[TowerTalk] Walt Maxwell responds to Steve Best

[Tom Rauch]

> W2DU:
> 
> The impedance one measures looking
> back into the matching device is entirely different from
> the impedance seen by waves reflected from a
> mismatched line termination on reaching the matching
> device when the forward waves from the source are
> present simultaneously. This is one of the many points
> Steve fails to understand, even after I've tried to explain
> to him with no success.
> 
> Steve's Response:
> 
> The impedance a traveling wave sees at the end of a transmission line does
> not change because of the presence of source voltage.  

Walt is correct Steve.

You can not ignore the fact the source is supplying energy, no 
matter how much you want to.

Shutting off the generator and measuring the impedance looking 
BACK into the source does NOT indicate the impedance a 
reflected wave sees.

Let me give an example. Yesterday I did a load-pull on a 
transmitter. The source impedance, when the transmitter was 
tuned to provide maximum energy transfer to a 50 ohm load, was 
50 ohms. I found that impedance by slightly perturbing the load and 
measuring delta E and delta I at both 50 and 48 ohms, and 
calculating the impedance by delta E over delta I.

I reduced power to 1/100th of the initial power, and the source 
impedance remained 50 ohms.

But when I "pinged" the source externally with no output from the 
source, the impedance was nowhere near 50 ohms.

I have made hundreds of measurements, and haven't found 
anything that flys in the face of what Maxwell wrote.  

I also have not found anything that agrees with your theory. When 
measurements agree with your theory, and disagree with Walt, 
then I will quickly change my opinion.
73, Tom W8JI
w8ji@contesting.com

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