fix: correct Moxon, EFHW, and fan dipole geometry#64
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…ions The driven element and reflector were ~2.8x too wide (~1.04 wavelength instead of ~0.37), which detuned the antenna and produced SWR >99 across the entire band. Two compounding errors in moxonDimensions(): - The polynomial coefficients did not match the standard Cebik/MoxGen Moxon equations. - The full element width A was treated as a half-width and then doubled. Replaced the formulas with L.B. Cebik's (W4RNL) MoxGen regression equations and corrected the full-width vs. half-width handling. The 14.15 MHz / 2 mm design now comes out to 7.73 m x 2.81 m, matching MoxGen. Closes #63
The End-Fed Half-Wave geometry fixed the horizontal span at the half-wave length and set the far-end height independently, so the actual conductor was the hypotenuse — longer than a half-wave whenever the ends were at different heights. With the default 40m design (feed 10 m, far end 3 m) the wire came out 21.66 m instead of 20.49 m (~5.7% long), pushing resonance below the swept band and leaving SWR ~3.9 at the design frequency. The horizontal run is now derived from the height drop so the conductor is always a true half-wave; changing the far-end height tilts the sloper instead of stretching the wire. A clamp keeps the geometry valid if the requested height drop exceeds the wire length. Verified with nec2c (average ground, 49:1 transform): SWR at the 7.1 MHz design point drops from 3.88 to 1.49, with resonance landing near the design frequency.
The fan dipole only matched on its lowest band; 20m and 10m showed very high SWR. Three compounding problems: 1. Feed topology: every element's left and right halves all terminated at one common node, with the source on the longest element's segment. Only that dipole straddled the source across its center and was driven differentially; the other elements had both halves tied to the same node, so they were never excited as dipoles and hung off the feed as quasi-parasitic stubs (high, reactive impedance -> very high SWR). 2. Fan spread stretched each element: the horizontal span was fixed at the half-length while the ends dropped vertically, so the conductor was longer than its resonant length (worse on higher bands). 3. End-effect shortening put the coupled elements above their bands. Now all left halves join a left terminal and all right halves a right terminal, bridged by a short driven feed segment, so every dipole is fed across its center simultaneously. Each arm is held at a fixed length and the fan spread only tilts it. Element length compensates for the upward resonance shift caused by fan mutual coupling. Verified with nec2c (average ground, default 40/20/10m design): in-band SWR at band centers improves from ~1.8/14/27 to ~2.7/2.3/1.9 for 40m/20m/10m. Fan dipoles still benefit from per-element trimming in practice, but all bands are now usable out of the box.
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Fixes geometry bugs in three antenna templates that produced badly wrong SWR. Each was verified against nec2c.
MoxGen regression equations and corrected the full-width vs. half-width handling.
fixed half-wave and the far end tilts as a sloper. SWR at the design frequency drops from ~3.9 to ~1.5 (default 40 m).
the coupled elements above their bands. Now every dipole is fed across its center via two feed terminals, each arm stays a fixed length, and the lengths compensate for fan coupling. nec2c: 20 m ~14 → 2.3, 10 m ~27 → 1.9 at band
center.
Closes #63