On Fri, 25 Feb 2005 03:17:12 GMT, gwhite wrote:

RF transmitter power amps are
not "impedance matched." Neither are audio power amps for that matter.

Hi OM,

You seem to be shy of facts and long on claims. Got any experience at
the bench, or is this all arm-chair philosophy?

73's
Richard Clark, KB7QHC

Arguments about whether the power ammplifier is matched or not matched to 50
ohms arise due to misunderstandings about the meaning of "matched".

Meaning 1.
-------------
The PA has been designed for maximum, linear, undistorted power output when
loaded with Ro ohms and the load reistance has actually been adjusted to
equal Ro. Ro is usually 50 ohms. (There may be additional criteria to
define what constitutes an optimum match.)

Meaning 2.
-------------
The load impedance Z = R+jX has been adjusted to equal the conjugate of the
internal impedance resistance of the PA. (The internal impedance of the PA
is usually unknown but the circuit is assumed to behave as if a conjugate
match exists.)

The two meanings are entirely different from each other. If there is danger
of confusion then the meaning should be stated. Some people already use the
descriptions "Zo match" and "Conjugate match".
----
Reg, G4FGQ

In article ,
Reg Edwards g4fgq,regp@ZZZbtinternet,com wrote:
Arguments about whether the power ammplifier is matched or not matched to 50
ohms arise due to misunderstandings about the meaning of "matched".

Meaning 1.
-------------
The PA has been designed for maximum, linear, undistorted power output when
loaded with Ro ohms and the load reistance has actually been adjusted to
equal Ro. Ro is usually 50 ohms. (There may be additional criteria to
define what constitutes an optimum match.)

Meaning 2.
-------------
The load impedance Z = R+jX has been adjusted to equal the conjugate of the
internal impedance resistance of the PA. (The internal impedance of the PA
is usually unknown but the circuit is assumed to behave as if a conjugate
match exists.)

Meaning 3:
The PA has been designed to deliver the maximum power at that load
impedance and the distortion is not an issue.


The two meanings are entirely different from each other. If there is danger
of confusion then the meaning should be stated. Some people already use the
descriptions "Zo match" and "Conjugate match".

Actually meanings 2 and 3 are effectively equal in the case of the tuned
system, if you define the Zo based on the change in output power vs
connected impedance for small changes. Since a lot of such systems aren't
linear, this is the way you end up having to define the impedance. You
can't use open circuit voltage and short circuit current.

Remember that this all started with the OP having a "transmitter". This
would include any needed filtering. He was just connecting a 1/4 and 1/2
wave lengths of bent up wire. His output filter, I assume is just a bunch
of LC sections.



--
--
forging knowledge

The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

The correct description is "internal impedance" or "internal resistance" and
should always be used.
----
Reg.

"Reg Edwards" wrote in
message ...
The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

I suppose the same could be said of any block that is
susceptible to having some feedback put around it.
Therefore the term "output impedance" should never
be used at all. And of course, any term that could, or
has ever been known to lead to an argument, with any
uninformed person that might come along, should be
eliminated from our vocabulary.

Uuugh. Mmmmph. Me drag woman to cave by hair.

The correct description is "internal impedance" or "internal resistance" and
should always be used.

Nonsense.

If I wanted to speak of an impedance inside of some
circuit, I might loosely speak of it as "internal", but in
any useful discussion, it would be spoken of as either
an output impedance or an input impedance, and, with
most people I have such discussions with, there would
be no need to add that some unknown additional feed-
back not part of the present discussion could alter the
observable impedance.

I hope your post was a troll.

--
--Larry Brasfield
email:
Above views may belong only to me.

I read in sci.electronics.design that Larry Brasfield donotspam_larry_b
wrote (in )
about 'Say what you mean.', on Fri, 25 Feb 2005:

If I wanted to speak of an impedance inside of some circuit, I might
loosely speak of it as "internal", but in any useful discussion, it
would be spoken of as either an output impedance or an input impedance,

The problem is that people say 'output impedance' when they mean 'load
impedance'. To prevent misunderstanding I use the term 'output source
impedance'.

There are also some people who use 'input impedance' when they mean
'source impedance'. I don't talk to them. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

John Woodgate wrote:
"The problem is that people say "output impedance" when they mean "load
impedance".

Quite right. I`ll use "source" and "load".

Current through a load depends on the voltage. Ratio of volts to amps is
the impedance. A source with the same resistance and offsetting
reactance to the load enjoys a Goldilocks relationship with its load.
The source`s volts and amps perfectly match the demands of the load.
It`s just right. There`s no surplus of either volts or amps when source
and load are connected. Its a match. Only a matched source and load
deliver all the power available in a source.

If we have too much resistance in our load, it doesn`t take as much
power as it could.

If we have too little resistance in our load, too much power is lost in
our source.

The perfect match of equal source and load resistances, with the
reactance neutralized, is the only condition permitting maximum power
transfer.

Somme amateurs want all the power they can get from their transmitters.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Some amateurs want all the power they can get from their transmitters.

I learned long ago that approach burns up unprotected
transmitters. Nowadays, I settle for efficiency and
lots of protection circuitry.
--
73, Cecil http://www.qsl.net/w5dxp

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True, but only in a linear system representable by a Thevenin source having
a resistive component that is dissipative. But an r-f amplifier is a
non-linear system with a non-dissipationless "internal resistance" and
cannot be modeled with a Thevinin dissipative source.

IF the Thevenin source approach worked, we would have to be content with max
50% efficient amplifiers. We know we can do better than that substantially.

The latest QEX has a revealing examination of impedance and conjugate
matching matters.

Bottom line seems to be that one concentrates upon the specific load
*resistance* specified for all other specs to be met. Such a load permits
the amplifier to deliver maximum power within specifications and as such is
conjugately matched to its load.


--
73, George W5YR
Fairview, TX

http://www.w5yr.com




"Richard Harrison" wrote in message
...
John Woodgate wrote:
"The problem is that people say "output impedance" when they mean "load
impedance".

Quite right. I`ll use "source" and "load".

Current through a load depends on the voltage. Ratio of volts to amps is
the impedance. A source with the same resistance and offsetting
reactance to the load enjoys a Goldilocks relationship with its load.
The source`s volts and amps perfectly match the demands of the load.
It`s just right. There`s no surplus of either volts or amps when source
and load are connected. Its a match. Only a matched source and load
deliver all the power available in a source.

If we have too much resistance in our load, it doesn`t take as much
power as it could.

If we have too little resistance in our load, too much power is lost in
our source.

The perfect match of equal source and load resistances, with the
reactance neutralized, is the only condition permitting maximum power
transfer.

Somme amateurs want all the power they can get from their transmitters.

Best regards, Richard Harrison, KB5WZI

On Fri, 25 Feb 2005 21:42:37 -0800, Larry Brasfield wrote:

Uuugh. Mmmmph. Me drag woman to cave by hair.

Uh. Nuh. Drag _FROM_ hair.