[Elecraft] K3 pwr out on digimodes

[Julian, G4ILO]

Don Wilhelm-4 wrote:
> 
> The K3 suggested ALC level for digital modes is *4* bars.  The 6 bar 
> indication is for SSB (actually listed as 5-7 bars).
> According to the K3 FAQ page - when the indication is at 5 bars, the DSP 
> ALC is just being "tickled".  For data modes, ALC action is not 
> desirable, thus the 4 bar recommendation.
> 
> Up to (but not including) the 5th bar on the ALC meter, the meter is 
> indicating something similar to VU units rather than ALC action - the 
> 5th bar is the onset of ALC.
> 
> 

I did my test for output over a range of frequencies with 4-5 bars of "ALC"
and as I stated, the power varied by about 2dB. If ALC is being applied at
the DSP that is just plain wrong in my opinion, as it cannot compensate for
the variations in gain at different frequencies due to the shape of the
filter.

When ALC is applied at the output, as in SSB mode, the effect is a flat
response. As long as only a little ALC is used there is no adverse effect on
transmitted IMD when using PSK31.

I think the dangers of using ALC when running PSK31 have been wildly
overstated in some quarters. I have always operated PSK31 using just enough
audio drive to give a bar or two of ALC and now having the KK7UQ meter I
have been able to measure the effect of this when using an FT-817, K2 and
K3. On the FT-817 some worsening of the IMD is noticeable but the signal is
still clean, typically -27 or -28dB. On the K2 one bar of ALC makes no
difference at all. Incidentally the K2 has the cleanest PSK31 signal of all,
typically -33 or -34dB at 5W output. The K3 at 5W on 80m measured -28 or
-29dB whether using DATA A mode (with no 'real' ALC being applied) or SSB
mode with one or two bars of real ALC.

-----
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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