Option A: Incorrect. Local oscillator output isn't the RF envelope - that's an internal signal, not the transmitted signal. You need the actual RF output. Option B: Incorrect. External RF oscillator isn't needed - you want to check your transmitter's output, not an external signal. External oscillator doesn't show your transmitter's envelope. Option C: Incorrect. Balanced mixer output isn't the RF envelope - that's an internal signal before final amplification. You need the final RF output.