[Elecraft] Homebrew Autotuner

[Don]

A few months ago I maintained a brief correspondence with some on this list 
with an interest in a homebrew balanced autotuner.  The project is nearing 
the point where I will be installing it into a K2 case.  At the moment, 
though, I am having trouble coming up with a software algorithm that finds 
minimum swr and this message is a request for suggestions.

I have found that it is not as easy as I had imagined.  I have been using 
several methods to automatically find minimum swr and some work pretty well 
most of the time but none work well *all* of the time.  The problem is that 
on some bands minimum swr occurs over a very narrow range of C and L.  With 
either C or L are set only a little off of these optimum values any change 
in C or L will have  *no* effect on measured swr.

I have used complex algorithms that vary step size, vary C and L values 
intelligently with either positive or negative changes in value.  I have 
used simple algorithms that stupidly go through an entire range of 
possibilities of all values of L for every C and so forth (ugh!) ... and 
have to believe there is someone out there in Elecraft-land a lot more 
clever than I who can suggest ways to intelligently find best combinations 
of L and C  quickly using measured swr as the criteria.

It really does not matter a great deal if I never perfect the autotuning 
feature of the tuner.  It is easy to manually tune the tuner,  store L and C 
for every band segment in nonvolatile memory, and then let the tuner 
automatically switch to the proper values when it senses the frequency at 
the input.  But I can't call it an autotuner if it doesn't tune well 
automatically can I?  Perfectionist that I am I would like to make it 
autotune like it is supposed to.

Any ideas?

Don  K7FJ


  http://www.qsl.net/k7fj/