🔍 Key Concepts

• F1B/J2B emissions are types of narrow-band direct-printing (NBDP) telegraphy used in maritime HF and MF bands • Channel spacing is the separation between adjacent assigned frequencies, typically expressed in Hz or kHz • Think about standard international HF NBDP channel plans and their typical spacing

💭 Think About

• Are F1B/J2B channels spaced more like very-low-frequency audio filters (hundreds of Hz) or like standard radio channels (kHz range)? • Compare the sizes: which of these values would practically allow many distinct NBDP channels across a small HF band segment? • Which spacing value is consistent with other narrow‑band digital/telex maritime services (e.g., 500 Hz, 1 kHz, 3 kHz, etc.)?

✅ Before You Answer

• Make sure you are thinking about radio channel spacing, not audio tone frequency differences • Ask whether 170 Hz or 300 Hz is more typical of frequency shift (FSK shift) between mark and space, rather than channel spacing • Confirm which option matches standard HF narrow‑band data/telex channel spacing used in ITU maritime allocations