I am sorely tempted but will refrain from calling the whole lot of you a
bunch of old wives.

Kindly desist in trying to put words into my mouth.

I have NOT said that changing the source impedance changes the SWR
indication. It doesn't !

I HAVE said that if the line is NOT 50 ohms then the SWR reading, even if it
doesn't change, BECOMES GROSSLY INCORRECT !

So "in practice", even if there IS a line of some sort, as you don't know
what the line impedance or generator impedance is, then the SWR indication
and the reflection coefficient from which it is derived are MEANINGLESS,
USELESS !

As Tarmo must by now be exhausted in repeating, and I have been saying for
years, all the meter tells you is whether or not the complex load on the
transmitter deviates in some unknown diirection from a purely resistive 50
ohms.

That is what the thing is there for. Which is all anybody needs to know
anyway.

Even to mention SWR in the present context dis-orients novices and
earners - which we all were at some time or other.

So change the name of the instrument to TLI. It's not a meter anyway.

I also have reservations about so-called reflected power. But that's another
matter.
----
Regards, Reg, G4FGQ

If the reflected and forward powers are known and the Bird is a short or
zero distance from the transmitter, why would anybody want to know the
reflection coefficient and SWR anyway?

Of what use are they except to use the graphical calculator to calculate the
forward and reflected powers?

It seems the Bird designer was wise enough to omit the SWR scale from the
meter.
---
Reg G4FGQ

Reg`s statement:
"But it DOES affect the indicated SWR and so the indicated SWR is
incorrect." does not apply to the Bird Model 43 wattmeter.

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

I've never seen one but there's nothing special about a Bird. It behaves
exactly the same as those from other manufacturers.

If the line between generator and meter is NOT 50 ohms then the actual SWR
on that line is NOT the value indicated by the meter. As I said, the
indicated SWR is incorrect.

It is important to distinguish between indicated and actual SWR's. It is
fatal to worship the meter as being error free and so make the same
incorrect assumptions as the meter does.
----
Reg, G4FGQ

Reg Edwards wrote:
I am sorely tempted but will refrain from calling the whole lot of you a
bunch of old wives.

Kindly desist in trying to put words into my mouth.

I have NOT said that changing the source impedance changes the SWR
indication. It doesn't !
. . .

I posted:

Source impedance DOES affect the amount of energy moving in and sloshing
around in a transmission line. It DOESN'T affect the ratio of forward to
reflected waves, and therefore DOESN'T affect the SWR.


To which you replied:

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

But it DOES affect the indicated SWR and so the indicated SWR is incorrect.

and:

If the source is not what the meter expects then it gives the wrong answers.
And its faithful worshippers believe it!

=========================== End of quote

Better check on the worm-wood content of that wine you've been drinking.
Another tip is to save a copy of each message you post. Then when you
encounter that blank spot in your memory, you can at least read what you
posted the night before.

Sad, isn't it, when the Old Wives can remember stuff you wrote better
than you can.

Roy Lewallen, W7EL
-- Again confirmed as a Reg's Old Wife

"Ian White, G3SEK" wrote
Everybody knows that the meter only claims to indicate rho/SWR on its
"downstream" (load, antenna) side. It doesn't claim to say or know
anything about rho/SWR on the upstream (generator, TX) side.

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

Ian, there must by a dictation error in the foregoing. Would you care to
correct it ?

However, it must be admitted, when the only transmission line at the station
is between meter and the antenna such a mistake must be fairly common
amongst the ignorant.
----
Reg, G4FGQ

Better check on the worm-wood content of that wine you've been drinking.
Another tip is to save a copy of each message you post. Then when you
encounter that blank spot in your memory, you can at least read what you
posted the night before.

Sad, isn't it, when the Old Wives can remember stuff you wrote better
than you can.

Roy Lewallen, W7EL
-- Again confirmed as a Reg's Old Wife

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

Dear Roy, a display of annoyance signifies weakness of argument.
----
Reg

Reg Edwards wrote:
"Ian White, G3SEK" wrote
Everybody knows that the meter only claims to indicate rho/SWR on its
"downstream" (load, antenna) side. It doesn't claim to say or know
anything about rho/SWR on the upstream (generator, TX) side.

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

Ian, there must by a dictation error in the foregoing. Would you care to
correct it ?

No - I meant exactly what I said. The meter can only indicate the
rho/SWR of whatever is connected downstream (load side) of the meter
itself.

Whatever is upstream is merely an RF source. Both the forward and
reflected readings are determined by the power level of the source
(obviously) but they are both affected in the same proportion, so the
rho/SWR result stays the same - as it must, because rho/SWR is only
affected by downstream conditions.

However, it must be admitted, when the only transmission line at the station
is between meter and the antenna such a mistake must be fairly common
amongst the ignorant.

We seem to be talking past each other, Reg, not to each other. Since
neither of us is "ignorant", each of us must be saying something that
the other one is missing.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

"Ian White, G3SEK" wrote -
No - I meant exactly what I said. The meter can only indicate the
rho/SWR of whatever is connected downstream (load side) of the meter
itself.

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

(1) I'm sure we are agreed our meters will correctly indicate Rho and SWR
only on 50-ohm lines.

(2) Insofar as the meter is concerned the transmitter's load impedance is
the input impedance of the transmission line between the meter and the
antenna. There may or may not be an intervening Z-match network.

(3) Insofar as the transmitter is concerned the line between meter and
antenna can be ANY impedance. It is desirable only that line length with its
Zo transform the antenna input impedance to somewhere near to 50 ohms (Like
a G5RV on 14.15 MHz). If things become difficult then a Z-match can be
inserted. Once we have selected Zo for this line we are no longer
interested in its SWR. And if we WERE interested a 50-ohm SWR meter would
be incapable of correctly measuring it.

(4) Note that when a Z-match is located at the transmitter end of this
feedline, and varied, the actual SWR on this line cannot change - yet the
SWR meter responds readily to the Z-match settings.

(5) The only line which, ideally, MUST be 50 ohms coax and have a small
SWR, certainly if it is of appreciable length, is that between the meter and
the transmitter. Otherwise the load directly presented to the transmitter
would not be 50 ohms. Any other impedance would transform the 50 ohms seen
immediately on the antenna side of the meter to some other value.

(6) It is the SWR on this line which the meter indicates. (If this line is
NOT 50-ohms then the meter incorrectly indicates the standing waves on it.
Which is what I said before and a lot of people disagreed. Not that a false
indication is of great consequence when it is the incorrect choice of line
Zo where the problem arises.)

(7) In practice at HF the length of this 50-ohm coax is often negligible.
The meter is often inside the transmitter box. As the misleading idea of
standingwaves on this short, even zero-length coax is nonsense the name of
the instrument should be changed to TLI. (Transmitter Loading Indicator).
Which is all that it is!

( 8) Then the topic of conversation on this newsgroup can then diverted
back to where it belongs - the far more important non-measured SWR on the
main feedline to the antenna.
----
Reg, G4FGQ

To anybody interested.

We have a HF Transmitter + 50-ohm coax + SWR meter + Tuner + Feedline of any
Zo + Antenna.


Suppose it is all tuned-up and ready to go. The transmitter is loaded with
exactly 50-ohms resistive.


Now change the 50-ohm coax to shorter length of 75-ohm Zo.


As everybody agrees (after perhaps a little meter recalibration) the SWR
meter indication will not change. BUT THE TRANSMITTER WILL NOW BE
INCORRECTLY LOADED.


Where does the inconistency lie ? Does it lie in the change in effective
source impedance?

Reg Edwards wrote:
However, it must be admitted, when the only transmission line at the station
is between meter and the antenna such a mistake must be fairly common
amongst the ignorant.

If I read what Richard said correctly, the Bird has a built-in
50 ohm transmission line. And what about the coax connection from
the source to the Bird? The guys over on sci.physics.electromag
said that two feet of 50 ohm coax guarantees a 50 ohm environment
for a wattmeter.
--
73, Cecil http://www.qsl.net/w5dxp



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