27-11-2019, 07:56 AM
Jac, thanks for the practical demonstration.
From memory I recall that the BBC CO6/509 digital converter used a subcarrier notch ahead of the ADC. This was to prevent the colour dot patterns being converted to something potentially horrible looking on 405. Inevitably this limits the resolution, just as it does on older colour TVs. Good comb filter decoding in PAL was always much harder than in NTSC. The TVP5150 as used in Aurora SCRF and Hedghog does a pretty good job, with minimal artefacts. I've also used the SAA7118 which isn't quite as good.
If you know your 625 source is monochrome then you don't need any filtering but the decoder can't work this out for itself unless the burst isn't present.
From memory I recall that the BBC CO6/509 digital converter used a subcarrier notch ahead of the ADC. This was to prevent the colour dot patterns being converted to something potentially horrible looking on 405. Inevitably this limits the resolution, just as it does on older colour TVs. Good comb filter decoding in PAL was always much harder than in NTSC. The TVP5150 as used in Aurora SCRF and Hedghog does a pretty good job, with minimal artefacts. I've also used the SAA7118 which isn't quite as good.
If you know your 625 source is monochrome then you don't need any filtering but the decoder can't work this out for itself unless the burst isn't present.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
