|Frequency||Capacitance Required||Ham Band||Efficiency|
|21 Mhz||24 pF||15M||89% - 0.5dB below 100%|
|18 Mhz||33 pF||17M||83% - 0.8dB below 100%|
|14 Mhz||55 pF||20M||66% - 1.8dB below 100%|
In theory it would be possible to operate the loop down at 40M with a large enough capacitance but with greatly reduced efficiency ... perhaps a few S units down (8.3 dB below 100%) ... you could push 50W and still fair ok with PSK31 and Olivia in a pinch.