I am currently experimenting with an improved design for my Superlight SOTA Vertical. The main problem with the current design, which the QRPguys base version will likely exhibit in the very same way, is that the SWR varies greatly with the type of ground and the exact deployment. In most cases, it is possible to get the SWR to an acceptable level by tuning the radial(s), but this can be a time-consuming process.
My current take (not yet implemented) is to
add a variable capacitor in parallel from either end of the inductor to ground and make that switchable with an on-off-on switch. By that the, simple loading coil turns into an L-match and can thus also provide impedance transformation, and
replace the existing on-off-on switch for the 40-30-20m adjustment of the inductor by a tiny 8-position rotary switch and additional taps at the inductor so that you will always have at least one position with less and more inductance for 40, 30, and 20 m.
As for the inductor, I am inclined to use a small air coil (d = 20 mm, l= 30 mm, Nmax = ca. 40 turns) instead of the toroid, for (a) it will only be marginally bigger, (b) have a better Q (?), and © it will be easier to build a tapped version.
This version will make it unnecessary to carry an extra tuner and still be able to make the antenna usable under imperfect conditions.
Another option I am considering is buying a Miracle Whip antenna unit and replacing the whip by the 5 m radiator and a 5 m (or so) radial. The Miracle Whip design uses a variable autotransformer (i.e. a tapped inductor on a toroid with a variable tap position). The regular miracle whip antennas are often criticized for their poor tx performance, but that is largely due to the tiny radiator of 1.5 - 1.7. With 5 m on a fishing rod, performance should be much better.
Tuning with the autotransformer will be simpler (one dial). Many Chinese Miracle Whips now include a Tayloe SWR indicator, too, like this one:
What might also be interesting for others in the search for the ideal SOTA Vertical is this upcoming product from Wonder Wand. It seems to combine the idea of a tunable counterpoise/radial with a miracle whip matchbox and single dial:
See also here:
73 de Martin, DK3IT