I have an auto tuner whose specs for the output a
"10 to 250 ohms"

Does that have any useful information other than perhaps the R part of R+j.

That's not particularly comprehensive information, since it doesn't
say whether it's R, or |Z| that it's describing, and doesn't say
what frequency range this spec might apply to. It's likely that any
auto-tuner (or any manual one!) will have different matching ranges on
different bands.

This spec *might* mean "This tuner will successfully match most loads
within a 5:1 SWR range, on most of its bands, most of the time."

Or, it might mean much less than that.

You could ask the manufacturer for a full specification on the actual
impedances that can be matched on various bands (e.g. a set of Smith
charts). They may or may not be able to provide them.

If you know what the switchable reactances inside the tuner are, and
what the switching topology is (most likely a bidirectional "L" but it
might not be) then you could calculate and plot the outer envelope of
the matching range for any given frequency. The math isn't too
terrible.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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