Rick (W-A-one-R-K-T) wrote:
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.

If there are any construction articles that I can adapt to my needs that
would be a very big help.

Thanks...


The original LDG tuner was described in a construction article in QST,
including a schematic. The SGC manuals have the schematic in them.

Practically speaking, it's just a bunch of relays. The hard part is
finding suitable relays. The LDG uses a L network with the capacitor
switched either to the input or output and inductors wound on toroid
cores. The SGC uses a pi network, and closewound air core inductors.

The values are in an approximate powers of two sequence (allowing for
standard values and the fact that you only get integer numbers of turns)
Capacitors in the AT11: 5,10,20,39,82,160,320,640 pF
Inductors in the AT11: 0.11, 0.22, 0.39, 0.59, 1.25, 2.5, 5, 10 uH


how much power are you going to run and what's the maximum mismatch?
that determines the size of the wire in the inductors and the
current/voltage ratings of the capacitors.
You also want to decide if you want latching or non-latching relays.
Most modern tuners use latching relays because after tuning, you want
power to be reduced to a minimum. For ALE, this might not be as big a deal.

Most modern tuners also implement some sort of frequency counter, which
is then used for a lookup table to find a previously set configuration.

Another key design aspect is that you probably want to shut down the
microprocessor after tuning, so that you don't have spurious signals
from the microprocessor clock. Either that, or choose a clock frequency
where the harmonics don't fall in *bad* places.

I've gone through the design and build exercise several times. Unless
you're doing it for the experience of designing an autotuner, I suspect
that buying a ready made tuner like the LDG AT200PC, which has a RS232
interface, is probably the cheapest and easiest solution. It has a
published control protocol which is easy to work with (except that you
need to be able to generate a pulse on RTS to wake it up...).


Jim, W6RMK