"Reg Edwards" wrote (clips):
Yet another reason why the so-called swr meter does not
measure swr is because there is no transmission line
(between meter and transmitter) on which to measure it.
SWR on it cannot not exist.

The indication displayed by that meter is the result of the match of the
transmission line and antenna connected to the output of the transmitter to
the value for which the meter was designed and calibrated. Certainly it is
possible for SWR to exist in this RF system in normal use, and the meter
measures its value.

My objection to current practice arises because the invalid
name of the instrument, plus all the arguments which arise
in futile attempts to justify it, cause nothing but emotional
confusion amongst novices and old-wives alike.

The generic function of this meter is to measure the degree of match between
a source and a load. It is not a direct measure of SWR. When properly
designed, it is a measure and comparison of voltages developed by the
incident and reflected power in the system as they pass a sample point.

There may not be enough transmission line in the RF system for the standing
wave pattern itself to develop on it fully. It doesn't matter. The ratio
of forward to reflected power in the system will be the same as if there WAS
enough line, and that is what the meter measures.

The meter could be calibrated in units of return loss, reflection
coefficient, or SWR -- all of which have corresponding equivalents. A
return loss of 26.45 dB = 4.76% reflection coefficient = 1.1:1 SWR, for
example.

The historical convention for this meter is to calibrate its display in
units of SWR. Or the meter scale could just have three zones: Good - ? -
Bad, which would do away with all these troublesome technical terms and the
objections they elicit from some (nudge, nudge). No offense.

RF






Ian, without wishing to cause the slightest offence, I'm afraid your long,
ingrained, aquaintance with the old-wives' tales surrounding swr meters is
preventing you (and others) from seeing things from a different point of
view.

The instrument is just a 4-arm RF resistance bridge, the arm subject to
variation being the input impedance of the transmission line to the
antenna
which can be any Zo you like. The other 3 arms are fixed.

The 'meter' merely indicates whether or not the input impedance of the
line-to-the-antenna is some special value of ohms (usually 50) because
that
is the desired transmitter load.

It won't, and cannot even, tell you what the value of that special value
actually is except under the very exceptional condition that it is exactly
correct.

And it tells you absolutely nothing else about what exists or is going on
in
the station unless you deduce and add to it what you already know by other
means anyway.

My objection to current practice arises because the invalid name of the
instrument, plus all the arguments which arise in futile attempts to
justify
it, cause nothing but emotional confusion amongst novices and old-wives
alike.

So why not just change the name to TLI (Transmitter Loading Indicator) and
all the confusion and arguments will cease. Novices will no longer have to
be re-educated about the true meaning and relevance of swr.

Or YOU can choose a new name if you wish and take the credit for it.

No circuit changes are needed. ;o)
---
Regards, Reg, G4FGQ

Richard Fry wrote -
The generic function of this meter is to measure the degree of match
between
a source and a load.

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

Exactly! So let's call it a TLI. Which is what it actually is. Abolish
the source of confusion and the arguments on what it does.

Of what use is the swr to anybody anyway, even when you think you know what
it is? What do you do with it? What does it tell you that you don't
already know?
---
Reg

In message , Reg Edwards
writes
Richard Fry wrote -
The generic function of this meter is to measure the degree of match
between
a source and a load.

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

Exactly! So let's call it a TLI. Which is what it actually is. Abolish
the source of confusion and the arguments on what it does.

Of what use is the swr to anybody anyway, even when you think you know what
it is? What do you do with it? What does it tell you that you don't
already know?
---
Reg



Call it an RLR meter, which is what it IS really measuring.
Ian.
--

Ian Jackson wrote:
Call it an RLR meter, which is what it IS really measuring.

How about an "SVI", Superposed Voltage-sample(+/-)Current-sample,
named for the math function that it is performing?
--
73, Cecil http://www.qsl.net/w5dxp


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"Reg Edwards" wrote:
Of what use is the swr to anybody anyway, even when
you think you know what it is? What do you do with it?

You strive to minimize it.

What does it tell you that you don't already know?

You won't know anything about the degree of match between a source and its
load without a means of measuring it. It doesn't matter whether we state
the result of the measurement in units of SWR, return loss or as a
reflection coefficient -- they all give the same information, and allow the
same action to be taken as a result.

To be accurate and valid, none of these units requires measurements to be
taken with some discrete length of transmission line between the source and
the load -- including SWR.

RF

Richard Fry wrote:
"It doesn`t matter whether we state the result of measurement in units
of SWR, return loss, or as a reflection coefficient -- they all give the
same information -- ."

Correct. The units above are fungible. All are an expression of the
mismatch of a load to the Zo of the transmission line.

With a Bird wattmeter, the reflection coefficient (rho) is the sq. rt.
of the reflected power divided by the forward power.

SWR = 1+rho / 1-rho

Return loss in dB = 20 log (rho)

Return loss in dB = 10 log (Ref.Pwr./Fwd.Pwr.)

Rho = (ZL/Zo)-1 / (ZL/Zo)+1

None of the expressions above include the source Z, therefore it does
not apply.

Best regards, Richard Harrison, KB5WZI

"Reg Edwards" wrote

let's call it a TLI. Which is what it actually is. Abolish
the source of confusion and the arguments on what it does.
_____________

Afterthought... if you call it a TLI, is that really less confusing? The
term "Transmitter Loading Indicator" could apply to a way to display the
amount of power at the tx output terminals, and show nothing of the quality
of the load that is dissipating that power (e.g., the degree of match
between the source and the load).

RF

On Fri, 3 Sep 2004 14:14:57 +0000 (UTC), "Reg Edwards"
wrote:

|Richard Fry wrote -
| The generic function of this meter is to measure the degree of match
|between
| a source and a load.
|
|--------------------------------------------------------
|
|Exactly!

Not!

The source plays no role at all. The degree of match that is
indicated is that between the line (or system Zo) and the load Z.

A 50 ohm instrument with a 50 ohm termination shows a reflection
coefficient (or whatever mathematical equivalent you want to use) of
zero regardless of the source impedance.


|So let's call it a TLI.

Let's don't. That's just more bafflegab. Suppose the source impedance
is 25 ohm and the load is 50 ohm. By this new monstrosity of a
definition, the source should be delighted when the "transmitter
loading indicator" says---well---I'm not sure what it says, but I
think the desired number is either 0 or 1. And another source
(transmitter) with a source Z of 100 ohm should be equally happy.
Right?


|Which is what it actually is. Abolish
|the source of confusion and the arguments on what it does.


I'm all for abolishing the confusion too, so why did you add to it?

"Wes Stewart" wrote (clip):

"Reg Edwards" wrote:
|Richard Fry wrote -
| The generic function of this meter is to measure
| the degree of match between a source and a load.
|--------------------------------------------------------
|Exactly!

Not!
The source plays no role at all. The degree of match that is
indicated is that between the line (or system Zo) and the load Z.
A 50 ohm instrument with a 50 ohm termination shows a reflection
coefficient (or whatever mathematical equivalent you want to use) of
zero regardless of the source impedance.
__________

I wrote "BETWEEN a source and a load," not OF the source
and a load. There is a difference.

RF

Richard Fry wrote:
"Wes Stewart" wrote (clip):

"Reg Edwards" wrote:
|Richard Fry wrote -
| The generic function of this meter is to measure
| the degree of match between a source and a load.
|--------------------------------------------------------
|Exactly!

Not!
The source plays no role at all. The degree of match that is
indicated is that between the line (or system Zo) and the load Z.
A 50 ohm instrument with a 50 ohm termination shows a reflection
coefficient (or whatever mathematical equivalent you want to use) of
zero regardless of the source impedance.
__________

I wrote "BETWEEN a source and a load," not OF the source
and a load. There is a difference.

The only difference between those two terms is that "match between" is
normal and grammatical technical usage; and "match of" ain't neither.

Wes is correct. What the meter measures is the match (expressed as
reflection coefficient, SWR, whatever) between the system Zo for which
that meter was designed and calibrated, and the load Z.

The meter measures nothing that involves the source, except the level of
RF that it supplies. It does not respond in any way whatever to the
source impedance.


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