Looking at it another way Bruene was a respected engineer in the military
and non ham commercial world with degree credentials to match. I also had
several email exchanges with him during his spat with Walt Maxwell in QEX,
who BTW, never got out of the 60's with uncalibrated 50-60's test equipment.
JI....nope.
Carl
KM1H
Sent: Wednesday, December 04, 2013 7:14 PM
Subject: Re: [Amps] PARALLEL CAPS IN OUTPUT
This is where life gets interesting.......
About ten or twelve years back, there was a big argument about whether you
should have a conjugate match between PA and load. Argument one was that
Thevenin demanded a conjugate match for optimum power transfer. Argument
two (Warren Bruene, W5OLB) was that the tx should have the lowest possible
output impedance for maximum efficiency. Now I incline to Bruene's
approach. W8JI was for Thevenin. Experiments showed that linear PAs showed
maximum linear output when there was a Thevenin match, but if you did the
usual sums on PAs, you saw that that the efficiency was around 50% - which
you expect - and thus the Thevenin match gave much the same answer. As
soon as you applied it to Class C, you no longer had a linear system and
the Thevenin match camp claimed it was no longer valid. This is as maybe,
but seems to me to have some definite legitimacy as an argument.
So the impedance looking back into a correctly tuned linear amplifier,
whether you believe W5OLB or W8JI, actually ends up about the same - not
that far off 50 or whatever ohms.
So the reflection back from the tx to the antenna is pretty small.......
Obviously a bit different with a Class C pa, but not that much......
So I think multiple reflections can be discounted, at least for correctly
tuned amplifiers and PAs.
73
Peter G3RZP
========================================
Message Received: Dec 04 2013, 11:33 PM
From: "Bill Turner" <dezrat1242@wildblue.net>
To: "Amps" <amps@contesting.com>
Cc:
Subject: Re: [Amps] PARALLEL CAPS IN OUTPUT
ORIGINAL MESSAGE: (may be snipped)
On Thu, 05 Dec 2013 00:08:34 +0100, Peter wrote:
>the argument used by all the authorities is this:
>
>At an open circuit the forward voltage is Vf. Because it is reflected as
VR and is the same voltage - necessarily - the two voltages add to give a
reflected voltage of 2Vf. To get more requires energy to be made.
>
>So on a loss less line, the only voltage reflected back to the tx is
>2Vf - where
Vf is the rms volts that would appear at the load when the line is
matched.
REPLY:
But in an open circuit, isn't the reflected voltage reflected again? And
again and again? The only thing that keeps it from increasing forever is
loss in the line, I would think.
Can't prove it, but it seems logical.
73, Bill W6WRT
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