Charles had the new board transmitting DVB-S and DVB-S2 video within a couple of hours after Parcelforce delivered the box to his QTH. Charles’s first reports included:
• Min operating frequency 72.5 MHz
• Max operating frequency 2.48 GHz
• Noise sidebands -55db (about 30db better than previous board)
• Very clean QPSK constellation
First DVB-S pictures received from new board layout
On the left is the clean QPSK Constellation from new second board layout.
On the right is the noisy QPSK Constellation from original board etch layout.
During March, Charles was able to accomplish quite a lot of improvements to the DATV-Express software design, as he has summarized below:
Host code
• Now being compiled under Ubuntu 12.04 LTS
• Development environment has been updated to Qt5.01 Creator
FX2 code
Added proper support for USB2 VBUS monitoring
FPGA code
• Interpolation increased from x4 to x8
• Pulse shaping filter increased to 95 taps (root raised cosine compensated response).
• Programmable symbol rate generator added with the current range 2 MS/sec to 6 MS/sec in fractional steps.
• I2C configuration of modulation parameters has been added
• Delayed IQWRT clock added.
• DAC has so far been tested up to 48 Msamples/sec
No etch errors have been found in the second layout, so huge compliments are deserved by our PCB layout guru, Tom WB6P. Art WA8RMC is busy building up a second prototype board. Charles also has plans to get the entire DVB-S protocol to run on the FPGA rather than on the Linux host PC. That way…the whole host thing can also be run on a small ARM-based computer, like a Raspberry Pi or perhaps the MK808.
Spectrum of new board with 1.299 GHz unmodulated carrier signal
In his spare time, Charles G4GUO has completed a new YouTube video to describe
the DATV-Express Version 2 PCBA at http://youtu.be/OXh-anABYaU
"full speed ahead"...de Ken W6HHC