Prototype set is here

[Penthode]

Originally Posted by tubesrule

I guess I only consider CBS and today's analog color standard as NTSC since those were the ones ratified. CPA, dot sequential and the rest were only lab exercises or presentations to the NTSC.

I am envisioning an issue with CPA and compatibility with the SCRF converters. Since these converters don't have frame memories they can't do frame rate conversion. This means the line and frame timing will match modern standards so there will not be a exact relationship between the line timing and sub-carrier frequency. We would need to either shift the sub-carrier frequency slightly, or accept a non-integer relationship. Not sure if the later would be a problem as I have not seen how the set determines which field phase it's in. The more expensive WC converter can do whatever we need but is overkill.

Darryl

Darryl,

The DOT sequential system is RCA. But the CPA test came under the auspices of the NTSC. I believe Bernard Loughlin refers to CPA in the context of NTSC.

Can you explain your concern over compatibility with the SCRF?

It would seem to me that the current NTSC frame rates are acceptible for CPA since the NTSC frame rates ensure proper chroma interleaving with the presence of the 4.5MHz sound carrier.

Hence if the current scan rates are used, the standard NTSC subcarrier relationship (odd integer multiple of half the horizontal rate would suffice for the nominal 3.89MHz. But CPA means that with only a half line offset, the Y and R-Y spectra will align to form a vertical dot line up and resulting dot pattern. Hence I believe a quarter line offset is required.

The nominal 3.89MHz results in:

3890000/fH/2 = 494.4622...

The closest quarter line offset multiple is therefore 493.75

Therefore the CPA fsc = 493.75 x fH/2 = 3.884396MHz

I believe this CPA subcarrier can be used with current NTSC scan rates and provide the best interleaving of the chroma.

What do you think?

Terry