26-11-2019, 03:06 PM
The Domino was compromised by a low input sampling rate. ISTR it was only 10MHz which gives a theoretical 5MHz BW on the 625 side. With excellent filters ahead of the ADC you'd get about 4MHz in practice. With simple filtering it would be less. So the 405 BW would be about 2.6MHz at best. In practice it's rolling off at 2MHz. When I had one on my bench I connected the video output to a high quality monitor and the picture was very obviously soft.
Why 10MHz? Not sure, but ISTR it used a pair of PIC processors to do the timings and that was the best they could manage.
Darius's design suffers from the limited BW of the CCD delay lines. These were intended as chroma delays in PAL decoders and hence had limited BW.
If you use modern decoder chips at the front end it's a lot simpler. They use oversampling to minimise the analogue filtering requirements. The video comes out at the professional 601 standard of 13.5MHz sampling. The only question is whether the decoder uses a notch filter or comb filter. The Aurora SCRF and Hedghog use the TVP5150 which has a good comb and hence full BW. The original Aurora (very rare) used a SAA7113 which only has a notch. Just like in most colour TVs. But it had an S video input which you could feed directly with monochrome sources (or colour if you didn't mind the dot crawl being converted to 405) and that gave full BW.
Why 10MHz? Not sure, but ISTR it used a pair of PIC processors to do the timings and that was the best they could manage.
Darius's design suffers from the limited BW of the CCD delay lines. These were intended as chroma delays in PAL decoders and hence had limited BW.
If you use modern decoder chips at the front end it's a lot simpler. They use oversampling to minimise the analogue filtering requirements. The video comes out at the professional 601 standard of 13.5MHz sampling. The only question is whether the decoder uses a notch filter or comb filter. The Aurora SCRF and Hedghog use the TVP5150 which has a good comb and hence full BW. The original Aurora (very rare) used a SAA7113 which only has a notch. Just like in most colour TVs. But it had an S video input which you could feed directly with monochrome sources (or colour if you didn't mind the dot crawl being converted to 405) and that gave full BW.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
