I suddenly remember watching the demonstration of the use of a slide screw tuner to correct the impedance mismatch between the spectrum analyzer and an amplifier, bring the point to the centre of a Smith chart(at 35 minutes):
https://youtu.be/ToVJTKCyIU8
These are very neat looking devices that can work as low as 600MHz:
https://focus-microwaves.com/wp-cont...rew-Tuners.pdf
https://manualzz.com/doc/21325695/sl...rs-description