LDG does not specify either max C or max L of their antenna tuners in the “pro” series. They specify a vague “it can tune 1000 ohms”. This basically means nothing as no frequency is given and it is not given if they mean R or X or Z by “1000 ohms”. There is also no service manual or schematic available. Very disappointing from a serious (?) supplier.
Well, since LDG doent specify anything, I have measured it.
The LDG AT-100PROII is a series L, shunt C configuration.
Min L is 3uH, max L is 11,8uH
Min C is 85pF, max C is 250 pF
This is measured at 2MHz.
This shows that the capability of tuning an 2x20m doublet via “10-12m” of 590 ohm ladder line on 80m seems to be limited, and that tuning on 160m is very difficult.This is mainly due to limited Lmax. Also the limited Lmax gives limitations on other bands as well. Having the proper length of transmission line is important to overcome this limitations. You MAY also use a 4:1 or 9:1 balun. However it is important that the balun does have a very low loss. (Otherwise you you end up with a good SWR but poor efficiency).