Joe
Thank you for pointing out the difficulties in setting average power
across a range of modulation types.
Whatever the peak/average ratio of the modulation, the output power from
the PA is peak limited - so wouldn't the answer be a K3 power meter and
power control that shows/sets peak rather than average power? The power
control would then be set just once and the average power would be an
unavoidable consequence of the choice of modulation.
73, Pete F5VNB
Joe Subich, W4TV wrote:
Setting a power control calibrated for CW and expecting that
level to be accurate for PSK31 or any other arbitrary digital
modulation is complete folly and utter hubris. Among other
issues the wattmeter does not know if you are setting peak
or average power and it does not know what the average power
should be for the arbitrary data and arbitrary modulation.
For the K3 to accurately control the power level in all modes
the its directional coupler would probably need to be improved
by at least an order or magnitude. The response flatness would
need to be improved by at least an octave and the detectors would
need to be substantially more linear ... and that's just for CW.
To handle arbitrary audio inputs takes some knowledge of the
peak to average ratio as well as the peak duration (duty cycle)
in order to select the proper detector time constants. Every
voice every digital mode and every arbitrary data stream will
have different peak to average ratios and duty cycles. Do you
expect the DSP to calculate those values on the fly? Perhaps
the power metering should be derived from a DSP based spectrum
analyzer?
Accept the fact that the power level control is relative. If
Wayne and Lyle can improve on it that's great. However, trying
to hold .1 dB or even 1 dB accuracy from 1 mW to 120 W, 1.8 MHz
to 54 MHz with arbitrary modulation sources in a reasonably
priced amateur transceiver is a fool's errand.
73,
... Joe, W4TV
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