I don't have experience with that particular antenna, but I have extended the tuning range of my other small loops (PreciseRF, RF319) by using longer, shorter or multi-turn LMR-400 loops in place of the ones provided.? Using two different-length loops permits making three combinations by using them individually or connected in series; longer loops can be formed into two (or more) turns.? ?
I added a 3:1 reduction drive to the HF319 which eases tuning and reduces hand effects, the PreciseRF has motorized tuning.
The HF319 loop switches the connections of the tuning capacitor and loop to switch bands; note that connections are made to both inner and outer loop conductors, unlike many designs which only use the shield.? Perhaps other designs could be similarly modified to provide a second range.??
Changing the loop size is simple and can likely be implemented with materials at hand; they are just coaxial jumpers of various lengths.? My nanoVNA makes experiments quick and easy.
73, Don N2VGU ?
Donald S Brant Jr