"ozgun.harmanci" wrote in message
oups.com...
Hi everybody, I am troubled with transmission line vswr, I hope this is
the right place to ask this question. Is the sr formula same with
unmatched generator? I mean I know that

SWR = ( 1 + |Gamma_Load| ) / ( 1 - |Gamma_Load| )

Gamma_Load is reflection coefficient at load side.

But I think there is a problem with this formula when generator is
unmatched to the transmission line so that there is also a reflection
at generator side. Is that correct or am i making a mistake somewhere?

Why would the generator be "unmatched" in your case is the first question to
ask. However to answer your question I would say no. The logic proceeds as
follows.

Another common formula for calculating SWR is based on measuring the forward
and reflected power from the load.

SWR=(1+sqrt(Pref/Rfwd))/(1-sqrt(Pref/Pfwd))

In the case of a matched generator there is no power reflected from it. In
the mismatched case power is reflected and simply adds to the forward power
from the generator towards the miss matched load. Since the generator is now
miss matched it does not put out full power, it can't by definition of a
conjugally matched generator which can only put out max power in to a
matched load. This extra power is partly absorbed by the load and some is
reflected back toward the generator where it is again reflected back towards
the load. At some point this process of reflections and re-reflections
settles out to a steady state.

http://home.iag.net/~w2du1/Appendix%207.pdf

Look at examples A, B and C diagrams.
http://home.iag.net/~w2du1/Appendix%206.pdf

http://home.iag.net/~w2du1/Chapter%2023.pdf

The power absorbed by the load and what is reflected back is only a function
of the load miss match. The generator miss match only alters the forward
power. The load miss match controls the reflected power towards the
generator, which is always a fixed fraction of the forward power whatever it
maybe. Thus I would say the SWR is not dependent on the generator miss match
to the line, but can the generator miss match can affect the measured
forward power seen on the line. Also when you're measuring the miss match on
the line you are generaly interested in the "load miss match" which as I
stated above is stricly a function of the forward power sent to the load,
and the power reflected from it back towards the generator.


--
Leland C. Scott
KC8LDO

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Thanx in advance.
Arif.