[TowerTalk] Reflections, Tuners and Antenna Forum Talks

[Tom Rauch]

Hi Mike,

I swore I wasn't going to get into one of these threads, but...
>
> transmission line transformer. The drawing shows how the multiple
> reflections of the incident energy add up to form the steady state
> solution for the 1/4 wave line (matched condition). The following page
> shows the time progression for a short pulse along the same 1/4 wave line.
> Kraus states "It is clear that the transformer fails to function as a
> reflectionless device for a pulse as short as indicated.........".

I'm not sure where any of you are going with this stuff.

It's true you can't consider the system in a steady state condition 
with a wide-bandwidth very fast rise-time transmission, but we sure 
can with a narrow-band signal like one of our HF transmitters, 
especially with the length of transmission lines we deal with. The 
rise time is very slow, it takes many many RF cycles to build 
power no matter what operating or mode frequency we are using.

There is nothing I can find where Maxwell claims a system is 
matched under transient conditions, and if I follow his reasoning it 
is obvious the system would not be matched under transient 
conditions. As you say that is why television transmitters, or any 
other system having fast information rate changes compared to the 
delay in the transmission line, requires a nearly perfect VSWR.

So I say, big deal. Wave mechanics work just fine. They ALSO 
explain why high load VSWR isn't acceptable in a system where 
the time delay in the transmission line approaches the information 
rate change in the transmitter.


73, Tom W8JI
w8ji@contesting.com

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