The following pictures show the voltage waveforms at the MOSFET drain terminal (test point T4 on the circuit board) for various settings of the tuning trimmer capacitor. Freq = 1550kHz, Antenna Capacitance=30pF, Rrad+Rgndloss=33ohms. "PWR IN ADJUST" control unchanged. It was set for 100mW for the 3rd picture below, but was left unchanged from that setting for all the others.
I am hoping that this will help convince everyone that an oscilloscope is NOT required for tuning. Instead, simply adjust the coil tap jumper and trimmer for maximum input current, then adjust the trimmer 1 full turn clockwise, and then adjust the "PWR IN ADJUST" control for 100mW input power. This simple trimmer "trick" works very well over the 1350kHz - 1700kHz frequency range of the toroid coil and an antenna ground loss resistance range of 10ohms - 75ohms.
Notice particularly that the "Power In" is maximum when tuned for max power in (first picture), but the efficiency is only 78%. When tuned to maximum efficiency, the Power In drops, but that drop is compensated for by the final tuning step where you set the power in back to 100mW. The radiated signal power is maximum at the highest efficiency tuning point and 100mW input power. All other tunings with legal Power In will result in lower radiated signal power.
If you want to use an oscilloscope, connect the probe to test point T4 (MOSFET drain) and connect the scope probe ground to test point T1 (ground). Maintain the scope trigger for a stable display. Adjust the coil tap jumper and trimmer to get maximum input power on your voltmeter. The scope should show the first waveform below. Then adjust the trimmer to approximate the third picture below. Then adjust the "PWR INPUT ADJ" control for 100mW.
Tuning trimmer set for maximum input current meter display
Power In = 0.140W
MOSFET drain efficiency = 78%
Tuning trimmer set .42 turn clockwise (+.3pF)
Power In = 0.131W
MOSFET drain efficiency = 93%
Tuning trimmer set 1 turn clockwise (+.7pF)
Power In = 0.100W
MOSFET drain efficiency = 99%
Tuning trimmer set 1.4 turns clockwise (+1.0pF)
Power In = 0.058W
MOSFET drain efficiency = 99%
Tuning trimmer set 2 turns clockwise (+1.4pF)
Power In = 0.037W
MOSFET drain efficiency = 94%
Tuning trimmer set 3 turns clockwise (+2.1pF)
Power In = 0.028W
MOSFET drain efficiency = 60%