On Monday 25 March 2002 14:25, Richard wrote:
> >> Power out on 12 and 17m is around 400W and 30m doesn't really work at
> >> all. The reason for the low output, compared to all of you who
> >> answered (most of you have over 1KW out), I don't know. Are the tubes
> >> tired or do I have too little driving power. The IC-765 only delivers
> >> 90-100W and that, I know, is not enough to drive 2x3-500Z to full
> >> output. The output from the amp is anywhere from 600-900W depending on
> >> band, 10-80M.
> >
> >The factory designed rating for the SB-220 is 1kW INPUT (~600w
> >output) on CW and RTTY, and 2KW PEP on SSB (~1200 watts
> >PEP out) on SSB.
> >
> >Good meters, like the Bird 43, have +-5% of full scale anywhere on
> >the scale tolerance if they are within factory specs. Other meters
> >are generally worse for tolerance. So a 2500w slug in a properly
> >calibrated Bird 43 at 1000 watts true power could read between 875
> >and 1175 watts. People often pretend Bird meters are 0%
> >tolerance, but that is dreaming.
>
> ? Or wishful thinking. Furthermore, the accuracy of any RF wattmeter is
> dependant on the measured resistance of the termination. If a wattmeter
> is calibrated for 50? and the termination is 87?, the wattmeter will
> provide a reading that has no basis in reality.
If the feedline and meter have the same Zo and the sampling system has
sufficient directivity, the meter will show the forward and reflected power
accurately, even if the termination is not Zo. The difference between forward
and reflected power is either heating the feeder or radiated.
Steve
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