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

[Paul Christensen]

Wayne,

Ahhh...I think I see now.  In effect, it's really an ALC loop gain 
calibration, with ALC gain optimized for each band -- correct?  This sounds 
very similar to what Ten Tec is using with their Omni VII, only their 
calibration is conducted once at the factory to achieve optimum band-by-band 
ALC gain.  Their rig also nicely preserves the raised-cosine CW waveform at 
all power levels.

For some reason, I had this thought in my head that forward gain between say 
the driver stage and PA was being changed in the firmware, irrespective of 
the ALC.  Perhaps it was the "TX Gain" nomenclature...

Also, after the TX Gain calibration, I am seeing about 75-80W (with PWR set 
to 100W) on 10M and 6M into my Bird TermaLine load and measured with LP-100 
and Alpha 9510 WM.  No big deal but I just wanted to know if this is a 
normal unit-by-unit variation?  This may, or may not be correlated with 
Joe's comment concerning WM slope.

Paul, W9AC

----- Original Message ----- 
From: "wayne burdick" <n6kr at elecraft.com>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Tuesday, September 23, 2008 4:41 PM
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
>
>
> ---
>
> http://www.elecraft.com
>
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