🔍 Key Concepts
• BFO (Beat Frequency Oscillator) – what types of signals actually need it to make audio intelligible
• Different emission designators: A1A, A3E, H3E, J3E, J2B, F1B (CW, AM, SSB, FSK/DSC, etc.)
• Which modes are compatible with a plain AM receiver (no BFO) and which require product detection
💭 Think About
• For each emission in the options, decide: is it continuous wave (CW), normal AM voice, single sideband, or frequency‑shift keyed data?
• Ask yourself: if I had a basic AM receiver with the BFO turned off, which of these signals would still sound intelligible as voice or tones?
• Which modes absolutely rely on the BFO to recreate the missing carrier or to turn on‑off keying into an audible tone?
✅ Before You Answer
• Identify which designators correspond to SSB with suppressed carrier (J3E) and SSB with reduced carrier (H3E), and whether those need BFO for reception.
• Determine which emissions are on‑off keyed CW or data (e.g., A1A, F1B, J2B) and whether an AM detector alone can turn them into useful audio.
• Eliminate any options that contain only modes that need the BFO to be heard or decoded properly.