[TowerTalk] Perpetum Mobile
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: email@example.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
AN Wireless Self Supporting Towers are now available! Windloading tables,
foundation diagrams and charts, along with full details are now at the
AN Wireless Web site: http://www.ANWireless.com
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Administrative requests: towertalk-REQUEST@contesting.com