[Elecraft] Fwd: Re: K3-P3 SSB spectrum

[Joe Subich, W4TV]

> The internal power control loop then measures the power level of the
> RF being made and adjusts it to meet the requested level.

There is *no "power control loop"* in the K3 - that is the difference
between the K3/K3S and traditional (YaeComWoood) transceivers.  When
you (or the factory) performs the TX Gain calibration, the rig learns
how much (digital) gain is required in the DSP stage to drive the LPA
(5W setting) and the KPA3 (50W setting) to reach the desired power
level.

Since the transmit chain of the K3/K3S is linear (unlike YaeComWood),
when you request 100W instead of 50W the controller knows to increase
the voltage output of the DSP by a factor of 4 (3dB) while if you
request 20W the output of the DSP will be reduced by 4 dB (20/50 W =
-3.98 dB).

Because there is no "power control loop" the K3/K3S does not suffer
from overshoot, ALC induced distortions, IF clipping, PA over-drive,
etc. that plague traditional solid state transceivers.

73,

    ... Joe, W4TV


On 2015-06-08 5:16 PM, Fred Jensen wrote:
> I think understand this but then of course I thought I understood
> Economics 101 in college which turned out to be seriously untrue ...
>
> Turning the MIC GAIN way up on say an HT-37 increased the drive to the
> PA and eventually saturated it, creating havoc on the band.
>
> The K3 does not control power with the MIC GAIN.  The PWR control sets a
> "requested" power output.  The internal power control loop then measures
> the power level of the RF being made and adjusts it to meet the
> requested level.
>
> On SSB [and AFSK/DATA A] the MIC GAIN needs to be high enough so that
> the power control loop can meet its target power,  That's the first 4
> bars of the ALC meter.  Anything higher than that just lowers the system
> gain til the target power is met.  Or something like that [while waving
> arms]...
>
> I would imagine that turning the MIC GAIN way up would get a lot of
> extraneous room noise onto your signal.  I don't get on SSB all that
> often, but mine is set for 4 bars with the 5th just flickering on peaks,
> and 10 dB compression on peaks.  Other people seem to like it when I
> talk to them.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
> - www.cqp.org
>
> PS: There was never any doubt that I did *not* understand O'chem.
>
>
> On 6/8/2015 10:56 AM, Richard Fjeld wrote:
>> Just a comment somewhat related to this thread.  Not long ago, a ham
>> with an SDR set-up was comparing signals in a round-table for proper
>> bandwidth.
>>
>> He said my signal was very clean and asked me to crank up my Mic gain
>> to the max which I reluctantly did for a short transmission. He said
>> it stayed clean with no splatter.  Can that be? I thought any radio
>> would splatter if over-driven.
>>
>> For me, seeing is believing.    Dick, n0ce
>>
>>> Date: Sun, 7 Jun 2015 16:58:26 -0400 From: lists at subich.com To:
>>> elecraft at mailman.qth.net Subject: Re: [Elecraft] K3-P3 SSB
>>> spectrum
>>>
>>>
>>> The TX Monitor is a time domain display - not a frequency domain
>>> display.  If you want to see the frequency domain display of your
>>> own signal, temporarily disconnect the RS-232 cable between the two
>>> (or connect another SDR to a directional coupler in the antenna
>>> line).
>>>
>>> 73,
>>>
>>> ... Joe, W4TV
>
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