[Elecraft] K3 - SPE Expert 1K-FA and ALC

[Tom W8JI]

>>However, Gianfranco of SPE (Expert) suggests running the 
>>exciter at full power.  He says there is no splatter and 
>>the proof of the pudding is in the eating.  >>That seems 
>>to be true.  I can't see any splatter on the WaveNode and 
>>several on the air tests report fine audio with no 
>>splatter.

>>I repeat:  There is something here we don't understand.

We went through this ALC stuff just one month or so ago. The 
problem with ALC is the ALC system response delay and the 
propagation delay through the radio, especially narrow 
filters. The leading edge of everything takes a hit until 
the ALC level comes up. The time delay to interact with the 
system is the problem. With a reasonable ALC hang time the 
splatter is not too objectionable on a crowded band, but on 
real quiet bands it can be disruptive to weak signals. It is 
a very broad bandwidth short duration problem.

In my opinion it isn't the major problem we face with SSB 
bandwidth and we may be over focusing a little on it. The 
duration is so short the average power is very low, but it 
is there. It would be very easy to miss on a spectrum 
analyzer, as a matter of fact I would say it is nearly 
impossible to catch. A selective level meter would be a far 
better detector.

The real problem is the K3 has a unique ALC system that is 
in front of the filtering, so leading edge delay isn't an 
issue. Since the K3 has no leading edge transients, and 
since anything after the radio (except a clamp or fast 
attenuator) can not fix the transients, I don't see why 
anyone would want to run external ALC with the K3.

Here is what Wayne said:

<<<<<<<<<<<<<<<<<<<<<<<
K3 external ALC setup is covered on page 27 of the owner's 
manual.
Please read this page before attempting to use external ALC 
with any
amplifier.

Executive summary:

1. DO NOT turn the K3's power all the way up and use 
amplifier ALC to
maintain peak power at the output of your amplifier. This 
WILL NOT work.

2. Instead, adjust the power level at the K3 to provide just 
enough
drive to hit the peak power desired at the amp. You may want 
to set
CONFIG:PWR SET to PER BAND so you don't have to adjust power 
each time
you change bands. (This is also covered on page 27.)

3. External ALC is accommodated as a safety backup in the 
event that
peak power suddenly increases, etc., due to a failure or 
load change.
When properly applied, it will rarely be needed.

Technical details:

The K3 is designed to *not* depend on fast external ALC, 
because that
absolutely, positively causes splatter. We studied lab work 
from
several authors on this topic and decided to take a 
different
approach: our fast ALC is all applied *ahead* of the 1st 
I.F. crystal
filter (it's handled by DSP, at the AF and 2nd I.F. stages). 
We do
apply slow, long-term ALC after the crystal filter, but this 
can't
cause splatter because of the long time constant. External 
ALC, if
used, is factored into this part of the equation.

Yes, the K3 is unique in this regard. It may be slightly 
inconvenient,
but it will result in a cleaner signal.

73,
Wayne
N6KR

>>>>>>>>>>>>>>>>>>


73 Tom