Two Antennas (was RE: "Blunkett u-turn on data privacy plans")

[Paul Leyland]

> Under normal 'field' conditions I agree but are you saying=20
> that this level of accuracy is impossible under any conditions?

> If someone sets out to achieve mm accuracy using GPS signals=20
> they will have
> to account for factors of the kind you mention.  This is what=20
> would be done
> in laboratory conditions and explains why it is not uncommon=20
> to find that
> laboratory measurements are orders of magnitude better than=20
> can be achieved
> in more normal situations (which explains why things often go=20
> wrong when
> people try to transfer laboratory results into the real world).

Indeed.  If the laboratory is careful enough (meaning, essentially, that =
they spend enough money) a fractional accuracy of lambda/2000 is =
exceedingly crude.

The gravitational wave people are seriously proposing to measure =
separation changes on the order of 1e-18 metres, using radiation with a =
wavelength of around 1e-6 metres.


Paul