DATV / Digital Amateur Television Primer

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Introduction

Work on this page began a few days ago. Please help to fill in the gaps or provide references/images if you can. Please send any contributions/corrections to:  

 

The aim of this web page is to document some of the information that I have recently gathered, providing a single point of reference for newcomers seeking a basic introduction to the digital aspects of the ATV hobby. I don't hold any claim on technical authority, the sole purpose of this web page is to act as a single, convenient, repository for DATV related research. Please contribute corrections or new material as you see fit.

Much of this document is written from a European perspective. Please drop me a note if you can help to explain the DATV modes that are in use in your part of the world.


DATV Primer


What is DATV?

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Why Use DATV?

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Which bands can I use for DATV?

70 cm, 436 MHz Preferred

The narrow bandwidth of DATV, relative to analogue ATV, facilitates the use of full colour ATV in the UHF 70 cm band. UK Stations are transmitting 2 MHz bandwidth DATV around 436 and 437 MHz. QPSK and GMSK modes are in use although GMSK receivers are not generally available at this time.

23 cm, 1285 MHz Preferred

After the IARU region 1 conference 2005 in Davos, the 1.3 GHz bandplan now shows the 1272 to 1291 MHz segment usage to include DATV. It has been proposed that DATV activity be concentrated between 1281 and 1289 MHz with the centre of activity on 1285 MHz. This allocation has been chosen to allow 8 MHz bandwidth signals to be exchanged without impact on EME and SSB segments.

13 cm and Above

The availability of spectrum for DATV above from 13 cm upwards is generous and it is anticipated that these bands will be used to provide broader bandwidth, higher symbol rate, DATV transmissions with multiplexed signals containing many video and data signal sources. A typical application for multiplexed DATV video is to allow many repeater inputs to be rebroadcast simultaneously on one RF carrier.


What modes can I use for DATV?

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What is the difference between the DVB modes such as DVB-S and DVB-T?

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What do parameters like Symbol Rate and FEC mean?

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Typical broadcast implementation of DVB technology

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Typical amateur implementation of DATV technology

Click the thumbnail image below to view a high level block diagram of a typical Digital Amateur TV station. This configuration is based upon the SR-Systems modules.


Where can I see DATV today?

In the UK many of the Home Counties Repeater Group systems support DATV. GB3HV was the first UK repeater to be DVB-S DATV enabled using ex-broadcast hardware. If you are not within range of the Home Counties Repeaters you can still observe proceedings in real-time by using the GB3HV Streaming facility.

Active UK DATV Repeaters

Callsign RX Frequency TX Frequency Symbol Video Audio FEC Mode Comments
GB3HV 1252MHz 1308MHz TX 4M S/sec     1/2 QPSK Can receive DATV upon command. See GB3HV web site.
GB3KM 2328-2388MHz 2440MHz           No details of digital mode on web site. Can you help?
GB3RV 10425MHz 10065MHz TX 6M S/sec     1/2 QPSK Source: G8DHE's web page
GB3SQ 1280MHz Proposed 3cm 1311MHz TX 4M S/sec     1/2 QPSK Proposed Repeater: See G8AJN's site and BATG's site for details. Repeater has been used for digital tests during 2007.
GB3TZ 2388MHz 2326MHz           No web site to confirm digital access details or frequencies

Please contact G7LWT if you have exact symbol rates and details for DATV access to the repeaters listed above or if any additional repeaters should be listed.

Simplex Contacts on 70 cm

Most UK simplex activity seems to be on 70 cm at the moment. The table below shows the preferred settings:

Frequency 436.0 MHz
Symbol Rate 2 M S/sec
Video bit rate ~1.5 Mbit/s
1 Audio 64 K bits / sec
FEC 3/4 or 1/2
Mode DVB-S QPSK (not C-OFDM)
RF Bandwidth 2 MHz (435 to 437 MHz only)
Talkback 144.750 MHz FM

Simplex Contacts on 23 cm

 The table below shows the preferred settings for 23 cm simplex working:

Frequency 1285 MHz
Symbol Rate 4 M S/sec
FEC 1/2
Mode DVB-S QPSK
RF Bandwidth 8 MHz (1281 to 1289 MHz only)
Talkback 144.750 MHz FM

 


How can I get on air with DATV?

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How much of my existing ATV equipment can I use for DATV?

Although many analogue ATV station components can be reused with DATV, certain components either have to be swapped out or used in subtly different ways.

The following analogue ATV items can usually be reused in a DATV station:

The following analogue ATV components must be used carefully or replaced in a DATV station:


How can I scan the band for DATV signals?

Whilst it's not as easy as spinning the tuning dial on a rotary tune analogue satellite receiver, there are technical solutions to the basic need to tune the band looking for video signals. Many of the cheaper DVB receivers, such as those from Fortec Star, include a facility to rapidly band scan for new DVB satellite channels, automatically identifying symbol rates and other parameters. If you are looking for a more interactive approach to finding DX signals you may wish to consider modifying a satellite receiver to make a spectrum analyser, with spectrum surveillance capability, via a host PC.

Reproduced with kind permission. Copyright (c) Fred Bruenjes - moonglow.net

Screen Shot from BLSA Project. Timed scan: 500MHz of spectrum scanned repeatedly for six hours shows DVB newsfeeds come and go. Frequency is top to bottom and the passage of time is left to right.


How do I grade a DATV Contact?

Many aspects of the well established "P rating" system for ATV contacts are no longer relevant to grading a digital ATV contact. The following values have been proposed for a "D rating" system to be used when grading DATV reception:

P Rating  Analogue Meaning S/N Signal Strength D Rating Digital Meaning BER
P0 Trace of a picture barely visible, if at all. <3 db  <5 uV D0 Station ident received but no picture resolved  
P1 Picture visible but only large objects. 3-8 dB  5-15 uV D1 Severely corrupted picture freezes for long periods  
P2 Picture is visible but very noisy. 8-20 dB 15-50 uV D2 More Mosaics than clear picture,  
P3 More picture detail than noise. 20-35 dB 50-200 uV D3 Picture regularly turns into mosaics and/or audio drops  
P4 Good picture detail, slight noise. 35-45 dB 200-1000 uV D4 Infrequent audio and/or picture corruption  
P5 Perfect picture, no noise. >45 dB > 1000 uV D5 Perfect picture and sound  

Additional notes to explain the significance of Bit Error Rates etc will go here. Sample screen shots to be captured and incorporated into primer.


What does the future hold for DATV?

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Further Reading and Source Material for the DATV Primer

Once you have exhausted all the information in this DATV Primer you will find more related reading by following the links below:

 

DATV on the Web

    AGAF DATV Pages (DE/EN/FR) Hardware project in collaboration with the University of Wuppertal

    ATV Projects Web site by Brian Kelly GW6BWX

    Bourenmouth Amateur Television Group Includes some useful hints on setting up domestic DVB-S receivers for DATV use.

    British Amateur TV Club

    Dutch DATV Technical web site for a project that seems to have stagnated. Includes a comprehensive introduction to GMSK, QPSK and QAM.

    Finland's First DATV Station

    Kuhne Electronics/DB6NT Suppliers of superior microwave modules including DATV compatible power amplifiers

    Slovene ATV Team Web Site

    SR-Systems DVB encoder supplier. A subset of DATV products is available to amateurs via Lechner Electric.

    Yahoo UK_ATV Group Yahoo Group membership required

 

DIgital Television References In Print

    Digital Television: A Practical Guide for Engineers By Walter Fischer ISBN 3540011552

 

DATV Electronic Documents

(reproduced here with kind permission of the authors)

    ABE Digital Broadcasting Handbook (800kb PDF) As recommended by Chris Muriel G3ZDM

    AGAF DATV 2007 Update Presentation (EN) (2Mb PDF) English Language Version of AGAF DATV Update. By Uwe Krause DJ8DW

    AGAF DATV 2007 Update Notes (EN) (2Mb PDF) Notes for PowerPoint Presentation document above. By Uwe Krause DJ8DW

    AGAF DATV 2007 Presentation Original (DE) (20kb PDF) German Language AGAF DATV Update. By Uwe Krause DJ8DW

    GB3HV Digital Project Article Part 1 (160 kb PDF) By Noel Matthews G8GTZ

    GB3HV Digital Project Article Part 2 (120 kb PDF) By Noel Matthews G8GTZ

    GB3HV DATV Presentation (300 kb PDF) By Noel Matthews G8GTZ

    Video Terms and Acronyms by Tektronix (10Mb PDF) As recommended by Chris Muriel G3ZDM

 

 

 

 



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