[AMPS] Conjugate Matching In Class B and C Amplifiers
Sat, 12 May 2001 14:49:05 -0700
>It's interesting to note (and rightfully so) that space has been given to
>Walt in a League publication. Could they possibly believe there may be some
>truth in what he's been advocating all along?
€ About 10-yrs. ago, a QST staffer told me that they stopped publishing
W. Maxwell's conjugate-matching info because of the discrepancy with
>----- Original Message -----
>From: "Tom Rauch" <email@example.com>
>To: "Phil Clements" <firstname.lastname@example.org>; "AMPS" <email@example.com>; "Jon
>Sent: Friday, May 11, 2001 20:38 PM
>Subject: Re: [AMPS] Conjugate Matching In Class B and C Amplifiers
>> > > As I understand it, Mr. Maxwell asserts that linear amplifiers are
>> > > conjugately matched. If this is true, the efficiency could not
>> > > exceed 50%.
>> > OK. You are correct Rich. If conjugate match occurs, then an equal
>> > amount of power is absorbed by both source and load - hence the 50%
>> > efficiency.
>> That is not correct, although it has crept into recent texts. I think
>> that concept comes from taking a Thevenin model literally, as an
>> actual circuit with a dissipative resistance in series with a source.
>> It's unfortunate that electrical engineers used the same term
>> (resistance) to describe the ratio of across-to-through vectors as
>> we use to describe the characteristics of a resistor.
>> Even more unfortunate, we now are assuming a Thevenin model is
>> actually the real world system with a dissipative resistance.
>> I did load pulls on class C PA's with more than 70% efficiency, and
>> the load-pull indicated a conjugate match (50 ohm source) when
>> efficiency was maximum. There is nothing that says PA's must be
>> operated at a conjugate match, just like there is nothing that says
>> efficiency is only 50% when the PA is conjugately matched.
>> It isn't that difficult to measure a PA and prove this, yet most
>> people spend far more time arguing than measuring.
>> 73, Tom W8JI
- Rich..., 805.386.3734, www.vcnet.com/measures.
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