Owen Duffy wrote:
Has someone got a good definition of coherent.

From the IEEE Dictionary: "coherent (1)(fiber optics) Characterized by
a fixed phase relationship between points on an electromagnetic wave ...
(2)(laser maser) A light beam is said to be coherent when the electric
vector at any point in it is related to that at any other point by a
definite, continuous sinusoidal function."

An antenna may well
receive rays from a single source that are not in phase.

I receive rays from WTAW that are sometimes in phase and sometimes not
over a period of mere seconds. Earth's atmosphere seems to be a
coherence killer.
--
73, Cecil http://www.qsl.net/w5dxp