{"id": "card_n_ba6d9264fa3c", "kind": "note", "title": "AM broadcast (medium wave) — where the dial begins", "body": "530–1700 kHz; sealed wavelengths 565 m down to 176 m: https://narrowhighway.com/s/d6211f4efb2518c6de145decf57f27b131a01c24ce7841853f395b7bc986c323 . The waves are so long\nthat the TOWER is the antenna — a quarter-wave at the low end is ~140 m of steel. Channels\nsit 10 kHz apart in the Americas (9 kHz most elsewhere — a regulatory split, not physics).\nThe band's famous trick is empirical: by day the ionosphere's D-layer absorbs skywave, so AM\nis groundwave and local; at night the D-layer vanishes and signals bounce off the E/F layers\nfor hundreds of miles. Amplitude modulation itself is the simplest possible encoding — the\ndiode detector of a crystal radio is enough to hear it.", "source": {"label": "Concordance assay — 2026-07-09", "url": "https://narrowhighway.com/s/d6211f4efb2518c6de145decf57f27b131a01c24ce7841853f395b7bc986c323", "ref": "spectrum_walk", "authority_tier": "engine_derived"}, "shelf": "science", "box": "radio_spectrum", "bands": ["am broadcast", "medium wave", "530 khz", "1700 khz", "skywave", "groundwave", "tower antenna", "radio"], "connections": [], "author": "engine", "created_at": "2026-07-10T01:06:08.948754+00:00", "updated_at": "2026-07-10T01:06:08.948754+00:00", "visibility": "public", "lifecycle_stage": "public", "volatility": "permanent", "surface": "secular", "metrics": {"paperclips_count": 0, "helpful_count": 0, "not_helpful_count": 0, "cite_count": 0, "walks_through_count": 0, "flagged_count": 0}, "source_hash": "6a6ea7e3498f4c54907f4944d271a4a77d03df3132b08aab9ab887bca9e61a5c"}