fix(math): re-calibrate feedpoint-R model against nec2c (corrects fnec anchors)#135
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…c anchors) Cross-validating the T3 dipole feedpoint-R model against nec2c (NEC-2) revealed the fnec-rust anchors it was built on are physically wrong: they make R FALL with height (73→52.8→45.6 Ω at 7/10/12 m) and carry ~−95 Ω reactance for a resonant dipole. nec2c — validated here against the textbook free-space half-wave R (72.1 Ω) — shows R correctly RISES with height toward a peak near ~0.3 λ. nec_calibrated_dipole_r is re-derived from a full nec2c ground matrix (poor/average/good × 7/10/12 m), still interpolated on height-in-wavelengths, so the feedpoint R and SWR estimates for dipole-family antennas are now physical: 40 m good ground reads 57.6 / 78.9 / 86.5 Ω at 7 / 10 / 12 m (was 73 / 52.8 / 45.6). - corpus/nec2c-reference.json: committed ground matrix + free-space value. - corpus_nec2c_dipole_ground_feedpoint_r_matrix: CI-gated 9-cell validation. - unit test + docs/math.md §4 range + requirements.md GAP-011 updated. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Backlog T9 — ground-plane NEC validation surfaced a real correctness bug in the T3 feedpoint-R model.
Finding
Cross-validating
nec_calibrated_dipole_ragainst nec2c (NEC-2) showed its fnec-rust anchors are physically wrong:nec2c is trustworthy here — it reproduces the textbook free-space half-wave R (72.1 Ω) exactly.
Fix
Re-derived
nec_calibrated_dipole_rfrom a full nec2c ground matrix (poor/average/good × 7/10/12 m), still interpolated on height-in-wavelengths. Feedpoint R / SWR estimates for dipole-family antennas are now physical.Behaviour change: e.g. 40 m good ground now reads 57.6 / 78.9 / 86.5 Ω at 7 / 10 / 12 m (was 73 / 52.8 / 45.6).
corpus/nec2c-reference.json: committed ground matrix + free-space value (regen viascripts/nec-reference.sh).corpus_nec2c_dipole_ground_feedpoint_r_matrix: CI-gated 9-cell validation, guarding against regression to the old anchors.docs/math.md §4, andrequirements.mdGAP-011 updated.cargo testall pass, clippy + fmt clean. Reactance is still not modelled.🤖 Generated with Claude Code
https://claude.ai/code/session_01Jf8uBU8AYxkrG8fa8yo6tC