[TowerTalk] Perpetum Mobile

Bill Coleman aa4lr@arrl.net
Wed, 19 Dec 2001 10:37:05 -0500

On 12/12/01 11:19 AM, Mike at W4EF@dellroy.com wrote:

>Alex brings up a good question. When using an antenna tuner driving
>a long feedline, what does my final amplifier see during the transient
>response while the energy is sloshing back and forth between the
>antenna and the tuner setting up the steady state match conditions?
>For a short time (before the reflection from the antenna has time works
>its way back to the tuner), the tuner will see the surge impedance of
>the  transmission line which will be transformed by the matching
>network into an impedance that is most likely not 50 ohms. For a very
>short time, the finals might see a very bad mismatch.

How long is your feedline? 

Given that your transmitter doesn't come up to full power (on CW) for 
about 1-2 ms, the electrical current can travel about 200-400 km in that 
time. (Assuming .66 velocity factor in the feedline).

I think you need to worry about feedline losses more than any "sloshing" 
effect of having complex impedances on the feedline....

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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