[Elecraft] K3 Compression compared to CESSB

[Bob McGraw K4TAX]

I have studied and measured both the Compression algorithm and, as a 
separate project, the ALC operation using my K3S.  It is clear the ALC 
system is very different as implemented in the K3S from other radios in 
as much as there is some gain ranging which occurs below the 5th bar of 
ALC indication.  After and above the 5th bar the system goes into a gain 
reduction scheme, somewhat typical of other ALC systems.  One key to ALC 
systems which make them very different is the attack time the release 
time and the compression/limiting ratio, meaning input signal change vs. 
output signal change.  All in all, the K3S system is very clever and 
much like audio processing as used in commercial broadcast 
applications.  Perhaps this accounts for the excellent results.

This is clear for those that work digital modes and are instructed to 
adjust the input level to the point the 5th bar is flickering when using 
the K3S.  Clearly, until one understands this, most revert to 
instructions found with digital programs, digital interfaces and other 
radios which clearly say "adjust to the point below ALC action".  In the 
case of the K3s, there is really no ALC action below the 5th bar.  In 
fact the value as show on the ALC scale below the 5th bar is more of a 
VU type indication with some degree of level expansion.

As to CESSB, the articles in QEX and QST February are very interesting 
and enlightening.   It is interesting note that the CESSB methodology 
increases the average power by a factor of some 2.5.  Of course the 
major advantage is not only increased average power output but greatly 
reduced distortion as a result of the method employed.

It will be very interesting to see how all this plays out in regard to 
implementation in future radio designs.

73
Bob, K4TAX



On 1/22/2016 9:47 AM, Robert Sands wrote:
> Given the recent article in QST explaining CESSB I looked for some detail
> about the compression algorithm of the K3 but found nothing explaining how
> it works.It is the most effective processing I have ever used and appears
> to double the transmit power. So perhaps it is a version of CESSB or
> efficient enough to be left alone as is. Perhaps I missed some discussion
> on this.Is there a published explanation of the compression algorithm? (not
> in Fred's book, I looked and checked with him)
> Bob
> K7VO
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