[Elecraft] K3 Beta firmware rev. 2.82

[Julian, G4ILO]

Joe Subich, W4TV-4 wrote:
> 
> 
> You CAN NOT make those tests at 50 Watts!  The power calibration 
> circuitry will be constantly changing the internal gain.  If 
> the ATU is enabled and/or your dummy load is not flat the changes 
> invalidate the measurements. 
> 

Why on earth not? I think you are confusing the situation with what happens
when you press TUNE at 50 watts (which I personally think is a disaster that
has already happened on many occasions, but that is another matter.) If you
are suggesting that you cannot use the K3 AT ALL with the power set to 50
watts then something is deeply wrong, either with your understanding or with
the design of the radio.



> 
> Further, single tone power calibration is only accurate for 
> the specific frequency within the IF filter on which the 
> calibration is performed.  If I calibrate power in CW mode 
> that calibration point is approximately 300 Hz from one 
> "corner" of the 2.8 KHz filter thanks to the way the K3 
> offsets the filters.  When I switch to DATA A, and try to 
> test the power level with a 1500 Hz tone, I can see 2 dB more 
> power simply because my 2.8 KHz filter has a 4 dB slope across 
> the passband and the K3 gain calculation includes compensation 
> for the loss at the calibration frequency.  If I check the 
> power with a 1 KHz tone, the difference may be 3 dB (DATA A 
> is USB, CW calibration is LSB so the slope changes direction 
> with tone).  If I switch to AFSK A (REV to stay with USB) 
> and check power with a 2295 Hz (USB Mark) tone, the difference 
> may be down to one dB or so.  
> 

Well I may not be a professional radio engineer but I am not dumb enough to
try testing with different frequency tones. As stated, I was testing with
the same tone in SSB and DATA mode. As far as I am aware, the filter
passband on transmit is the same in both modes. Even if not, this does not
explain why I got 65W on most bands and 20W on 30m, with exactly the same
input.



> 
> There are too many uncompensated variables to expect the K3 
> to maintain absolute control over the power output with 
> changing antennas, power levels, modes, (relative) frequency 
> within the IF passband and possibly even different filters. 
> ALC controls the audio level into, and the RF level out of 
> the DSP (modulator) process - it is an ALC (automatic LEVEL 
> control) NOT an APC (automatic POWER control).  
> 
> The ALC is an open loop system - the loop gain is calibrated 
> once at the 5 watt level and once at the 50 watt level for 
> one specific frequency in the IF passband.  Once that is 
> done, ALC simply controls the DSP gain.  If you change the 
> system gain following the DSP, the output power level WILL 
> CHANGE.  I'm sure it would be theoretically possible to 
> calibrate the system gain from 100 Hz to 2900 Hz offsets 
> from the carrier (for both the USB and LSB cases) and apply 
> that mask to the modulation process but does the DSP system 
> have enough horsepower to do so and is it worthwhile simply 
> so the operator can avoid the need to check his power level 
> when changing mode or modulating frequency? 
> 
> 

Sorry, but I don't see where the system gain comes in to the argument, since
I am reporting results with the same frequency tone used at all times. Nor
do I see why changing antennas has any relevance to this issue, since I am
using a dummy load that is flat to 500MHz for these tests.

The K3 is perfectly capable of regulating the power to a level of accuracy
that is acceptable to me in SSB mode. All I am asking is that it perform the
same task in DATA A, which is just SSB after all. Early versions of the
firmware were perfectly capable of doing this. Why am I being treated as if
I am demanding the impossible for simply asking for something that can be
done and has been done.

I really am very, very fed up with the K3 at this point in time.

-----
Julian, G4ILO. K2 #392  K3 #222.
http://www.g4ilo.com/ G4ILO's Shack   http://www.g4ilo.com/blog.html G4ILO's
Blog    http://www.g4ilo.com/kcomm.html KComm for Elecraft K2 and K3 
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