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Old March 5th 06, 03:29 AM posted to rec.radio.amateur.antenna
Reg Edwards
 
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Default Reflection Loss

I have just had several glasses of Australian Zonte's Footstep wine.
I can recommend it. Its name can be traced back to a marsupial which
replaced the dinosaurs.

Transmission lines, which even the dinosaurs knew nothing about, are
associated with losses of one sort and another. But there is one sort
of loss which is never mentioned in discussions on this newsgroup. It
is reflection loss.

Reflection loss is sometimes known as mismatch loss.

It is that loss which occurs in the load impedance because it is not
matched to the line impedance Zo. When the line is not matched there
is a reflection of amps and volts back towards the generator.

The reflected volts and amps, in conjunction with the existing volts
and amps, present to the generator an impedance which causes it to
deliver to the line exactly the power in the load plus the power lost
in the line. That this occurs is quite obvious.

When calculated, the power lost in the line automatically takes into
account the increase in loss due to SWR which occurs on the line due
to the mismatch of the load.

But the most important parameter is not the SWR but the reflection
coefficient, Gamma.

Gamma = ( Zt - Zo ) / ( Zt + Zo ).

The loss in the load due to reflection is given by

Reflection Loss = 4.343 * Ln( 1 - Square( G ) ) decibels.

where G is the magnitude of the reflection coefficient which is easy
to measure.
----
Reg.


 
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