[Elecraft] Re: K3 - 'Unwanted' TX Gain calibrations?

[wayne burdick]

Hi Paul,

>> Been wondering just how the TX Gain calibration works. To quote from 
>> the
>> manual - "The gain constant is updated whenever the TUNE function is 
>> activated on a given band at one of three specific power levels: 
>> 5.0W, 50W, and 1.00 milliwatt."
>
> To Stewart's point, does the gain of the K3 recalibrate every time 
> TUNE is depressed at one of the three stated power levels... ?

Yes. It doesn't matter whether you select one of these power levels 
manually using the PWR knob, or using the TUN PWR menu entry. It will 
always recalibrate the gain constant during TUNE if you happen to be at 
one of these power levels.

However, it will only do this if the SWR is 2.0:1 or less. This 
provides plenty of safety margin.

> Finally, what prevents the re-loading of new gain data if as Stewart 
> suggest, he sets the K3 power to exactly 5 watts or 50-watts and 
> depresses TUNE for external ATU tuning purposes?  Should he instead 
> stay away from those two values and use perhaps 49 or 51 watts?

No need to do this. The fact that it recalibrates every time you do 
TUNE at one of these levels is not a problem. It just updates the 
EEPROM constant if it has changed.

The TX gain constant is only there to compensate for small per-band 
gain variation within the K3's transmitter. If you've done the power 
calibration, then you can set PWR and be fairly close to the target 
level on each band. Thus the MCU won't have to adjust power very much 
in real time. In CW mode, this means we can apply our keying waveform 
open-loop, preserving the target raised-cosine shape at all power 
levels. In voice modes it helps achieve our goal of applying a minimum 
of ALC.

73,
Wayne
N6KR


---

http://www.elecraft.com