Richard Clark wrote:
Hi Ian,

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

Now that you mention it, that could indeed be a common factor at the
root of this newsgroup's chronically unresolved arguments.

A Directional Coupler is principally a transmission line in itself, a
paired one in fact with controlled leakage between the two.

Some UHF/microwave directional couplers consist of a primary
transmission line (the 'through' line) and a secondary transmission line
for sampling; but not all directional couplers are of this type. Many
types of directional coupler contain no kind of secondary transmission
line. Some have a bridge configuration - for example the Bruene bridge
and the resistor bridge.

At HF through VHF, even the Bird element is better analysed as an
electrically small loop that samples V and I components from the main
line, and not as a section of secondary transmission line. You only need
to consider a Bird element as a secondary transmission line at
frequencies where the loop dimensions are a significant fraction of a
wavelength, so its distributed properties become important.

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.

It was all there, but you missed it. Possibly your mind was on your own
reply.

You
call them "unaware presumptions." WHAT presumptions are they?

The presumption is that a directional coupler directly samples power,
when in fact it doesn't. It samples voltage and current separately. The
sampled current is passed through a resistor to develop a second
voltage, and then these two RF voltages are either added or subtracted.
Finally the resultant RF voltage is detected.

Nowhere in this process is there anything that could be described as
directionally sampling power. So any argument about transmission theory
that calls upon that unfounded notion as part of its "evidence" is not
going to get us anywhere useful.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

On Mon, 22 Sep 2003 22:46:24 +0100, "Ian White, G3SEK"
wrote:
You
call them "unaware presumptions." WHAT presumptions are they?

The presumption is that a directional coupler directly samples power,
when in fact it doesn't. It samples voltage and current separately.

Hi Ian,

A Directional Coupler consists of two transmission lines.
Transmission Lines are the media through which B/H waves migrate
inexorably fixed together. The premise (which you alone bring as a
clouded presumption) that the Bruene bridge somehow works with
independence from this is simply a convenience in discussing its
operation, a convention of discussion at best and not a reality.

73's
Richard Clark, KB7QHC