[Elecraft] Homebrew Balanced Autotuner Update

[Don]

Well,  I have had two requests for updates in one week.  Guess I better say 
something.

Early last summer I last posted on this subject asking for any ideas for 
algorithms for autotuning.  I received many replies, all very helpful. 
Since then I  have written the necessary code for autotuning and have been 
using the tuner every day as my standard station tuner.  My K2, my old 
Valiant/SX28A, and homebrew gear all feed through it.

I have found it necessary to be able to place the tuning capacitor at the 
input of the tuner (immediately after the balun) in some cases where I am 
matching a low feedline impedance.  Note that the balun I am using at the 
input to the tuner is a 1:4 balun and so the tuner is matching the feedline 
to a nominal 200 ohm source impedance.  The capacitor switching is done with 
a conventional two pole double throw RS relay and the optimum position of 
this relay for each frequency is stored in permanent memory along with L-C 
parameters and is switched automatically whenever changing operating 
frequency.

I also added a second antenna output.  This is an unbalanced output and it 
is tuned also and in my station it feeds coax leading to an R7 vertical. 
Switching between the two antennas is done via a pushbutton on the front 
panel and the LCD displays which antenna is connected.  This makes it 
convenient  to compare antennas with a touch of one switch .. and the 
appropriate matching L-C is switched automatically depending on the antenna 
chosen.

The only hardware problem I have had is the failure of one of my reed 
relays.  This occurred early just after putting the tuner into service.  The 
relay was one of those connected across an inductor and it was not 'making' 
the circuit when closed.  I am hoping it was a case of infant mortality and 
not the start of a trend.  I have had about 6 months of trouble free service 
since then, usually at the 100 watt level.  I have not attempted higher 
power yet.

I still plan to repackage the tuner into a K2 case.  That will be after the 
holidays.

I am taking my time evaluating the tuner before starting to drill holes etc 
in a nice new Elecraft K2 case.  I want to be sure I really know where I 
want every thing to be and how I want it to work because any modifications 
later will be difficult and could make a mess of things cosmetically.

Don K7FJ