In article ,
Joel Koltner wrote:
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...)

From reading the occasional data sheet and appnote, I have the impression
that (as Tim Wescott says) they upconvert to a high IF, like 3 GHz,
and then convert down from there.

In that case they might have an LO that tunes from 1.7-3 GHz, which is
a much smaller range, proportionally, than 100kHz-1.3GHz.

--
Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1