Hiya jwed, and welcome to the forum
You called the tuner an FT757AT, but I guess you meant FC-757AT (the "C" means coupler).
I've been having a look at the manual for that tuner, and to be honest it's not really cut out to match long wire antennas where the impedance may be quite high or low.
The manual states an impedance matching range from 10~250 Ohms from 80m through 10m, and a range of 25~100 Ohms for 160m (1.8-2MHz).
Like many of the coaxial (unbalanced) tuners, they tend to be more like antenna 'trimmers' rather than 'tuners'.
So the tuner can handle 5:1 SWRs above 80m, and only 2:1 SWRs on Top Band.
If you want to use long wire antennas you could always have multiple quarter wavelength inverted-L antennas, so that at least the SWR/impedance may fall within the matching range of the tuner. You would also need either a good RF earth, or maybe a few counterpoise wires.
Another option might be to have a single wire antenna, with traps fitted at various points for different bands, but it can be a lot of effort for very little improvement.
A useful 'dodge' that you can do with an auto ATU is to make or buy an Un-Un (unbalanced to unbalanced) transformer, with a ratio of between 4:1 up to maybe 9:1.
You run coax out from the ATU to the feed-point of the antenna wire, inserting the Un-Un so that the low impedance side goes to the coax/ATU, and the high impedance side connects to the antenna wire.
The idea is that the Un-Un should then transform down the relatively high impedance of the wire to a range better suited to the ATU.
It might take a little playing around with the wire length/Un-Un ratio to get the system to work on all bands, but when set up correctly you can make some good contacts with the setup.
Hope the above has given you a few ideas to try, and if you need any more help then by all means do post again and ask away!
73 for now, Mark.
