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From: Larry Benko <>
Date: Wed, 04 Dec 2013 18:37:43 -0700
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Multiple reflections in the data world are very easy to see with a TDR. They do exist and the only thing to keep them from going on forever is the reflection coefficient at both ends and the loss in the transmission line. A pulse generator, some length of twisted pair or coax with delay long compared to the data bit time, and a dual channel storage scope will clearly show them. Again this stuff is well known by competent engineers.

I am not going to engage in the conjugate match war. Non-linear circuits are harder to analyze but not that hard.

Larry, W0QE

On 12/4/2013 5:14 PM, peter chadwick wrote:
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you no longer had a linear system and the Thevenin match camp claimed it was no 
longer valid.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.


Peter G3RZP

  Message Received: Dec 04 2013, 11:33 PM
  From: "Bill Turner" <>
  To: "Amps" <>
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 - 
  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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