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Old December 25th 05, 12:35 AM posted to rec.radio.amateur.antenna
 
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Default Shorting out a transmission line

On Sat, 24 Dec 2005 15:40:25 -0800, Roy Lewallen
wrote:

wrote:
I leave only this.

At VHF and up it's common to use a shorted 1/4 wave section for
second harmonic suppression at the output. Very effective and dirt
cheap. The finals are not the least bit bothered.

If a short appeared near a 1/4 wave node at operating frequency
it might go unnoticed.


I'm afraid it wouldn't go unnoticed. The transmitter would see an open
circuit, instead of the proper load of typically 50 ohms. The effect on
the transmitter would be the same as disconnecting the feedline at the
transmitter.

Roy Lewallen, W7EL


I did use the word "might" rather than will.

Actually it depends on the real life characteristics of the short. If
it were a perfect short (in theory) yes. But if there is any varience
from that it's going to be harder to predict. Likely it world look
more like a higher impedence, but not completely. In all likelyhood
the parameter that needs to be know more than any one
its frequency. At 432 it's impact would be very different than say
7.2mhz.



Allison