On Mon, 23 Mar 2009 23:39:42 GMT, Owen Duffy wrote:

My observation is that convention is the use the antenna connector or w/g
flange as a reference point for such calcs. It may even be laid down in
standards... but I am not sure. Someone else may know?

Hi Owen,

What you describe is typically called the "reference plane" in
metrology. This is a term that is found in many standard methods of
RF measurement. Most often it is a point that is neutral to the
introduction of new variables (and concommittant error). To achieve
this neutrality, it must be an access point that is reproducible -
hence the association with the connector or flange as these are
controlled points of access. Connectors can be measured separately to
validate their contribution to error and variability as they can
typically be mated to instrumentation whose own connectors have been
validated by more rigorous means.

There are other issues with the reference plane, one of which is heat
transfer through it which should ring bells here.

73's
Richard Clark, KB7QHC