[Elecraft] K3 pwr out on digimodes

[Julian, G4ILO]

Leigh L. Klotz Jr WA5ZNU wrote:
> 
> Most digimode programs include a tune button which outputs a tone at the
> selected output; psk's idle is a simple two-tone.  One option (and I
> expressed this a year or so ago to the Elecraft folks) would be to offer
> an IMD calibration at the IF level for a known two-tone response, to
> determine whether at least that stage is being overdriven.  The DSP should
> have a fairly good idea at that point.  If the two-tone signal used is a
> PSK idle tone at the selected AF on the waterfall display, a rig control
> command to read the IMD calculated would be just peachy.  Digimode
> programs could then have a dedicated button to send an idle tone, read the
> IMD, and adjust the power.  Regular communications could then commence.
> 
> A further advantage of this approach is that the actual power out could be
> measured during this calibration period from either the built-in wattmeter
> or the rig control command, and reported in real time, and thus the knob
> could (or again, rig control) could be used to achieve the output power
> desired by the user.
> 
> Elecraft's response was that perhaps the IMD calculation could be done on
> the computer side; I'm not clear whether the new monitor out function
> makes that possible or not, but if it does, that would be an approach that
> could be made to work today, modulo the limitation that the IMD calculated
> from the sound card will be a little worse due to the additional ADC of
> the sound card, whereas a digital report from the K3 IF would be accurate.
>  (And not to mention that an overdriven line input would result in a
> drastically wrong IMD, but that's likely to have been already taken care
> of by the digimode RX setup.)
> 
> In summary, I believe it's possible to provide closed loop control for
> both power and drive/IMD readings for modes such as PSK, but not during a
> QSO where the signal characteristics vary; instead provide enough CAT
> commands and signal quality measurements from the K3 RF OUT and IF OUT
> stages so that and digmode authors are willing to provide a "TX CAL" tune
> button.  (Doing in the k3 utility wouldn't be helpful because the precise
> audio settings used by the digimode program for TX are important.)
> 
> I'm willing to step up and try this for fldigi.
> 
> Leigh/WA5ZNU
> 

I'm not sure that what you are suggesting is entirely possible. Surely IMD
depends on a lot of other variables that happen after the IF, such as output
power level, supply voltage level and SWR? I don't see how the K3 could
actively monitor IMD without building functionality akin to the KK7UQ meter
into it. In any case, there are other modes besides PSK31 to which the IMD
issue does not apply, but the problem of varying power levels across the
passband still do.

I think this whole issue has come about because the K3 is trying to be too
clever and prevent people from transmitting a PSK31 signal with poor IMD. If
someone is dumb enough to put too much audio into the input and use way too
much ALC then that is their lookout. We are supposed to be trained operators
who understand what we are doing. If we make mistakes, we learn. The K3
doesn't try to stop people winding the mic gain up too much when using SSB.
Why should it act any differently just because the DATA mode is selected?

DATA mode is just SSB. Its only purpose is to facilitate selection of a
different input source, disabling compression, and disabling passband
equalization. Nobody expects it to behave in any other respect differently
from how it handles SSB.

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