Ember Hollow

📡 Ember Hollow is a working antenna bench for your phone. Pick a design, set it for your band, and the app solves what that antenna actually does — the current on every element, the radiation pattern in three dimensions, the feedpoint impedance, the SWR across the band, and the cut list you build it from.

Nothing is looked up. Every number is computed on the device, from the geometry you gave it. 🔧

WHAT IT SOLVES

• Half-wave dipole, folded dipole, 3/5/7-element Yagi-Uda, quarter-wave ground plane, and small magnetic loop — all generated from your frequency, not stored as fixed dimensions.
• Bands: 10 m, 6 m, 2 m, 70 cm, 433 MHz ISM, 868 MHz LoRa and 2.4 GHz.
• The radiation pattern as a surface you can turn over with a finger, plus E and H plane cuts on shared dB rings with the half-power points marked on the curve.
• Gain, front-to-back ratio, beamwidth and side-lobe level.
• SWR swept across the band — the bare feedpoint and the matched result on one axis, so you can see what the matching network costs you in bandwidth.
• A real Smith chart with the sweep drawn as a locus, and four matching topologies solved with component values you can actually order.
• Feedline loss for RG-58, RG-213, LMR-400 and 450 Ω ladder — including the extra loss the mismatch itself causes.
• A dimensioned build sheet with per-band cut tolerances, exportable to your photo library so it can come to the workshop with you.
• A field log: photograph what you built, record the SWR your meter actually read, and watch the app grade its own prediction over time. 📊

HOW IT WORKS

The engine uses the induced-EMF method — one sinusoidal current per element, self and mutual impedances in closed form, and a direct solve for the element currents. The pattern is then computed from those solved currents, never assumed.

It is checked against textbook reference values, including a half-wave dipole at 73.1 + j42.5 ohms and 2.15 dBi. 📐

When the method stops being valid — an element past 0.9 wavelengths, or conductors too fat for thin-wire theory — the app says so and declines to print a number instead of giving you a confident wrong answer. The Learn section explains the assumptions and limitations.

📴 COMPLETELY OFFLINE

No account, sign-in, sync, analytics, ads or tracking. Your saved designs and measurements stay on your device.

🎙️ FOR

Radio amateurs, LoRa and ISM builders, Wi-Fi link builders, RF students, and anyone curious about where antenna dimensions actually come from.

Ember Hollow is a design and teaching tool. Check your local licensing and power rules before transmitting.