Operation 1 involves a wired connection from the signal generator to the converter grid via a 0.5µF capacitor. The other operations involve injecting the signal via “one turn (of a wire loop connected to the terminals of the signal generator) loosely coupled to (close to but not tight up against) the waverod (the antenna loop).”
The reason for this is that the first operation aligns the IF, and that needs a signal injected directly into the converter stage. The other operations just take a signal from the antenna.