R: [AMPS] Power Meter Readings Question

[Maurizio Panicara]

SWR changes, in connection to line lenght changes, when the antenna
impedance is different than that of the line and the generator.

According to the transformation property of the lines, when the load
(antenna) impedance differs from the line impedance, there is an impedance
transformation that's related to the antenna impedance, to the line
impedance and to the line lenght.
The only case where this does not apply, is when the line is exactly an half
wavelenght or multiples.  In this last case, the load impedance appears to
the generator end of the line as is, independently by the line impedance.
In the area of critical line lenghts ( typical the quarter wave case & odd
multiples) and mismatched antennas, including those due to reactive
components (read too short or too long antennas), a slight line lenght
variation can easily produce consistent SWR changes and power readings.

It's obvious that a 50 Ohm wattmeter, unless derived by a thermocouple,
doesn't indicate a real power if the load ( as seen through the line or an
antenna tuner ) is largely reactive, or even resistive, but away of the
nominal
value.

73,
Mauri I4JMY

i4jmy@iol.it


-----Messaggio originale-----
Da: Peter Chadwick <Peter_Chadwick@mitel.com>
A: 'amps' <amps@contesting.com>
Data: mercoledì 28 aprile 1999 17.12
Oggetto: RE: [AMPS] Power Meter Readings Question


>If changing the length of line changes the SWR, it's usually a sign of RF
on
>the outside of the line.
>
>73
>
>Peter G3RZP
>






















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