Reg Edwards wrote:

"Ian White, G3SEK" wrote
And the conclusion of these experiments? That the concept of "reflected
power" is not helping us to understand anything.

============================

I've been saying for years, the so-called SWR-meter is itself the root of
the trouble - it has forward and reflected power scales on it. So it is
impossible to refer to it without becoming emotionally involved with the
highly misleading reflected power notion.

Furthermore, the confounded thing doesn't even measure SWR. How can it
measure SWR on a transmission line which does not exist?

It is a ridiculous, meaningless situation. People drag themseves off to UHF
to air their knowledge about such things as echos, S-parameters, circulators
and high power TV transmitters. Quite irrelevant to the notion of reflected
power at 1.8 MHz.

All that's necessary is to erase the meter scales, or at least wash them
from our minds, and change the name of the SWR meter to the TLI.
(Transmitter Loading Indicator). Or some other more appropriate name.

Technically correct, but far too late. "SWR" is everywhere - the genie
is out of the bottle, and it won't go back.

To expand on what Reg already knows, but clear needs to be said again
and again...


The only way forward is for everybody to understand that SWR numbers are
just one of several alternatives for judging the "goodness" of an
impedance match to some specified reference impedance. Other
alternatives include reflection coefficient, return loss, gamma, S11,
etc.

All these alternatives are equally valid, and any one can easily be
converted to any other by doing a small amount of math. RF engineers do
it all the time, and it's absolutely no big deal.

If you're only using "SWR" as a number that indicates the goodness of an
impedance match, you can legitimately apply it to *anything* that
possesses an impedance (it doesn't need to have waves standing on it).

The discussion goes off the rails when someone starts to imagine that an
"SWR meter" is truly *measuring* standing wave ratio. It isn't - it is
actually measuring one of those other quantities (magnitude of
reflection coefficient). Then there has to be a mathematical conversion
from that number into the more familiar SWR number, which is done by
calibrating the meter scale in a specific non-linear way.

It's vital to understand that difference: the instrument is *calibrated*
in SWR, but it is actually *measuring* something else.

Likewise it's a mistake to believe that a Bird Thruline wattmeter is
measuring "forward and reflected watts". It is just another gadget for
measuring reflection coefficient, with a fixed sensitivity that allows
the meter scale to be calibrated in watts. But it's only a calibration
in terms of power - the Bird is not making a power measurement.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek