcome.
Props to argilo for atsc-blade.py and drmpeg for the advatsc.ts transport stream, both of which provided a foundation for making this a thing.
Also, to take the next step, try implementing a DVB-T transmitter and making contacts over the air! (Yes, you can use the low-cost RTL-SDR USB fob as a television receiver.) http://www.irrational.net/2014/03/02/digital-atv/
To save cycles on his host machine, modus_tollens developed an FPGA image for ATSC transmission that offloads the modulation, pilot insertion, filtering, and shift to baseband. The host simply needs to provide the 4-bt ATSC symbols.
This FPGA can be built using the atsc_tx revision with the FPGA build_bladerf.sh script.
As detailed in this forum post, drmpeg leveraged this FPGA bitstream and added an FPGA symbol mapper block to allow an ATSC stream to be written directly to an Osmocom Sink block. This allows one to utilize the ATSC TX FPGA image in conjunction with GNU Radio.