Any homebrew auto-tuners?

Q.Are there any construction articles around anywhere that describe an auto-tuner similar to the LDG and SGC offerings? I need an auto-tuner that I can control from a laptop, and set frequencies as needed (mostly for ALE). I can do the digital design and the software in my sleep, for an embedded microprocessor that can control all of that, but the heavy-lifting part of the antenna tuner (all the toroids and caps and relays) is a bit beyond my capabilities.

A.There was a two-part (I think) article in QST a couple of years ago which showed a high-power external ATU with onboard microprocessor control. Eliminating the "try lots of combinations to achieve the lowest SWR" part of the system will greatly simplify the RF part of the implementation... you won't need to implement the voltage and current detectors, phase comparators, etc. needed to permit the digital logic to measure SWR, etc. The on-board digital logic might be something as simple as a micro which can [1] run a set of three stepper or gearhead motors to rotate the cap and inductor shafts, and [2] read out DC voltages from a set of potentiometers connected to the shafts. A simple serial-port or USB protocol would then allow the PC to determine the current settings of the reactances, and control the motors to adjust them as needed for a new frequency. A second serial or USB port would be used to communicate with whatever your rig is, to either read out the frequencies being tuned, or to switch the rig to a different frequency. A similar system could be done with switched banks of inductors and caps, in the usual power-of-two size hierarchy. In this case, the micro would be just ordered to turn on or off the various relays used to switch toroids and caps in and out of the series and shunt circuits.

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