================================================================================ WATSON-WATT HF RDF SYSTEM — TM-ADF-001 Rev A Automatic Direction Finding, HF Bands 1.8–54 MHz Adcock / Watson-Watt Technique ================================================================================ SYSTEM BLOCK DIAGRAM ===================== N Element S Element E Element W Element (λ/4 vert) (λ/4 vert) (λ/4 vert) (λ/4 vert) │ │ │ │ │ Phase-matched │ │ Phase-matched │ │ coax (equal │ │ coax (equal │ │ electrical len)│ │ electrical len)│ ▼ ▼ ▼ ▼ ┌─────────────────────────────────────────────────────────────────┐ │ CENTRAL JUNCTION BOX │ │ │ │ N────┐ E────┐ │ │ ├──▶ BALUN (N-S) ──▶ LNA ─────▶ RF_SW port 0 ──▶ ADC0 │ │ S────┘ (FT-50-43 bifilar) │ │ │ ├──▶ RF_SW port 1 ──▶ ADC1 │ │ E────┐ │ │ │ ├──▶ BALUN (E-W) ──▶ LNA ──────┘ │ │ W────┘ │ │ │ │ SENSE────────────────────────▶ BUFFER AMP ──▶ ADC2 │ │ (omni vertical) │ └─────────────────────────────────────────────────────────────────┘ │ ESP32 ADC (bearing calc) │ ┌───────────┴───────────┐ OLED display BT / WiFi (bearing compass) (to CYD) ================================================================================ ADCOCK ARRAY ELEMENT LAYOUT (Top View) ================================================================================ N Element ▲ │ Spacing = λ/4 │ (see band table) │ W Element ◄────────────────┼────────────────► E Element │ │ ▼ S Element SENSE (omni) at center ELEMENT SPACING TABLE: ┌──────────┬────────────┬──────────────┬─────────────────────────┐ │ Band │ Freq (MHz) │ λ (m) │ λ/4 spacing (m) │ ├──────────┼────────────┼──────────────┼─────────────────────────┤ │ 160m │ 1.85 │ 162.2 │ 40.5 (full-size: 81m!) │ │ 80m │ 3.75 │ 80.0 │ 20.0 │ │ 60m │ 5.35 │ 56.1 │ 14.0 │ │ 40m │ 7.15 │ 41.9 │ 10.5 │ │ 30m │ 10.125 │ 29.6 │ 7.4 │ │ 20m │ 14.175 │ 21.2 │ 5.3 │ │ 17m │ 18.118 │ 16.6 │ 4.1 │ │ 15m │ 21.225 │ 14.1 │ 3.5 │ │ 12m │ 24.940 │ 12.0 │ 3.0 │ │ 10m │ 28.850 │ 10.4 │ 2.6 │ │ 6m │ 52.000 │ 5.8 │ 1.4 │ └──────────┴────────────┴──────────────┴─────────────────────────┘ NOTE: For portable use, reduced aperture arrays (λ/8 or λ/10) sacrifice some gain but remain usable. Bearing accuracy degrades ~3× for λ/10 spacing. ================================================================================ BALUN CIRCUIT (N-S PAIR) — Repeat for E-W Pair ================================================================================ N element ──────────────────────────────────┐ (via phase-matched coax) │ │ S element ──────────────────────────────────┤ (via phase-matched coax, reversed polarity) │ ▼ ┌────────────────────────────┐ │ CURRENT-BALUN TRANSFORMER│ │ Core: FT-50-43 toroid │ │ Winding: 10T bifilar │ │ Wire: AWG 26 enameled │ │ │ │ N ──┐ │ │ ├──▶ primary wdg │ │ S ──┘ (connected diff) │ │ │ │ Output: balanced → 50Ω │ │ unbalanced via 4:1 ratio │ └──────────┬─────────────────┘ │ 50Ω unbalanced ▼ ┌────────────────────────────┐ │ LNA — GALI-84 (MAR series)│ │ Supply: +5V @ 65mA │ │ Gain: +20 dB │ │ NF: 2.7 dB │ │ P1dB: +17 dBm │ │ │ │ IN ─────[GALI-84]───── OUT │ │ 50Ω 50Ω │ │ │ │ │ RFC RFC│ │ 100µH 47Ω│ │ │ │ │ +5V GND│ └──────────┬─────────────────┘ │ (to RF switch) BALUN WINDING DETAIL: - Core: Amidon FT-50-43 (1.27cm OD, Mix 43 ferrite) - Wind 10 turns bifilar: both wires twisted together, wound as one - One winding = N input, other winding = S input (in series opposition) - Differential voltage on primary → single-ended on secondary - Impedance ratio: 1:1 (50Ω to 50Ω for same-impedance elements) - Useful HF range: 1–30 MHz with Mix 43 ================================================================================ RF SWITCH CIRCUIT — SP4T SELECTION ================================================================================ ┌──────────────────────────────────────────┐ │ SP4T RF SWITCH │ │ PE4259 or HMC253 SPDT×2 │ │ │ From N-S LNA ──┤ Port 1 │ │ CTRL A ───────── GPIO16 (ESP32) │ From E-W LNA ──┤ Port 2 SWITCH CTRL B ──────── GPIO17│ │ LOGIC │ From SENSE ───┤ Port 3 +VDD ── 3.3V +VDD ── 3.3V │ │ │ │ (spare) ──┤ Port 4 0.1µF │ │ │ │ │ Common ──────────┼───────────────────────►│── to ADC └──────────────────────────────────────────┘ CTRL A CTRL B SELECTED PORT 0 0 Port 1 (N-S) 0 1 Port 2 (E-W) 1 0 Port 3 (SENSE) 1 1 Port 4 (spare) NOTE: PE4259 handles up to +20 dBm, suitable for RDF signal levels. Insert PE4259 between balun/LNA output and ESP32 ADC input chain. ================================================================================ SIGNAL CONDITIONING AND ADC INPUT ================================================================================ From RF switch ──────────────────────────────────────────────────────────────┐ (selected antenna pair, 50Ω) │ │ ┌─────────────────────────────────────────────────────────────────────────┐ │ │ AUDIO IF STRIP │◄─┘ │ │ │ [50Ω input]──[BPF, 300-3000 Hz]──[INA128 Instrumentation Amp]────── │ │ (audio band) Gain = 60 dB │ │ RG = 56Ω (sets gain) │ │ │ │ ...──[Envelope Detector]──[RC filter 10ms]──[ADC Buffer]──────────── │ │ (peak detector) (smoothing) (voltage follower) │ │ BAT46 + 10kΩ + 10µF LMV321 rail-rail op-amp │ │ │ │ Output ── ESP32 ADC1_CH0 (GPIO34) ── 0–3.3V signal level │ └─────────────────────────────────────────────────────────────────────────┘ COMPONENT VALUES: ┌─────────────────┬────────────────────────────────────────────────────┐ │ Component │ Value / Part │ ├─────────────────┼────────────────────────────────────────────────────┤ │ INA128 │ Instrumentation amp, Burr-Brown / TI │ │ R_gain │ 56Ω → G = 1 + 50000/56 = 893 ≈ 60 dB │ │ C_in (bypass) │ 100nF ceramic, 0805 │ │ C_supply │ 100µF + 100nF on ±5V supply rails │ │ Envelope diode │ BAT46 Schottky, Vf = 0.2V │ │ R_env │ 10kΩ (discharge, τ = 10ms with C_env) │ │ C_env │ 1µF (smoothing capacitor) │ │ Buffer amp │ LMV321 single-supply (0–3.3V operation) │ └─────────────────┴────────────────────────────────────────────────────┘ ================================================================================ POWER SUPPLY ================================================================================ External: 12V DC input (2.1mm barrel jack, center positive) 12V ──┬──[LM7805]──── +5V ──┬── LNA bias (via 47Ω + bypass) │ └── INA128 V+, relay coils │ └──[AMS1117-3.3]─── +3.3V ──── ESP32, ADC refs, RF switch control Current budget: ESP32 module: ~250 mA (WiFi active) 2× LNA GALI-84: 2 × 65 mA = 130 mA INA128: 1 mA RF switch: 5 mA OLED: 20 mA Total: ~410 mA from 5V rail, 70 mA from 3.3V rail 12V supply minimum: 600 mA (use 1A regulated supply) ================================================================================ BEARING CALCULATION — WATSON-WATT ALGORITHM ================================================================================ 1. Sample N-S pair for T milliseconds → compute RMS amplitude: V_NS 2. Switch to E-W pair → compute RMS amplitude: V_EW 3. Switch to SENSE → compute RMS amplitude: V_SENSE Raw bearing (uncorrected): θ = atan2(V_NS, V_EW) [returns –90° to +90°] Four-quadrant resolution (use signs of V_NS and V_EW): θ_4q = atan2(signed_V_NS, signed_V_EW) [–180° to +180°] θ_4q_normalized = (θ_4q + 360°) mod 360° [0° to 360°] Ambiguity (two solutions 180° apart): Test bearing θ and θ+180° Add sense to each: S1 = V_NS + V_SENSE, S2 = V_NS - V_SENSE Correct bearing: the one where sense INCREASES (reinforces) the signal Calibration: Apply N-S gain correction K_NS and E-W gain correction K_EW (measured by placing transmitter at known bearing, then adjusting until atan2 gives correct angle) Also apply phase correction φ for cable electrical length differences ================================================================================ ESP32 PIN ASSIGNMENTS SUMMARY ================================================================================ GPIO Function Notes ──── ───────────── ───────────────────────────────────────── 34 NS_ADC ADC1_CH6, signal level N-S pair 35 EW_ADC ADC1_CH7, signal level E-W pair 32 SENSE_ADC ADC1_CH4, sense antenna level 16 RF_SW_A RF switch control bit 0 17 RF_SW_B RF switch control bit 1 18 RF_SW_EN Switch enable (active low) 21 SDA I2C: OLED + QMC5883L compass 22 SCL I2C clock 18 GPS_RX UART2 receive from NEO-8M 19 GPS_TX UART2 transmit to GPS 5 GPS_PPS 1PPS interrupt input (rising edge) 25 AUDIO_DAC DAC output for audio monitoring 2 BT_LED Bluetooth connected indicator ================================================================================ PHASE-MATCHED COAXIAL FEED LINE REQUIREMENT ================================================================================ ALL coaxial runs from elements to central junction MUST be identical electrical length (same physical length if same VF cable used). Measurement procedure (with NanoVNA): 1. Cut one reference length of RG-58 (e.g., 10m) 2. Measure electrical length with NanoVNA TDR or phase at the target frequency 3. Cut all 5 feed lines (N, S, E, W, SENSE) to the SAME electrical length 4. Tolerance: ±5mm physical for RG-58 (VF=0.66) → ±1° phase error at 30 MHz Cable suggestion: RG-58 (VF=0.66), or LMR-195 for lower loss on longer runs. For portable operation: limit element runs to 10m maximum per side.