🔍 Key Concepts
• Emission designations: what each character in "J2B" means according to ITU (type of modulation, type of signal, type of information)
• Difference between single-sideband (SSB) signals and full-carrier AM signals
• How automatic telegraphy (for machines, not for the ear) is usually sent: on/off keying of a tone vs shifting between two tones
💭 Think About
• First, decode "J2B": what does J say about the carrier and sidebands, what does 2 say about the modulating signal (single tone vs two tones vs no tone), and what does B say about the type of information?
• Look at each answer choice and decide: which ones describe a full carrier, and which ones describe a suppressed carrier, single sideband? Eliminate any that don’t match "J".
• Between the remaining choices, ask: for automatic telegraph reception, is it more typical to switch one tone on and off, or to alternate between two different tones (mark and space)?
✅ Before You Answer
• Verify which letter indicates single-sideband, suppressed carrier in the emission code (this must match the description of the carrier and sidebands).
• Verify what the digit 2 means: "single channel digital with a modulating subcarrier" – does that suggest on/off of one tone or shifting between two tones?
• Verify that B stands for "telegraphy for automatic reception" (not for aural reception), and match that with the kind of tone pattern a machine would best detect.