"Reg Edwards" wrote:
There is a 50 ohm line feeding a 100 ohm antenna.
There is an SWR meter located at the line-antenna junction.
The meter has a reading. Does the reading apply to SWR of the
antenna, or does it apply to the SWR along the feedline?
______________

It applies to the match of the RF network that follows the SWR meter to the
impedance for which the SWR meter was calibrated.

And if in your example the SWR meter has been calibrated for 50 ohms, and is
moved to the input end of that line+antenna RF network, it will also have a
reading -- which will be the same as when it was inserted at the
antenna-line junction, less the round-trip RF attenuation of the
transmission line (assuming that the transmission line is 50 +/- j0 ohms
throughout its length).

In fact it is a common practice to optimise the transmission line/antenna
match of commercial FM and TV broadcast antenna systems by use of a variable
transformer inserted at the antenna input, whose adjustment is made by
reference to the far-end reflection seen at the sending end of the
transmission line, using a high-directivity reflectometer, or SWR meter.

The same physics applies to ham antenna systems and methods/means of
measurement.

RF

Visit http://rfry.org for FM transmission system papers.

Richard,

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.

"Antenna or Feedline?" please.

KISS
----
Reg.

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

"Richard Fry" wrote in message
...
"Reg Edwards" wrote:
There is a 50 ohm line feeding a 100 ohm antenna.
There is an SWR meter located at the line-antenna junction.
The meter has a reading. Does the reading apply to SWR of the
antenna, or does it apply to the SWR along the feedline?
______________

It applies to the match of the RF network that follows the SWR meter
to the
impedance for which the SWR meter was calibrated.

And if in your example the SWR meter has been calibrated for 50
ohms, and is
moved to the input end of that line+antenna RF network, it will also
have a
reading -- which will be the same as when it was inserted at the
antenna-line junction, less the round-trip RF attenuation of the
transmission line (assuming that the transmission line is 50 +/- j0
ohms
throughout its length).

In fact it is a common practice to optimise the transmission
line/antenna
match of commercial FM and TV broadcast antenna systems by use of a
variable
transformer inserted at the antenna input, whose adjustment is made
by
reference to the far-end reflection seen at the sending end of the
transmission line, using a high-directivity reflectometer, or SWR
meter.

The same physics applies to ham antenna systems and methods/means of
measurement.

RF

Visit http://rfry.org for FM transmission system papers.

"Reg Edwards"

"Antenna or Feedline?" please.
KISS
___________

Antenna.

And a big smooch to you, too.

RF

"Reg Edwards"

"Antenna or Feedline?" please.
KISS
___________

Antenna.

And a big smooch to you, too.

--------------------------------------

Rich, thanks for the smooch.

But I'm afraid you are wrong. The meter correctly indicates SWR on
the feedline when it is located at the antenna end of the line.

But don't worry too much about it. It seems you are in good company.
So much for the technical education of radio engineers.

It all comes about because of so-called SWR meters being called SWR
meters - which they are not. At least not when located at the
transmitter end of transmission lines as they nearly always are.

When located adjacent to the transmitter they are TLI's. Transmitter
Loading Indicators. And SWR has very little or nothing to do with it.
----
Reg.

"Reg Edwards"
But I'm afraid you are wrong. The meter correctly indicates
SWR on the feedline when it is located at the antenna end
of the line.
______________

Remove the feedline, and connect the 100 ohm antenna through the SWR meter
calibrated for 50 ohms, directly to the transmitter. The meter has a
reading. The measurement will have the same value as before, neglecting any
adjustment for having no line loss now. But there is no feedline, so how
can there be any SWR on it, you write.

The fact that there is not enough transmission line length in the system for
literal standing wave maxima and minima to develop on it does not mean that
reflections do not exist in the output load system. It is the value of
those reflections that determines the corresponding value of SWR.
Reflections can be measured by appropriate instruments regardless of the
length of line in the measured system, or even the existence of any
transmission line at all.

The convention of the professional engineering community for many decades
has been to convert incident and reflected waveform samples into the
corresponding value of SWR, no matter if there is insufficient line length
in the system for the corresponding maxima and minima to develop fully on
it. It doesn't matter, electrically. Your constant diatribes stating that
it does is a futile exercise.

Disable the SWR protection in your ham tx and key it to full power into an
open or short. There is no transmission line where standing wave maxima and
minima could exist, but your tx will burn up anyway.

Maybe save your response until tomorrow morning, when your Merlot buzz has
worn off

RF

"Reg Edwards"
But I'm afraid you are wrong. The meter correctly indicates
SWR on the feedline when it is located at the antenna end
of the line.
______________

PS:

In this example the mismatch between the antenna and the line is the source
of the reflection that results in system SWR. Convention is to state that
the SWR belongs to the antenna, not the line -- although the added stress on
components applies only to the line and tx, and not to the antenna.

An ideal SWR meter will read that antenna reflection to have the same value
when installed at either end of the line, or anywhere along its length
(assuming
a perfect 50 ohm line, and neglecting line loss).

RF

Reg Edwards wrote:
"Antenna or Feedline?" please.

If the meter is calibrated for the feedline Z0, it will read
the SWR on the feedline.

If the meter is calibrated for the antenna Z0, it will read
the SWR on the antenna.
--
73, Cecil http://www.qsl.net/w5dxp

Cec, you can make the meter read anything you like just by twiddling
the calibration pot. Of what bloody use is that? !**?!!

Just answer the obvious question. No If's or But's
----
Reg.


"Cecil Moore" wrote in message
...
Reg Edwards wrote:
"Antenna or Feedline?" please.

Reg Edwards wrote:
Cec, you can make the meter read anything you like just by twiddling
the calibration pot. Of what bloody use is that? !**?!!

Just answer the obvious question. No If's or But's

I did answer the question, Reg. You just didn't like the
answer.

Let's say we have an SWR meter at point 'x' in the following
diagram:

XMTR---1WL 50 ohm coax---x---1WL 75 ohm coax---100 ohm load

If the meter is calibrated for 50 ohms, it will indicate the
SWR on the 50 ohm coax, 2:1, on the source side of the meter.

If the meter is calibrated for 75 ohms, it will indicate the
SWR on the 75 ohm coax, 1.33:1, on the load side of the meter.

An SWR meter samples the magnitude and phase of the voltage,
samples the magnitude and phase of the current, assumes
it exists in the Z0 environment for which it was calibrated,
and accurately reports those results.

If the SWR meter is installed in a Z0 environment other than
that for which it was calibrated, the instrument is being
misused and the operator is at fault, not the instrument.
Any instrument can be misused.
--
73, Cecil http://www.qsl.net/w5dxp

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