ESP32-S3 continuous servo tuning adapter for End-Fed Half-Wave antennas. Outdoor, bias-tee coaxial powered, WiFi WebSocket controlled, 100W PEP, 40m–10m full band coverage. Deeply integrated with the MRRC remote radio ecosystem.
The third-generation auto-tuner replaces relay banks with continuous servo tuning, delegates SWR sensing to MRRC/ATR1000, and adds WiFi for full remote control — all while reducing failure points from 9 to 2.
MG996R servo motor driven by ESP32-S3 LEDC PWM at 50Hz. Air variable capacitor (10–500pF) provides precise, continuous capacitance — no discrete relay steps, no dead zones.
240MHz dual-core Xtensa LX7 with 16MB flash. Five FreeRTOS tasks orchestrate tuning, WiFi communication, health monitoring, NVS persistence, and servo control in parallel.
13.8V DC rides on the same coax carrying RF and control data. No separate power cable to the outdoor unit — a single RG-58 or equivalent coax does everything.
Multi-layer protection: overpower abort at 120W threshold, high SWR protection via remote ATR1000 sensing, 2.2MΩ ESD bleed resistor, and continuous health monitor with watchdog timer.
Proven parallel LC resonant circuit design. T200-6 Type 6 carbonyl iron toroid (μ=8) with 2:14 turns ratio for 49:1 impedance transformation. Continuous capacitor replaces fixed/switched banks.
WebSocket protocol connects directly to MRRC server. SWR measurement offloaded to ATR1000 for precision. MRRC Web UI provides full ATU control panel — manual tune, band scan, cache management.
Three physical planes — indoor shack, outdoor ATU, and antenna — connected by a single coaxial cable.
Comprehensive antenna theory, transformer design, core material analysis, and practical build guides — 17 chapters of engineering research.
Also available: T200-2 Engineering Guide · ATU Architecture (Premium)
Each iteration reduced complexity while adding capability — from 9 failure points down to 2.
| V1.0 (Archived) | V2.0 (Archived) | V3.0 (Current) | |
|---|---|---|---|
| MCU | PIC16F1938 | STM32F103 | ESP32-S3 |
| Toroid | T200-2 ×2 | T200-2 ×2 | T200-6 ×1 |
| Capacitor | 7 relays / 128 steps | 7 relays / 128 steps | Servo continuous 10–500pF |
| SWR Sensing | On-board Tandem Match | On-board Tandem Match | Remote ATR1000 |
| Communication | Serial UART | Serial UART | WiFi WebSocket |
| Failure Points | 9 | 9 | 2 |
| BOM Cost | ~¥375 | ~¥390 | ~¥430 |
Open source hardware and firmware — build, flash, deploy, and tune in four steps.
Order parts from the BOM — all available on Taobao/JLC. Total cost ~¥430.
BOM: T200-6 toroid, ESP32-S3-WROOM-1, MG996R servo, air variable cap 10-500pF, IP66 enclosure
Clone the repo, configure WiFi credentials, build and flash with ESP-IDF v5.x.
git clone https://github.com/cheenle/efhw-knowledge && cd auto-efhw-tuner/firmware-esp32 && idf.py build flash
Connect coax from your shack bias-tee to the ATU. The ATU joins your WiFi and registers with MRRC.
Single coax: Bias-T (indoor) → RG-58 → ATU (outdoor) → EFHW antenna wire
Use the MRRC Web UI ATU panel — select a band, trigger auto-tune, and the servo finds optimal SWR in seconds.
MRRC → ATU Panel → Select Band → Auto-Tune → <10s → On Air
EFHW Fuchs ATU V3.0 — complete hardware and firmware specs.
| Parameter | Value |
|---|---|
| MCU | ESP32-S3-WROOM-1 (240MHz dual-core, 16MB Flash) |
| Frequency Range | 40m–10m (7–30MHz, full WARC coverage) |
| Power Rating | 100W PEP SSB/CW |
| Toroid Core | T200-6 (Type 6 carbonyl iron, μ=8) |
| Turns Ratio | 2:14 → 49:1 impedance transformation |
| Capacitor | Air variable 10–500pF, MG996R servo-driven |
| Tuning Method | Two-phase scan: 37 coarse (5°) + 30 fine (1°) |
| Tuning Time | <10s full scan, <1s NVS cache hit |
| Communication | WiFi 2.4GHz WebSocket to MRRC server |
| SWR Sensing | Remote via ATR1000 (no on-board SWR bridge) |
| Power Supply | 13.8V DC via bias-tee on coax |
| Protection | IP66 aluminum enclosure, overpower abort, high SWR abort, 2.2MΩ ESD bleed, watchdog |
| PCB | 140×50mm double-layer (KiCad), off-board RF/HV wiring |
| BOM Cost | ~¥430 (all components via Taobao/JLC) |
| Firmware | ESP-IDF v5.x C, ~2800 lines, 12 source files |
| License | Hardware: CERN-OHL-S 2.0 · Firmware: GPL-3.0 |
SDD, FDE, reference designs, and community comparison.