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

[Joe Subich, W4TV]

> If the onboard meter _thought_ the K3 was making the requested 
> power, that would be one thing.  But in this case the onboard 
> meter thinks it's putting out 2x the power, which it is.

It depends on what part of the system thinks what.  In this 
case the MCU is reading a given value but interpreting it 
as something else thanks to TXG VCE.  

TXG VCE does not effect the peak power in SSB or AFSK A with 
single tone modulation.  It does effect peak power in DATA A. 

If you are seeing about 2x the power called for, decrease 
TXG VCE by 3 dB and see if the situation does not resolve 
itself (at the expense of power output in USB/LSB).  Although 
the wattmeter is peak reading according to Wayne, TXG VCE 
still provides an inappropriate "adjustment." 

73, 

   ... Joe, W4TV 
 
 



> -----Original Message-----
> From: Steve Ward [mailto:stevewa at spiritone.com] 
> Sent: Monday, January 05, 2009 3:38 AM
> To: lists at subich.com
> Subject: Re: [Elecraft] K3: Still unable to set power 
> correctly in, DATA A(sigh)
> 
> 
> Joe,
> 
> If the onboard meter _thought_ the K3 was making the requested power, 
> that would be one thing.  But in this case the onboard meter 
> thinks it's 
> putting out 2x the power, which it is.  So, I dial in 40w and 
> I get 80w 
> both by the internal meter and by my admittedly less than lab-quality 
> MFJ dummy load+meter.
> 
> It did not do this before the most recent firmware.  
> Something got broken...
> 
> 73,
> 
> Steve AD7OG
> 
> Joe Subich, W4TV wrote:
> >   
> >> The point is it was providing the correct power output levels
> >> before the last couple of firmware revisions.  Something 
> >> changed that made it go from putting out approximately the 
> >> right power level, to putting out WAY TOO MUCH (i.e. causing 
> >> splatter) power.
> >>     
> >
> > Not true ... in spite of careful calibration at both 5 and 50
> > watt levels neither of my K3s has ever produced exactly the 
> > power requested on any band other than 20 meters, on any mode 
> > other than CW and at any power other than 5 or 50 watts.  The 
> > variations can be as much as 3 dB on SSB depending on the peak 
> > to average ratio of the driving audio and amount of compression 
> > used.  
> >
> > 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
> >  
> >
> >
> >
> >   
> >> -----Original Message-----
> >> From: elecraft-bounces at mailman.qth.net
> >> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Steve Ward
> >> Sent: Saturday, January 03, 2009 2:54 PM
> >> To: elecraft at mailman.qth.net
> >> Subject: [Elecraft] K3: Still unable to set power correctly 
> >> in, DATA A(sigh)
> >>
> >>
> >> "Joe Subich, W4TV" Wrote:
> >>
> >>     
> >>> So?  Reduce the power you request to get the required 
> output. What 
> >>> other radio has a "calibrated" power output control?
> >>>       
> >>> The wattmeter in the K3 is relative ... there is a 
> documented power 
> >>> vs. frequency slope.  Testing seems to indicate there are also 
> >>> nonlinearities with changes in peak to average ratio and as the 
> >>> power level moves away from the calibration points. The 
> directional 
> >>> coupler in the K3 does not have the high level of directivity and 
> >>> compensation of a product like the Telepost LP-100 nor 
> does it have 
> >>> the high quality detectors.
> >>>       
> >>> If you want a bloody laboratory grade meter, buy a 
> laboratory grade 
> >>> power meter.
> >>>       
> >> The point is it was providing the correct power output levels
> >> before the last couple of firmware revisions.  Something 
> >> changed that made it go from putting out approximately the 
> >> right power level, to putting out WAY TOO MUCH (i.e. causing 
> >> splatter) power.
> >>
> >> Setting TXG VCE to -3 dB gets DATA A output almost to where
> >> it should be, but of course adversely affects SSB.
> >>
> >> This is NOT about the accuracy of the wattmeter, its about
> >> overdriving the PA.
> >>
> >> 73,
> >> Steve
> >> AD7OG
> >> K3 #1544
> >>