Thanks Henrik for this quick answer
But it is "too much" for my old brain !
Darrel has done a great job , as usual !
yes I have just one calculation (I got the Arduino code)
something like that
unsigned long tuning_word = (frequency * pow(2, 32)) / DDS_REF
frequency will go from 1 to 39 millions
DDS_REF is 125 millions
and I must decode what is the POW(2,32) !
For this need I think that I will order an Arduino board !

Happy new year for everybody
and all my congratulations for this very nice help forum, it is great
Francois F1CHF (radio amateur) 65 years old now ....