Fwd: DATV

[prinaldo@mindspring.com]

Gang,

FYI. Uwe is scheduled to be in the Washington area in June to talk with us about digital amateur TV. See the www.amrad.org Web site for details.

Paul, W4RI

"Prof. Dr. Uwe E. Kraus" <krausue@uni-wuppertal.de> wrote:
> Dear Paul,
due to the fact that my laboratories and my office had to move to an other building, an operation which took longer than planned, my answer to your questions is somewhat delayed.

You can find infos about earlier publications on the web under 
www. darc.de/distrikte/g/datv/datvindex.html  
Infos about research activities of the Chair of Communications Technology at Bergische University at Wuppertal/Germany you find under
www.uni-wuppertal.de/FB13/LNT/welcome.html

The 3rd generation of Digital Amateur Television (DATV) has made some progress. The new transmitter board is ready and is working. It is an Eurocard accepting MPEG 2 data at one end and delivering 10 dBm on 434 Mhz at the other end. The modulation for the time being is GMSK, the MPEG 2 transport stream is currently 2 Mbit/s but can be set until about 8 Mbit/s depending on the MPEG 2 source and the picture quality wanted. There is also 48 M non volatile memory on board containing a 24 s long moving picture sequence that can be transmitted periodically for longer test purposes.
The GMSK is generated at 36.2 Mhz IF and then heterodyned to 434 Mhz by means of a mixer and a 470,2 Mhz cristal controlled oscillator. The 36,2 Mhz signal is also available. We did also some tests already on 13 cm, mixing the 36.2 Mhz signal first to 140 Mhz and then to 2407 Mhz. Converting the 434 Mhz signal to 1255 Mhz is in preparation.
For transmission on 70cm the 10 dBm signal on 434 Mhz is amplified to 10 W using a 30 dB power module and to 100 W using a rf-concepts power amplifier.
The receiver heterodynes the 434 Mhz constant envelop signal to 36.2 Mhz. The if-limiter amplifier uses Motorola IC`s for amplification and FM demodulation. The selectivity is achieved by SAW filters having a bandwidth of 2 Mhz and a center frequency of 36.2 Mhz .
The demodulated signal is sliced and latched thus creating the baseband serial MPEG 2 transport stream along with a 2 Mhz clock signal recovered from the the sliced data.
The data are then serial to parallel converted and fed into a Fujitsu MPEG decoder board delivering RGB or PAL or NTSC,
There is no forward error correction and no channel equalization yet, but the interfaces are there to add these blocks later after having carried out more field test to learn what is really required for this application. It turned out that the receiver delivers an almost errorfree signal down to about - 82 dBm at the antenna, also ghosts are not a serious problem if high directivity antennas on both sides are used.
Currently we are designing a new MPEG encoder Euroboard applying a Fujitsu single chip encoder for both vision and sound to replace the first generation where a Philips encoder IC was used, I was not very happy with the overall performance since there were no B-pictures and there was no sound.
The modulation schemes possible with the 3rd generation transmitter board  beside GMSK are also MSK, QPSK, QAM and 8-VSB according the ATSC standard. QPSK might be interesting for 23 cm since the signal can be directly demodulated by a digital satellite set-top box getting cheaper and cheaper. There different modulation schemes are stored on the board and can be loaded by setting some jumpers.
In Friedrichshaven I will present a paper about all recent developments and tests. The demo depends on the number of volonteers to help. Next weekend we will discuss this issue and hopefully come up with committments and decisions. The minimum will be a demo of the equipment during the paper presentation with no help required. A possibility I would like to realized but still to be discussed is a transmission from a mountain in Austria across the lake to the exhibition hall.
A visit to Washington and a presentation/discussion/maybe demo is planned and I will be available on June, 23 as you proposed. In the meantime I contacted my friend Charlie Rhodes and I am welcome to stay in his house for some days, maybe he will join us since he is very interested in digital TV in general and in ATSC in particular, of course.
Paul, if there are more questions please let me know, let`s keep in touch and discuss the details of the visit in the weeks to come.

vy 73

Uwe, DJ8DW, PA3ACY