Per-Tor,
The tuner (if properly calibrated using a 50 ohm non-reactive load) will
show close to 1:1 SWR at the tuner *input* after a TUNE - it is close
enough that it is practical to assume it is 50 ohms resistive.
After that TUNE, the Lx.xx Cx.xx and NET x ATU menu parameters will
indicate the inductance, capacitance and L network configuration that
were used in the ATU to achieve that match.
Working through the L network impedance transformation using a 50 ohm
input will produce the impedance at the output of the ATU. That will be
the conjugate of the impedance presented in the shack by the feedline.
You are correct that an ATU does *not* alter the VSWR on the feedline -
it is only capable of altering the VSWR at the *input to the tuner to
make the transmitter PA stage "happy" with the 50 ohm ATU input impedance.
I don't think the original poster nor any of the responses made any
inferences that the feedline impedance was being changed.
73,
Don W3FPR
On 7/31/2014 5:29 PM, Per-Tore Aasestrand wrote:
Hi Don,
I still doubt that this is correct.
The L/C values given by the tuner, are the values as seen from the tx side.
It is the values that will make the tx happy. It does not say much about
the impedance at the rig end of the feeder.
In order to change the VSWR on the feeder itself, one has to put the
matching network (tuner) between the antenna and the feeder.
BTW, the tx is probably not conjugate matched by the tuner. Conjugate
matching does not apply to transmitters or power amplifiers. But I realize
there is a huge dissension in this area too. ;-)
Per-Tore / LA7NO
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