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

[Joe Subich, W4TV]

Wayne, 

> 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.

Does the K3 include a "wattmeter slope" adjustment?  If so, I can't 
find it.  

When the wattmeter is calibrated on 20 meters, I find a .75 to 1 dB 
slope between 1.8 and 50 MHz when compared with both my LP-100 and 
Bird wattmeters (power is about .25 dB high on 160 and a bit more 
than .5 dB low on 50 MHz).  The slope appears to be consistent at 
both 5 and 50 watts. 

If a slope adjustment is not available, it might be worthwhile to 
add the option to calibrate the wattmeter at two (160/10 or 160/6) 
or three points (160/20/6) for frequency compensation. 

73, 

   ... Joe, W4TV 
 




> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of wayne burdick
> Sent: Tuesday, September 23, 2008 4:42 PM
> To: Elecraft Reflector
> Subject: [Elecraft] Re: K3 - 'Unwanted' TX Gain calibrations?
> 
> 
> 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
>