Can a manual antenna tuner be used with a TS-590SG?
Yes it certainly can. A manual tuner can be used with any rig. You need a small amount of rf from the radio to the tuner and then adjust the tuning. You can do this most easily by reducing the output power to 5 watts and setting it on cw and holding the key down as you tune the antenna. The tuner needs some power to it and then adjustment to tune the antenna. You can do this for each band and mark or record the settings so that you can tune from band to band easily when you know how to set the manual tuner, then just “tweak” it once on that band.
As you know, the TS-590 SG has an internal automatic tuner. However, using an external manual tuner can tune a wider range of swr as well as tune very low frequency antennas on 160 m or 80 m much better than the internal tuner.
If you disable the internal tuner (menu 51/52 Off), you can use the “tune” button on the radio to trigger the 10W tuning signal to use your manual tuner.