On Sun, 6 Jun 2010 14:21:16 -0700 (PDT), Keith Dysart
wrote:

The 100W forward and 50W reflected have no relation to actual powers

From a current NARDA specification:

GENERAL COUPLER OPERATION
A coaxial directional coupler has the general appearance
of a section of coaxial line, with the addition of a second
parallel section of line and with one end terminated (see
Figure 9). These two sections are known as the main and
auxiliary lines. The two lines are internally separated from
each other; the amount of spacing between lines determines
the amount of RF energy that may be transferred
from the main line to the auxiliary line. In operation, assume
that energy is fed into port A of the main line. Most of
this energy will appear at output port B of the main line.
However, a fraction of this energy (determined by coupling
value) will also appear at the coupled port C, of the
auxiliary line.
A dual-directional coaxial coupler, such as the
reflectometer coupler, consists essentially of two single-
ended couplers connected back-to-back. Perhaps
the most important characteristic of the directional coupler
(and the one from which its name originates) is its
directivity.
....
For reflectometry applications,
the dual directional coupler, incorporating two
auxiliary outputs, permits the simultaneous sampling of incident
and reflected power.
....
RF power applied to
the load is reflected to some degree depending on load
characteristics, thereby resulting in a voltage standing
wave ratio (VSWR) which is reflected back to the main line
output port. this reflected power is coupled out of the reflected
output port at a level 10 dB down from the reflected
power level at the load.

73's
Richard Clark, KB7QHC