Andy,

But isn't the accuracy and stability of a cheap colour subcarrier xtal,
pulled more than 100ppm from its normal operating point,  going to swamp the
values you derive from the 'nice' numbers generated with integer maths ?

My idea was to use a second DDS chip as divider (with fixed "nice number"
phase increment) to get a "nice number" PLL reference frequency. The VCXO
is then the only odd-ball frequency in the system.

See attached block diagram.

73
Johan SM6LKM