"Postipoika" wrote in message
...
Solution for LO maybe is DDS.

That's a big "maybe" -- even the fastest DDSes aren't much better than 1GSps
or thereabouts, giving a realistic tuning range of 0-400MHz... and those parts
are quite power hungry and not at all cheap (e.g., Analog Devices' AD9858 is
several watts and nearly $50 even in quantities of 1000!). On the other hand,
one of the much lower frequency DDSes in conjunction with a mixer would
probably work well -- although it just shifts the problem to how to get nice
and pure, very wide range fixed frequencies to mix with. (E.g., DDS does
0-200MHz, so now you need just, say, a 200MHz+/-IF, 400MHz+/-IF, 600MHz+/-IF,
etc. oscillators to mix with...)

Of course with the very fine-grained frequency resolution of a DDS,
multiplying the output up would seem to be an obvious approach, but I'm told
this isn't typically used due to the relatively high spur levels of the DDS
itself.

---Joel