[AMPS] Power Meter Readings Question

[Vic Rosenthal]

Jon Ogden wrote:
> 
> I still haven't seen an answer to the question of why I get better PA
> efficiency with the beam than I do with the other two antennas.

First of all, most power meters are very inaccurate when the SWR gets above 2 to
1.  Secondly, an SWR of 2 to 1 means that the antenna impedance is either half
or twice that of the line.  This mismatch causes the current and voltage that
will be seen at the end of the line to vary as the line length is changed.  So,
although the SWR will always be 2 to 1 regardless of the line length, the
impedance seen by the transmitter will vary from too high to too low.

As a result, even if the SWR on the beam is the same as the G5RV, your amp is
possibly seeing very different loads, which it can match more or less
efficiently.

Also, if you have RF flowing on the outside of the coax (possible even with a
balun if the line is closer to one side of an antenna than another), then the
power meter readings can also be further upset.

73,
Vic, K2VCO
Fresno CA

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