Quote:
Originally Posted by Hybrid tellies
Looks interesting. Is it possible to include accurate timing pulses ones which VCR's can sync up to.
|
That's a whole different game. The original prject is for a static image hence the teletext will also be static. Generating full teletext, with a clock running etc, is a more complex job. Undoubtedly possible but a lot more work. The work done by Fabrice Bellard and others using a PC VGA output as an arbitrary waveform generator might well be useful. He has achieved, for example, a full spec DVB modulated signal this way.
Quote:
|
I'm still not quite getting it. Attached image shows 4.43MHz "analog" signal and above it an attempt to generate the same waveform by encoding the signal at 12MHz. OK, the sampled version would be subsequently filtered to some degree but would would be the effect on the colour on a TV?
|
The reconstruction filter after the DAC puts the signal back together. When the sampling frequency is only just over the Nyquist limit (say 13.5MHz sampling a 4.43MHz SC) the sample sequence will usually look very odd.
Doing a colour coder at 13.5MHz is a bit tricky. For one thing when you do the multiplications for U and V modulators you almost inevitably get signals that go over the Nyquist limit. It's much easier at 27MHz.