DATV- Digital Amateur TeleVision
By Michel Vonlanthen HB9AFO
These articles were mainly done when i was the the ATNA (Amateur TV of North America) representative in Europe. Badly, this association has now resumed because lack of interest and cooperation. But in french language, I have continued this serie named
Digital ATV ? This is not so complicated !
You will find in it a lot of interesting informations about DATV. If the interest is great, I can one time translate it. Intertime, you will find the DATV theory here. You will also see infos and links about ATV/DATV on my web site:
Prof.Dr.-Ing. Uwe E. Kraus, DJ8DW, received the DARC Rudolf Horkheimer
award 2002 on behalf of the DATV working group at Bergische University Wuppertal. DARC board member Dr. Walter Schlink, DL3OAP, handed over the
award to Uwe Kraus, DJ8DW, and Hans-Juergen Schmitz, DJ8VR, during the opening event of HAM RADIO 2002 fair end of June in Friedrichshafen,
Germany. In his speech DL3OAP appreciated the outstanding development by the DATV group and stressed the fact that Uwe Kraus devoted himself to
the UHF bands and the amateur television technology soon after having received his licence in 1962.
Klaus, DL4KCK, AGAF
Since November 2001 the DATV transmitter designed by a group around DJ8DW at Bergische University Wuppertal is working properly on 23 cm (1255 MHz) in Cologne at the ATV-repeater site DB0KO. The transmitter, which may be programmed to various digital modulation schemes and data rates, at this site is programmed to QPSK and according to the DVB-S standard. Thus a reception is possible by a cheap digital satellite TV set-top box along with a preamp if required. The repeater FM ATV input signal is demodulated to baseband PAL, converted to MPEG II (5 MBit/s) and digitally retransmitted.
The repeater output can be switched between FM ATV and DATV by DTMF remote control thus allowing a fair comparison. In a distance of about 50 km the FM signal (repeater output power 20 W, 18 MHz bandwidth) resulted in a rather noisy picture whereas DATV (repeater output power 10 W, 6 MHz bandwidth, same 10dB omnidirectional antenna) showed a perfect picture. Although the set-top box has no echo equalizer there were only very few problems with multipaths reception most likely due to the fact that the repeater is installed on top of a building 150 m above ground and that highly directional receiving antennas are used.
In the meantime the tests are extended in the Wuppertal area to 70 cm (center frequency: 434 MHz, bandwidth: 2 MHz, data rate: 2 MBit/s, transmitter power: some mW through 80 W). Omnidirectional as well as highly directional antennas are used. The tests are covering field strength measurements at various places in rural and urban areas, check the multipath situations as well as possible problems which might be caused by ISM interference. In addition DATV-DX tests are performed.
The MPEG II encoder board and the DATV transmitter board are currently prepared for a small-scale production series organized by AGAF. These boards ready built and tested will be available in some months time for licensed Radio Amateurs and for amateur applications only, the price is calculated on a no profit no loss base. Ordering information is available from AGAF by fax (+49 231 486 989) or via Internet at www.datv-agaf.de (commercial applications may be possible under a special contract with the Wuppertal University).
General: Both boards, MPEG II encoder and DATV transmitter, have standard signal input/output interfaces. They may be used together for DATV but also separately for other applications. The various digital modulation schemes and data rates are generated on the transmitter board with 10 mW on 434 MHz and are selectable by jumpers or switches. Modulation schemes generating 2 MHz rf-bandwidth may be transmitted on 70 cm, all others with a higher rf-bandwidth are heterodyned to the GHz bands.
1: MPEG II Encoder (Fujitsu encoder IC)
2. DATV Transmitter
The digital Amateur Television test provided by a group around
DJ8DW from Wuppertal university at the HAM RADIO 2001 fair in Friedrichshafen, Germany, was built up over a 9 km distance
from the "Elektronikschule Tettnang" building to hall 6. On 434 MHz plus/minus 1 MHz 80 watt power output were used in
GMSK modulation and a fourfold 11-el. yagi group at each location.