You don't necessesarily need to have a carrier wavelength smaller than the
distance you want to measure, as long as you can accurately measure phase.
Assuming that you could measure phase to 10 degrees, for instance, a 1cm
accuracy would only require 900MHz (33cm).

Surveyor-quality differential GPS uses the 2.4GHz GPS carrier and measures
the differences in the carrier phase (not the phase of the pseudo-random
sequence) to get sub-cm accuracies.

"Paul Keinanen" wrote in message
...
On Mon, 26 Jan 2004 16:55:44 -0800, "Tim Wescott"
wrote:

-- snip --

However, in this case the accuracy requirement was 1 cm, so I guess
that at least 10 GHz (3 cm) radiation should be used.

Paul