{"id": "card_n_f9e74aa145cc", "kind": "note", "title": "Varactor — tuning by voltage", "body": "A reverse-biased junction is a capacitor whose plates move with voltage — so voltage\ntunes frequency. The law that seals is exact: since f ∝ 1/√C, halving the capacitance raises\nthe frequency by exactly √2: https://narrowhighway.com/s/1ee0d3ed486453eee0967146a531984888709198b39fb16a7b2c2a5f58ef1b73 — and the tempting error 'halving C halves f' seals\nBROKEN with residual √2 − 1/2: https://narrowhighway.com/s/9ad4a43e7d3c0dd5cea7d1e8756669e79996fc98b70bf02bf35bc143d42108ac . Every phase-locked loop and electronically tuned\nradio rides this. The C(V) profile of a real varactor is an empirical junction property.", "source": {"label": "Concordance assay — 2026-07-09", "url": "https://narrowhighway.com/s/1ee0d3ed486453eee0967146a531984888709198b39fb16a7b2c2a5f58ef1b73", "ref": "electronics_dig", "authority_tier": "engine_derived"}, "shelf": "science", "box": "electronics", "bands": ["varactor", "varicap", "voltage tuning", "electronics", "pll", "junction"], "connections": [], "author": "engine", "created_at": "2026-07-10T00:59:49.508624+00:00", "updated_at": "2026-07-10T00:59:49.508624+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": "99915ce041b4eb2329f84472a4d1bf2b8fe47526caabbc755874f51bb3cd7aa4"}