Ken Smith wrote:


RF transmitter power amps are certainly "impedance matched" to the
intended load.

I'm sorry, but they are not. Nor are any power amps that I know of. Efficiency
(and thus necessarily output swing) is what matters for power amps. To maximize
swing requires load line matching, not impedance matching.

If you want to study RF PA's I suppose Cripps is one of the best I know of for a
modern text:

http://www.amazon.com/exec/obidos/tg.../-/0890069891/

In article , gwhite wrote:
Ken Smith wrote:


RF transmitter power amps are certainly "impedance matched" to the
intended load.

I'm sorry, but they are not. Nor are any power amps that I know of. Efficiency
(and thus necessarily output swing) is what matters for power amps. To maximize
swing requires load line matching, not impedance matching.

I still say they are. Motorola AN-721 takes on the theory. AN-758 does a
practical example matching 12.5 Ohms into 50 Ohms


--
--
forging knowledge

Ken Smith wrote:

In article , gwhite wrote:

Ken Smith wrote:

RF transmitter power amps are certainly "impedance matched" to the
intended load.

I'm sorry, but they are not. Nor are any power amps that I know of. Efficiency
(and thus necessarily output swing) is what matters for power amps. To maximize
swing requires load line matching, not impedance matching.


I still say they are. Motorola AN-721 takes on the theory. AN-758 does a
practical example matching 12.5 Ohms into 50 Ohms



Sure are. A 30 year ago 500 level course I took called Non-Linear
Transistor Design said so. The way you handle class C etc. is by
handling each harmonic separately in your analysis of the transistor
plus tank circuit. You match to the harmonic you want. It may be the
fundamental, or the third for a tripler, etc.

tom
K0TAR

On Sat, 26 Feb 2005 00:40:09 +0000, Ken Smith wrote:

In article , gwhite wrote:
Ken Smith wrote:


RF transmitter power amps are certainly "impedance matched" to the
intended load.

I'm sorry, but they are not. Nor are any power amps that I know of. Efficiency
(and thus necessarily output swing) is what matters for power amps. To maximize
swing requires load line matching, not impedance matching.

I still say they are. Motorola AN-721 takes on the theory. AN-758 does a
practical example matching 12.5 Ohms into 50 Ohms



Evidently, the guy's never tuned up a 40 meter pi-net output transmitter. ;-)

If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

Cheers!
Rich

Rich Grise wrote:
Evidently, the guy's never tuned up a 40 meter pi-net output transmitter. ;-)

If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.
--
73, Cecil http://www.qsl.net/w5dxp


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On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
Evidently, the guy's never tuned up a 40 meter pi-net output transmitter. ;-)

If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Thanks,
Rich

Rich Grise wrote:

On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.
--
73, Cecil http://www.qsl.net/w5dxp


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On Sat, 26 Feb 2005 08:33:25 -0600, Cecil Moore wrote:

Rich Grise wrote:

On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.

No, just trying to make the point that it does, in fact, _have_ an
impedance. (even if it's running class E.) What that exact impedance is,
of course, is left as an exercise for the reader. :-)

And another thing - in a transmitter, the impedance matching only happens
at the one frequency, which is a lot different scenario from, say, a
stereo. This could be a confusion factor here.

Thanks,
Rich

Cecil Moore wrote:

Rich Grise wrote:
Evidently, the guy's never tuned up a 40 meter pi-net output transmitter. ;-)

If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Exactly. Pure coincidence.

Ken Smith wrote:
"Motorola AN-721 takes on the theory. AN-758 gives a practical example
matching 12.5 Ohms into 50 Ohms."

As King, Mimno, and Wing said, a conjugate match is required to get
maximum power out of the radio.

Terman says the same on page 76 of his 1955 edition of "Electronic and
Radio Engineering."

There is also an Eimac application note on matching their tubes to a
load on the final amplifier.

If Larry, Moe, and Curly published an application note, we`d have a
crowd of skeptics here. See Terman`s Fig. 3-21 on page 77 of his 1955
edition.

Best regards, Richard Harrison, KB5WZI