On Mon, 22 Sep 2003 16:09:09 +0100, "Ian White, G3SEK"
wrote:

I'm sorry to keep picking away at this one, but it seems to be
necessary...

The statement that a directional coupler can "separate energy by its
direction of travel" involves some unaware assumptions involving
transmission-line theory.

If we're trying to get that theory right, we have to avoid using it
unawarely in order to prove itself... because that way would let us
"prove" just about anything.

A directional coupler only senses the current (directionally) at a
particular location on the line, and the voltage between the two
conductors at that same location. The directional coupler tells us
NOTHING else. We have to be very literal-minded about that.

We cannot determine the reflection coefficient, the SWR, or what is
happening to the energy, without applying some flavor of
transmission-line theory. When the whole discussion is about getting
that theory right, we have to be very careful to avoid unawarely arguing
in circles.

Hi Ian,

It seems every time you come into conflict, you reject other's
statement as issues of circularity and confusion.

A Directional Coupler is principally a transmission line in itself, a
paired one in fact with controlled leakage between the two. There is
nothing inherently restrained in its operation that enforces this
curious complaint of
A directional coupler only senses the current (directionally) at a
particular location on the line, and the voltage between the two
conductors at that same location. The directional coupler tells us
NOTHING else. We have to be very literal-minded about that.
which as a statement means little beyond the obvious coupling that is
necessary. And to state that NOTHING else is told begs the question:
So What? Nothing else was implied, inferred or demanded, and you
offer nothing to illustrate just what it was you objected to. You
call them "unaware presumptions." WHAT presumptions are they?
Certainly not the same observation I quoted just half a dozen lines
above.

The Bird element is indeed a primitive implementation of a Directional
Coupler. It even discards phase information (in fact, it is
unavailable, but it would still be discarded through rectification and
filtering). The Bird element constitutes a three port Directional
Coupler where a four port coupler would return that phase information
(if it were not then immediately discarded through the same
rectification and filtering). The difference between what is
available and what is not is a design choice enforced by the
application of the instrument, not a shortfall of Directional Couplers
as a class of device.

Directional Couplers are literal transmission line components and the
heart and soul of network analyzers.

73's
Richard Clark, KB7QHC