[Elecraft] Auto Tuner Wish List

[Don]

Funny you should ask.  That is almost exactly what I want except I want mine 
to handle at least 500 watts (with *my* antenna anyway) and fit in a K2 
case.

I am designing and building my own.  So far I have a fairly neat breadboard 
operating and when I am ready all of the assemblies of the breadboard will 
fit right into the K2 case.  I am about to order the components for the 
controller and should have that built up and installed in two or three 
weeks.  The controller will be a Basic Stamp BS-2sx PIC, some octal latches, 
an A/D converter and miscellaneous frequency measuring components, 
optoisolators, relay drivers, etc.  The breadboard is for verifying that the 
capacitors, inductors, and relays can handle the stress.  For testing only 
it is controlled by a diode matrix switched by a single pole rotary switch.

My design uses Form A reed switches (the *big* ones) with about 500 turns of 
#38 magnet wire wrapped on them to form the relays I need.  There are 32 of 
them because each of the capacitors are switched in by a pair of relays, one 
at each end of each capacitor to maintain balance by decoupling *both* ends 
of each capacitor which is not in use.  The little latching relays as used 
by Elecraft would be a whole lot quicker and easier but they would not 
handle the voltages I expect at higher power levels.

My design has a homemade balun at the input, two strings of inductors, and a 
single set of capacitors to form a 'balanced L-network'   ... at least that 
is what I call it.  There are 8 capacitors  with the smallest 5 pF stepping 
up binarily (X2 at each step) so that the PIC can switch in any value from 0 
to 1275 pF in 5 pF increments.  Each bank of inductors works in the same way 
with 0.25 microHenry as the smallest increment.

I have a forward and reverse current monitor at the input identical to the 
one in the K2 100W amp but I have not decided if I will go to the trouble of 
putting in a LCD display for SWR, power, band/frequency, etc.  None of that 
is really needed but it would be kind of nice to duplicate the general 
appearance of the K2 with an LCD display.

If anyone is interested in following my progress (or lack thereof) let me 
know and I will provide occassional updates.

Don K7FJ



> Here is what I would like in an auto tuner.
>
> 1. Balanced Output for ladder line - two sets of inductors and one set of
> capacitors (like the Rich Measures roller L design). The inductors can 
> step
> along in parallel.  No control software changes are needed - just another
> set of inductors and relays. The capacitors can switch between the input 
> and
> output depending on the load impedance.
>
> 2. A current balun on the input side of the tuner driving the 2 sections 
> of
> inductors.
>
> 3. 160m to 10m operation.
>
> 4. Matching range somewhat better than the Johnson Matchbox.
>
> 5. A rating for 150W max. power output.
>
> 6. A switch for bypassing the tuner and connecting the ladder line 
> directly
> to the output of the balun.
>
> 7. A peak-reading, illuminated power-output meter.
>
> 8. A 4-position input (rig) selection switch.
>