As others have noted, it's certainly possible to do with the only moving
parts being relays -- there are several commercial tuners on the market
in this category.

But it'll be awfully tough to replace the relays, if your intention is
to transmit. Relay contacts have very high impedance (low capacitance)
when off, and very low resistance when on. They'll handle very large
voltages and currents. And the impedance, both on and off, doesn't
change with applied signal level. There isn't any other component that
has all these characteristics, and some or all are required in a wide
range tuner. You might, by very careful analysis of the circuitry under
various load conditions, come up with some sort of switch (e.g., PIN
diode, VMOS FET, etc.) which can handle the voltages and currents at
each switch point, while having acceptable on resistance, off
capacitance, and linearity (non-variation with signal level). But it
won't be a simple task. And you'll probably still have to sacrifice some
efficiency and tuning range.

In a receive-only tuner, you still have the problem of getting adequate
on and off impedances, but you are relieved of the voltage and current
requirements.

Relays are just simply very hard to beat for some applications -- and
this is one of them.

Of course, you can try varying the L and/or C by a number of methods,
such as others suggested -- using saturable reactors for L and varicaps
for C. Again, though, you run into voltage and current limitations. And
these devices tend to be nonlinear -- that is, the L or C depends also
on instantaneous signal level. So when they encounter a large signal,
they create distortion which produces harmonics. This would be a fine
approach for a receive-only tuner, but not a good one if you want to use
it for transmitting.

So, that's how you do it. Good luck!

Roy Lewallen, W7EL

Andrey wrote:
How do I design an automatic antenna tuner with no moving parts?

This is a good question.

How to do it - without relays, motor driven capacitors and inductor cotacts?