On Tue, 27 Sep 2005 02:25:11 +0000 (UTC),
wrote:


SWR is nothing more than a dimensionless impedance ratio.

Is that so... Owen
--

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:25:11 +0000 (UTC),
wrote:


SWR is nothing more than a dimensionless impedance ratio.

Is that so... Owen
--

Yes, it is so and it is equal to:

SWR = (A + B)/(A - B)

Whe

A = sqrt ( (R + Z)^2 + X^2 )
B = sqrt ( (R - Z)^2 + X^2 )

R = resistive component of load impedance in Ohms.
X = reactive component of load impedance in Ohms.
Z = reference impedance (purely resistive) in Ohms

If you don't believe it, get some resistors, capacitors and a half
way decent SWR meter and do some experiments; no transmission line
required.

--
Jim Pennino

Remove .spam.sux to reply.

On Tue, 27 Sep 2005 02:54:31 +0000 (UTC),
wrote:

Owen Duffy wrote:
On Tue, 27 Sep 2005 02:25:11 +0000 (UTC),
wrote:


SWR is nothing more than a dimensionless impedance ratio.

The fundamental definition of SWR flows from the behaviour and
properties of RF transmission lines.

When a transmission line is terminated in an impedance other than its
characteristic impedance, there will be both a forward wave and a
reflected wave of such magnitude to resolve the conditions that must
apply at the termination.

The forward wave and the reflected wave sum at all points along the
line having regard for their magnitudes and relative phase to produce
a "standing wave". The Standing Wave Ratio (SWR or VSWR) is defined to
mean the ratio of the maximum to the minimum of the magnitude of the
standing wave voltage pattern along the line.

The SWR on a lossless line can be calculated knowing the complex
characteristic impedance of the line and the complex load impedance.

The SWR on the line does not depend in any way on some unrelated
independent reference resistance as you suggest in your formula.

You seem to be suggesting that your redefined SWR is a really good
(obscure) way to talk about an impedance (independently of a
transmission line) in terms of some standardised reference value, and
you can throw away the fundamental meaning of SWR to support your
SWR(50) concept. In your terms (independently of a transmission line),
for instance, a Z of 60+j10 would be SWR(50)=1.299, and so would an
infinite number of other Zs have SWR(50)=1.299... how is that of
value. To know Z is 60+j10 is to know more than to know SWR(50)=1.299.

Owen
--

Jim,

Perhaps there's some misunderstanding about location of the meter and
what it is measuring. Let's try to clear it up.

Would you please do us both a favour by answering the following simple
question?

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?

Antenna or Feedline?
----
Reg.

"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 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

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

Reg Edwards wrote:
Jim,

Perhaps there's some misunderstanding about location of the meter and
what it is measuring. Let's try to clear it up.

Would you please do us both a favour by answering the following simple
question?

There is a 50 ohm line feeding a 100 ohm antenna.

There is an SWR meter located at the line-antenna junction.

What does this mean?

The meter has a reading. Does the reading apply to SWR of the
antenna, or does it apply to the SWR along the feedline?

The reading is the SWR at that point.

Antenna or Feedline?
----
Reg.

An SWR meter reads the SWR of the thing connected to its output port
with respect to the reference impedance the meter was designed for.

The SWR meter reads the SWR *AT THE POINT OF CONNECTION* of the
connected system.

Not the middle of the system, not the other end (if it has one)
of the system, but the input point.

If you measure a SWR (50 Ohms reference) of 2:1 for a black box,
what is in the box?

A. A 25 Ohm resistor.
B. A 100 Ohm resistor.
C. A cable spool of coax with some impedance at the end of it.
D. Could be any of the above.

In general there is no guarantee that the SWR at any point of a
transmission line will be equal to the SWR at any other point on a
transmission line other than for special cases.

What seems to have you terribly confused is that all the transmission
lines, tuners, antennas, connectors and whatevers become a *SYSTEM*
and the SWR at the input connector to the *SYSTEM* is not guaranteed
to be the same as the SWR at some arbitrary point inside the system.

When you measure the SWR of a line with a load on the end, you are
measuring the SWR of the entire system relative to your reference,
not the load.

--
Jim Pennino

Remove .spam.sux to reply.