"Henry Kolesnik" wrote in message ...
I'm probably not the only one that is getting an adequate fill of facts,
opinions and quotes. I have only one request. Does anyone have verifiable
and repeatable evidence that a properly tuned pi network final amplifier
without a tuner does or does not dissipate power when there are reflections?
If they do can they please direct us to the source or give us an easliy
understandable write up.


If you read Chapter 13, "RF Power Amplifiers and Projects", in the
2004 ARRL Handbook, there are pages and pages of discussion of
matching plate or transistor output impedances to 50 ohms output and
not once do they ever refer to output networks dissipating or
reflecting reflected power. Not once. It's always a matter of simply
matching one impedance to another to provide the highest power output
consistent with required linearity, while staying within the
amplifiying device's ratings.

Transmission lines have reflections; output matching networks and
tuners don't. The reflections on transmission lines don't make it past
the end of the transmission line -- that's where the reflections take
place. Beyond the end of the transmission line, the reflections are
seen as mere impedances created by standing waves, which are created
by reflections, assuming mismatch.

Al

On 27 May 2004 21:16:44 -0700, (alhearn) wrote:

If you read Chapter 13, "RF Power Amplifiers and Projects", in the
2004 ARRL Handbook, there are pages and pages of discussion of
matching plate or transistor output impedances to 50 ohms output

Hi Al,

Watch it, this is a heresy. ARRL is certainly not the end-all be-all
of design advice, but given these points are confirmed by professional
design guidelines and technical papers, one should be able to trust it
as a source written at a level suitable for amateur introduction.

and not once do they ever refer to output networks dissipating or
reflecting reflected power. Not once.

However, absence of discussion does not necessarily mean there is an
absence of concern.

It's always a matter of simply
matching one impedance to another to provide the highest power output
consistent with required linearity, while staying within the
amplifiying device's ratings.

Simple logic dictates as much.

Transmission lines have reflections; output matching networks and
tuners don't.

Simple logic does not allow this however. However, verifying this
property would be rather a challenge.

The reflections on transmission lines don't make it past
the end of the transmission line -- that's where the reflections take
place.

True, but only insofar as the tuner is adjusted to offer a conjugate.

Beyond the end of the transmission line, the reflections are
seen as mere impedances created by standing waves, which are created
by reflections, assuming mismatch.

Again, true after a fashion, but the distinction is only a matter of
point of view. Wave mechanics/lumped circuits give the same result.

73's
Richard Clark, KB7QHC

Richard said -
True, but only insofar as the tuner is adjusted to offer a conjugate.

================================
Richard, how many more times do I have to tell you? The impedance looking
back into the tuner is NOT the conjugate of the impedance looking into the
transmission line towards the antenna - not even when the tuner is adjusted
for SWR = 1-to-1.

You lead people astray.

Or did you make the assertion just to irritate yours truly?
----
Reg, G4FGQ

On Fri, 28 May 2004 05:37:07 +0000 (UTC), "Reg Edwards"
wrote:

Richard said -
True, but only insofar as the tuner is adjusted to offer a conjugate.

================================
Richard, how many more times do I have to tell you?

One wonders how many more times indeed, must be love.

You lead people astray.

Jealous?

Or did you make the assertion just to irritate yours truly?

oooooo!

88's
Richard Clark, KB7QHC

Seriously, ducky, do you have any numbers, or is this the Brit version
of foreplay?

Reg Edwards wrote:

Richard said -
True, but only insofar as the tuner is adjusted to offer a conjugate.

Richard, how many more times do I have to tell you? The impedance looking
back into the tuner is NOT the conjugate of the impedance looking into the
transmission line towards the antenna - not even when the tuner is adjusted
for SWR = 1-to-1.

Would you guys please define "conjugate". The following system is matched.
Is there a conjugate in there somewhere? To the right of the match point?

XMTR---50 ohm feedline---x---1/4WL 75 ohm feedline---112.5 ohm load
--
TNX & 73, Cecil http://www.qsl.net/w5dxp



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alhearn wrote:

If you read Chapter 13, "RF Power Amplifiers and Projects", in the 2004
ARRL Handbook, there are pages and pages of discussion of matching
plate or transistor output impedances to 50 ohms output and not once do
they ever refer to output networks dissipating or reflecting reflected
power. Not once. It's always a matter of simply matching one impedance
to another

Sorry, that isn't correct. Maybe the Handbook doesn't emphasize the
point clearly enough, but the design of output networks is specifically
*not* about impedance "matching".

The objective is to *transform* the impedance of the load at the
amplifier's output socket (usually the design value of 50R) into the
correct value of load impedance needed by the amplifier device.

As Al says, the correct value of load impedance for the amplifying
device is the one that will:

provide the highest power output consistent with required linearity,
while staying within the amplifiying device's ratings.


The whole point is to understand that the output network is not trying
to match any particular impedance. It's simply giving the amplifying
device the load impedance it needs in order to function correctly.

Those two objectives are not the same... and understanding the
difference is vital for this whole discussion.


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

alhearn wrote:
If you read Chapter 13, "RF Power Amplifiers and Projects", in the
2004 ARRL Handbook, there are pages and pages of discussion of
matching plate or transistor output impedances to 50 ohms output and
not once do they ever refer to output networks dissipating or
reflecting reflected power.

However, the 15th edition of the ARRL Antenna Book goes into great
detail about how a match point reflects rearward-traveling waves.
If you are designing RF Power Amps, you can simulate load conditions
with lumped components. If you are trying to figure out what happens
on a transmission line (distributed network) you need to take
reflections into account.

Transmission lines have reflections; output matching networks and
tuners don't. The reflections on transmission lines don't make it past
the end of the transmission line -- that's where the reflections take
place. Beyond the end of the transmission line, the reflections are
seen as mere impedances created by standing waves, which are created
by reflections, assuming mismatch.

Impedances created by standing waves are merely V/I ratios, i.e. virtual
impedances. They are the result of standing waves and not the cause of
anything. Physical impedance discontinuities are the cause of reflections
that cause standing waves.
--
73, Cecil http://www.qsl.net/w5dxp



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