DATV-Express Project – November update report

[KenW6HHC]

Charles G4GUO released v1.08 software to the project team. The main change was to fine-tune and replace the “proof-of concept” v1.07 that had fixed the PCR clock-jitter problem that is caused by Hauppauge video-capture units (especially in linux). Also the organization of the GUI windows has been reorganized and is now more straightforward. Charles is working towards a final software clean-up effort before releasing the 32-bit and 64-bit software for production at the end of December. The production release of software will hopefully resolve a nagging I2C communications problem on initial startup. This I2C problem is being caused by the FPGA code design and will occasionally results in the need to power-cycle the board and restart the software.

Ken W6HHC continues to work on updating the USER MANUAL. The latest PDF draft (now 30 pages long) has now been uploaded to the project website. When Ken tested the new v1.08 software he discovered that his ancient (but trustworthy) P4 CPU running at 1.8 GHz was no longer fast enough to run the software with the new design that re-calculates the PCR clock. He partitioned his newer Win7 notebook (3 GHz dual-core CPU), loaded the ubuntu V12 LTS OS and now the v1.08 transmitter works perfectly.

Art WA8RMC reports that all production boards that he has ready for production sales, test with at least 17.5 dBm (around 55 mW) of RF output. CORRECTION - PWR MEASUREMENT was CW CARRIER!! See the following companion post for details This means the board can NOT directly drive 30W RF amplifiers with DVB-S modulation(30W FM rating like DownEast 2330PA for 1.2 GHz).

Typical System Block Diagram running DVB-S on 1.2 GHz - - SEE NEXT POSTING for a correction


Art has recruited Bob N8NT (from the ATCO club) to help set-up the http://www.DATV-Express.com website . The web site will be “under construction” for a few more weeks, so we ask you to be patient. The PayPal payment method has been tested and you can download a PDF draft of the USER MANUAL from the web site (click on DATV-Express Progress link on left-hand frame at HOME) today. Anyone wanting to help improve the basic product software is welcomed. Art explains that as an encouragement, we are asking for a US$200 purchase donation (including shipping) which is our cost. Contact G4GUO directly if you are an interested programmer and he will provide you a “PromoCode” to enter…we still have two more pre-production boards reserved for early programmers that can ship today. After that we would like to market the complete board to ATVers at about US$300 plus shipping. Our goal is to not make a profit on this project but only recoup our production/parts costs in order to provide a low cost entry into DATV for Hams. The goal for the team is to "begin taking production orders in January and then shipping immediately" .

Questions are welcome.

“Full speed ahead”...de Ken W6HHC

[KenW6HHC]

SOMETIMES the Project Team runs too fast!

Art WA8RMC went to retest the production boards at a friend with a very fancy Agilent EXA Signal Analyzer (also very very expensive). The previously reported 17.5 dBm (about 55 mW) power was measuring the CW carrier coming out of the DATV-Express board. It was expected that the DVB-S/QPSK power-out strength would be around 20-25 mW, enough to drive directly into the 30W RF amplifier. But the accurate Agilent EXA Signal Analyzer showed that in QPSK modulation CHANNEL POWER was down around 0 dBm or so (1 or 2 mW). Part of the reason for the smaller power out is some spectral-regrowth (aka "haystack" shoulders....or distortion) occurs when the DATV-Express power is cranked up above a power-setting of 35 (out of a max of 47).If you try to amplify a distorted signal...only more distortion occurs.

So if you are planning to have 6 to 8 watts of RF output...you need to plan on two stages of external RF amplifiers as shown in the block diagram below

Typical System Block Diagram running DVB-S on 1.2 GHz using two stages of external RF amplifiers


The team is sorry about creating some un-achievable expectations in the earlier November Project Report!!

"moderate speed ahead!!"...de Ken W6HHC

[G4GUO]

John G4BAO will be producing a kit I believe based on a PD85004 device which looks ideal
as a low power driver amp with 15 db gain and 2.5W output on 1.3 GHz.

- Charles G4GUO

[g8gtz]

Yes, there's a full article on the G4BAO amp in CQ-TV 242 with details on kit availability etc.

73

Noel - G8GTZ