The part in the right upper corner is the RF probe and it's very useful when testing RF oscillators and RF power amplifiers, to see if they're oscillating at all. It's also useful when fine tuning an RF amplifier, to see at which point it transfers most power (e.g. to fine tune any resonance point there is). The red LED will enable at the best tuning point and only at RF power levels of ≥3W.
