DATV-Express Project – July update report

[KenW6HHC]

Charles G4GUO has been very busy during July making software improvements and adding capability for the linux implementation

• • installing the DATV-Express software on a PC running Ubuntu linux can be a little tedious-and-unforgiving if you are not experienced using linux. Charles completed building a Debian package-installer to make installing the DATV-Express software almost a one click effort. (Except the user still has to change his OS account privileges to allow access to the USB device....however this step will be well documented in the future installation guide.)
  • code has been written to access the AD7992 ADC and the 2C64 flash memory chip on the Express board.
  • revised the FFT from 16 bit fixed maths to floating point maths.
  • the USB2 loading has been reduced by using 8 bits I and 8 bits Q...rather than 32 bits, 16 bits I and 16 bits Q.
  • all the different filters are now stored in the FPGA now. So there is only one .rbf file rather than the 4 files that the project was using before.
  • improved the buffering to eliminate video drop-out on slow PC's.
  • Charles discovered that the first switching power supply (dropping 12V down to 5.5V) was creating two “switching frequency spurs” that are somehow coupled to the modulator (or buffer RF amp) and can be seen at the carrier, +/- 1.34 MHz. The board has an excellent phase noise at -120 dBc at this frequency and spurious signals are at -60 dBc. Charles can see the magnitude of the spurs rise as the RF power is increased...that is: as the power supply provides more current.

Art WA8RMC completed assembling prototype board #5 (reusing some components from the now cannibalized prototype #1 board which was earlier etch layout). Art then bogged down in time-conflicts (like painting the house) and in some linux details on trying to install the DATV-Express software in Ubuntu. He has just received the Debian software-package-installer to finally begin complete the SW installation and to actually transmit DATV video. His first plan is to see if the switching power supply RF spurs (near the carrier frequency) can be reduced by a little more filtering on the switching power supply, etc.

Ken W6HHC finished installation and testing on the DATV-Express software. One change that came about during the testing was to increase the buffering. On Ken’s slow 1.8 GHz Pentium, there was noticeable video drop-out with the original synchronous buffering. Ken reports that the video drop-out problem disappeared after the buffering re-design. Ken and Robbie KB6CJZ completed a series of bench tests of a DVB-S transmitting station using the DATV-Express board and software and published report in a newsletter article called TechTalk111 (see http://www.W6ZE.org/DATV/ ). Ken is now preparing a presentation and demo for his local radio club, OCARC, in August.

The DATV-Express exciter hardware proto #4 board is fitted with an aluminum plate as a heat-spreader


The primary goal of the team right now is to see how quickly we can update the etch and obtain about ten preproduction boards to put into the hands of some intrepid alpha testers.

“full speed ahead”...de Ken W6HHC