On Tue, 27 Sep 2005 17:29:10 +0000 (UTC), "Reg Edwards"
wrote:

If's and But's are not required.
The antenna is just an arbitrary load.
Does the meter reading indicate SWR on the feedline (which is what is
usually required), or does it not?
This is not a "catch question". It is not a troll.
No, of course it isn't (must be all those other posts then)
"Antenna or Feedline?" please.
KISS

Hi Reggie,

Ah yes! That "additional information" finally surfaces as a
requirement doesn't it?

SWR "on the feedline" is like dust thrown into the eyes of the rubes
before the elephant appears in front of them. Presumably, "on the
feedline" is akin to the ark holding a sacred artifact like the finger
of St. Heavybottom.

The traditional slotted line used for probe determination of SWR comes
with two connectors like that commonplace SWR meter (and the slotted
line probe connects to a - SWR METER! albeit, not the commonplace
variety, but odd how the tide of time has not yet altered the name to
TLI). And if we were to substitute the slotted line for commonplace
SWR (or t'other way 'round), both/either/each would face the same
issues and offer the same results. Imagine that, not a whit of
difference, except that the probes can add error through in-expert
use. Whoops! Same issues of how things can/do go wrong.

So, the ultimate question of the universe (yadda-yadda-yadda) is what
difference does having a transmission line between these two
connectors make on the outcome of what SWR exists AT the load
connector? A rhetorical difference! After-all, you would need
"extraordinarily more information" to express where the SWR resided,
wouldn't you? ;-)

Any artificial constraint you toss in as an objection exists for
yourself as well. I can see Kelvinator swinging his cane now. Did I
say lower 6th? They would probably hoot you down to upper 5th.

73's
Richard Clark, KB7QHC

There is no mystery about the 'required additional information'.

The nearest the so-called SWR meter ever gets to measuring anything is
the "magnitude of the reflection coefficient", MRC, which arises due
to the impedance of whatever is presented to the meter's output
terminals. (Recall, this impedance is the 4th variable arm of the
meter's RF resistance bridge.)

This impedance can have an angle anywhere between 90 and -90 degrees.
And the MRC can have an angle in any of the 4 quadrants, ie., anywhere
between 0 and 360 degrees.

But the meter is capable of indicating ONLY the MRC. All the angle
information is lost and gone forever. This is equivalent to losing
information about the location along the line of the peaks and troughs
in the standing wave. That is, of course, if a long line extending
back from the input of the meter to the transmitter actually exists.

Now, if the line with standing wave exists, the magnitude of the SWR
can be calculated from -

SWR = (1 + MRC) / (1 - MRC)

or the meter scale can be calibrated in terms of SWR.

It is frequently thought the SWR can be used to calculate the power
lost in the line. But, particularly when the the line is less than
1/4-wavelength long, this is not so. It requires the location of peaks
and troughs to be known - which they are not.

It is also thought that by rearranging the equation it is possible to
calculate the reflection coefficient from the indicated SWR. Wrong
again - can't be done, and in any case the reflection coefficient is
useless without an angle.

So the indicated SWR is not of much use except to provide a topic of
conversation. On the other hand, just by recalibrating the meter
scale, you can have a valuable, indispensible TLI.

By the way, I hear Californian wine makers have been hijacking the
names of French grape-growing districts and have been obliged to
re-calibrate their bottles. Ah well, back to the Chilian stuff.
----
Reg.

On Wed, 28 Sep 2005 04:07:21 +0000 (UTC), "Reg Edwards"
wrote:

There is no mystery about the 'required additional information'.

Hi Reg,

Of course, no one thought so except you - until now, and you still
have nothing to offer that distinguishes the probe method from the
common SWR meter available to every CB operator.

By the way, I hear Californian wine makers have been hijacking the
names of French grape-growing districts

Boy, are you late in taking in your newspaper. This has been going on
since the American vineyards saved the French lines from a devastating
rust blight decades ago. There is no original French line that has
not been re-planted from American root cuttings for half a century or
more after the Germans tilled their soil with Stukas.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Boy, are you late in taking in your newspaper. This has been going on
since the American vineyards saved the French lines from a devastating
rust blight decades ago. There is no original French line that has
not been re-planted from American root cuttings for half a century or
more after the Germans tilled their soil with Stukas.

A lot of those American wine-making families had French roots. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
It is frequently thought the SWR can be used to calculate the power
lost in the line. But, particularly when the the line is less than
1/4-wavelength long, this is not so. It requires the location of peaks
and troughs to be known - which they are not.

In my no-tuner system of tuning, the peaks and troughs are known.
The purely resistive current maximum point is always located at
the balun/choke.
--
73, Cecil http://www.qsl.net/w5dxp