You setup the circuit with a 50Ohm source and then replace it with a capacitor. This de-tunes the circuit. So what can we do?
You could put a short piece of wire on the generator and radiate a signal. Align the set using the antenna it will be using in service. If you are the end user and have the antenna to hook up.
The manufacturer had to develop a way to align the set that would work with their customers antenna. This is what they developed.
The dummy antenna I posted earlier was the industry standard.
IEC standard Dummy Antenna
If you don't want to build the dummy you could use a small capacitor (100pfd - 200pfd) to couple the signal.
If your set has an antenna trimmer you are in luck. You set the trimmer capacitor to a high value while aligning the receiver. Then when you connect the antenna you turn the trimmer capacitor down to allow for the antenna capacitance.
If you align a set with a loop antenna you can couple the generator to the loop.
*EDIT: Next post I measure Zin and apply a signal with lower and higher Z to see the difference.