What is Digital Video Broadcasting?
How can I get involved in ATV in the St Louis area?
SLATS (St Louis Amateur Television Society) has a Wednesday morning net (10 a.m. local St Louis time) that welcomes check-ins on 144.34 MHz simplex. ATV stations also use 144.34 MHz FM as a “talk back” frequency to converse with other stations transmitting on ATV and is monitored by the ATV community. Future club meetings are being planned now. Check the SLATS web sites for time and location.
What distance can I expect to have with my digital ATV station?
Depending upon your antenna configuration (usually a single 70cm Yagi vertically polarized with operating power around 10 watts average), paths to the repeater are possible up to 15 miles. Longer distances are possible but may require higher gain and antenna height. The WØATN repeater is located in NW St Louis County near I-70 and I-270.
Why is Digital Video Broadcast-Terrestrial (DVB-T) being used as the Digital ATV standard on the WØATN repeater?
Although DVB-T is not used commercially in the United States, this European standard has been adopted by ATVers in the United States primarily because inexpensive commercial gear (Hi Des) has been readily available for amateur use. Also, the HiDes transmitters’ bandwidth can be set to transmit and receive 4 MHz width using 16QAM signals making it more robust than the US standard. DVB-T provides High-Definition (HD) 1920 by 1080p and full-motion (30 FPS) plus efficient spectrum use along with increased realized gain performance when compared to a 6 MHz-wide digital ATV signal.
What makes general ATV activities or activities on the ATV repeater any better than streaming video or Skype?
Because this mode is not as Plug-and-Play as some other modes of amateur radio, the availability of a known-good signal from the WØATN repeater becomes essential in setting up an effective digital ATV station. And DVB-T users will find the quality of the picture is better than available with most Skype connections.
What will I see and hear if I were to get a DVB-T receiver (Such as a HiDes HV-110) and be within range of the WØATN ATV Repeater?
In addition to receiving video from stations in the metro area, you will be able to receive an HD full-motion continuous loop video with audio that includes an ID and current repeater and user information. WØATN’s transmitter is turned on and the ID played with a TouchTone command by the repeater user. In addition to the video/audio stream, other outputs are available including an on-site video camera and a live NASA stream. The default output is from the repeater’s receiver. A watch-dog timer monitor’s usage.
How much does a HiDes HV110 DVB-T Receiver cost?
Currently, they are listed at $125. During the near year holidays, the receiver is normally on sale for $99.00. Visit HIDes web site at www.hides.com.tw for current pricing.
Can I use any commercial DVB-T receiver?
Currently, there are some other options, but the receiver MUST be able to receive narrowband (4 MHz wide) DVB-T signals. Most commercial (HIDes being an exception) USB dongles and set-top box receivers are not configured for the narrow bandwidth (< 6MHz) amateurs here in the U.S. use with the DVB-T standard.
I have an old PC Electronics 70cm ATV analog transceiver. Can it still be used?
No, with the closure of the KDØLO analog repeater, the WØATN was designed as the replacement for standard and high definition digital ATV only.
How well will I see the DVB-T video?
The DVB-T signal will be received in the same HD quality video/audio as received from a commercial over-the-air (OTA) television stations. This allows sharing a computer screen with the receiving station, an HD video camera and another video/audio content consistent with FCC regulations.
What are all those Acronyms?
Acronyms for DATV
BER – Bit error ratio. Ratio between the number of bits in error and total number transmitted
B-frame – Bi-Directional predicted frame coded with respect to I and P frames
CAT – Conditional Access Table – A Transport Stream table that lists the PID values.
DVB-T – Digital Video Broadcasting – Terrestrial – European Television Standard
EPG – Electronic Program Guide – Note: not used in DVB-T
ES – Elementary Stream Generated by the video or audio encoder
FEC – Reed Solomon RS(204, 188, T=8) Convolutional Interleaving follows RS Manipulates the data prior to the transmission before any errors are introduced.
GOP – Group of Pictures. Term used in MPEG compression.
H.264 – Advanced codec for video compression, open, licensed industry standard
I-frame – Intra frame. Coded w/respect to no other frames but themselves
ISI – Inter-symbol interference causing overlapping of successive symbols
MER – Modulation Error Ratio 40 dB is good 34dB is poor, DATV 25 is pretty good
MPEG – Moving pictures expert group that sets standards for video and audio
OFDM – Orthogonal frequency division multiplex. Used by DVB to transmit data.
OSD – On screen display. Graphics displays of menus and images on the TV screen
Orthogonality – Complete independence of two or more signals (as in OFDM).
P-frame – Predicted frame coded w/respect to I and P frames that preceded them
PAS – Program association section. These make up the PSI tables in DVB.
PAT – Program Allocation Table – Always present and carried by the packets PID
PCR – Program Clock Reference
PES– Packetized Elementary Streams – Program stream may have one or more PES
PID – Packet Identifier PES ID number. Defines a particular elementary stream.
PILOT = Carriers used for implementation correction processes at the receiver.
PMT – Program Map Table – One for each program present in the multiplex
PSI – Program Specific Information – Defined by tables from the PES streams
PTS – Presentation Time Stamp – Sync audio and video
PU – Presentation Units
Puncturing – A method to reduce the amount of redundant data.
QPSK – Quadrature phase shift keying. A modulation technique using 4 different phases to encode information.
QAM – Input symbols converted into 2 signals – I (in-phase) and Q (quadrature) then to D/A. The output represents constellation and modulates the TX Modulator using IFFT which converts data from the time to freq domain
QEF = Quasi error free. Comm channel that limits errors to around 1 in 1010 bits Transmitted. DBV-T requires a QEF channel = reason for FEC.
RS – Reed-Solomon. BTL scientists developed error correction techniques for data
RST – Running status table. A DVB table allows updates of timing status.
S/N or SNR = Signal to noise ratio in dB. Higher the better signal received.
TP = Transport packets used to transmit Elementary Streams by splitting them up into packets.
TPS – Transmission Parameter Signaling Parameters of the transmission scheme
