[Amps] Mismatch loss

Gary Schafer garyschafer at comcast.net
Thu May 3 16:47:47 PDT 2012

"Mismatch loss" may or may not cause a system loss. It depends on the

As I stated in a previous post if there is no re-reflection (conjugate
match) at the generator then mismatch loss will be realized the full amount.
It is a real loss.

If you look at a transmitter that has an isolator on its output (typical of
UHF/VHF), any reflected power back toward the transmitter will not be
re-reflected to the load/antenna but will be absorbed in the isolators load.
So if your load/antenna or connector presented a 3:1 swr there would be 25%
reflected power. All of that reflected power would be lost in the isolators
load. A 100 watt transmitter would only provide 75 watts to the

The same thing happens on the test bench as most signal generators provide a
resistive source and there is never a conjugate match. Any reflected power
from the load gets absorbed in the source and does not get re-reflected back
to the load. 
Any mismatch in impedance results in loss. This is where the term mismatch
loss comes from. The mismatch can be the result of a connector that presents
a different impedance than Zo or it can be from the load that is not the
same impedance as Zo.
In other words any SWR will cause a loss of power reaching the load with
this type of generator. No transmission line required.

But with a typical transmitter with a tuner at its output that same 3:1 swr
load will receive most all of the 100 watts due to the tuner compensating
for the mismatch back at the transmitter. It will provide a conjugate match
and most all of any reflected power will be re-reflected back to the load.
In this case the only system loss will be that of the transmission line loss
with no SWR plus any additional loss in the line by the reflected power
running back and forth on the line.

Gary K4FMX

> What you're calling "mismatch loss" is NOT loss, it is nothing more than
> the impedance transformation that occurs in any mis-matched line.  The
> only signal LOST is that due to excess attenuation.  What you're calling
> "mismatch loss" is entirely the result of where along the line the
> signal is sampled or retrieved, and the "mismatch loss" can be
> eliminated either by changing the line length or transforming the
> impedance.

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