[Elecraft] K3: Still unable to set power correctly in, DATA A(sigh)

[Joe Subich, W4TV]

> 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? 

While that might be a solution, it causes other problems. The 
wattmeter is used to measure SWR.  If the wattmeter reads peak 
power in forward it must also be beak reading in reverse in 
order to calculate/display SWR instead of reflected power.  Peak 
reading reflected power makes it difficult for the MCU to adjust 
the tuner (if installed) and makes it nearly impossible to adjust 
while in operation rather than "tune" mode due to the time 
constant of the peak reading circuits.  I don't know of any 
transceiver that combines a peak reading wattmeter with a tuner. 

73, 

   ... Joe, W4TV 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Peter 
> Connors, F5VNB
> Sent: Sunday, January 04, 2009 3:46 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3: Still unable to set power 
> correctly in,DATA A(sigh)
> 
> 
> 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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