================================================================================ 2-ELEMENT PHASED ARRAY RDF — TM-ADF-003 Rev A Switched-Phase Cardioid Direction Finding HF/VHF Coverage with Varactor Phase Control ================================================================================ PRINCIPLE OF OPERATION ======================== Two verticals spaced λ/4 apart. By adjusting the phase of one element, the combined pattern becomes a cardioid (heart-shaped) with a deep null pointing away from the desired signal direction. 0° phase: cardioid with null pointing WEST, peak pointing EAST +90° phase: cardioid null pointing NORTH, peak pointing SOUTH etc. Bearing = direction of the MINIMUM (null) signal + 180° (null points away from transmitter; cardioid peak faces transmitter) Cardioid pattern: G(θ) = 1 + cos(θ - φ) where φ = phase shift applied and θ = angle from array axis. Null at θ = φ + 180°, peak at θ = φ. ================================================================================ SYSTEM BLOCK DIAGRAM ================================================================================ Element A (Reference) Element B (Phase shifted) λ/4 vertical λ/4 vertical │ │ │ 50Ω coax │ 50Ω coax ▼ ▼ ┌────────────────────────────────────────────────────────────────────────┐ │ 2-ELEMENT COMBINING NETWORK │ │ │ │ A ─────────────────────────────────────────────────────────────────► │──▶ SUM output │ │ │ B ──▶ [Variable Phase Shifter 0°–360°] ──────────────────────────► │──▶ (combined) │ Varactor BB112 + L network │ │ Vcontrol = 0–3.3V from DAC GPIO25 │ │ │ │ Combined ──▶ [Power Combiner Wilkinson] ──▶ 50Ω output │ └────────────────────────────────────────────────────────────────────────┘ │ ▼ ┌──────────────────────┐ │ AD8307 LOG AMP │ RSSI: 0–3.3V = −75 dBm to +12 dBm │ 50 dB dynamic range │ Slope: 25 mV/dB │ 100 mV/decade │ └──────────┬────────────┘ │ ▼ ADC GPIO35 (ESP32) ┌──────────────────────┐ │ ESP32 CONTROLLER │ │ Sweep phase 0–360° │ │ Find minimum RSSI │ │ Bearing = null + 180│ └──────────────────────┘ ================================================================================ VARACTOR PHASE SHIFTER CIRCUIT ================================================================================ Control voltage ─── GPIO25 (ESP32 DAC) ──── 0–3.3V ┌───────────────────────────────────────────────────┐ │ VARACTOR PHASE SHIFTER │ │ │ V_ctrl ──[10kΩ]──┤ ┌──── L1 ────┬─── RF out │ │ │ 82nH │ │ │ BB112 ──────┘ │ │ RF in ───────────┤ (varactor) BB112 ──┘ │ │ | | (varactor) │ │ GND GND │ │ │ │ L1 = 82nH (for 40m: ω₀ ≈ 45 MHz, tune lower) │ │ Varactor C range: 2–20 pF (BB112) │ │ Phase shift: ≈ 0–180° over varactor range │ │ For 0–360°: use two-stage design or SPDT relay │ └───────────────────────────────────────────────────┘ TWO-STAGE 0–360° DESIGN: Stage 1: varactor gives 0–180° Stage 2: SPDT relay adds fixed 180° when needed RELAY control: GPIO27 → ULN2003A → 12V relay coil VARACTOR TUNING TABLE (BB112): ┌──────────────┬─────────────────┬──────────────────────────────────┐ │ Control V │ Capacitance │ Phase (approximate, 14 MHz) │ ├──────────────┼─────────────────┼──────────────────────────────────┤ │ 0.3V │ 18 pF │ 165° │ │ 0.5V │ 16 pF │ 150° │ │ 1.0V │ 12 pF │ 120° │ │ 1.5V │ 9 pF │ 90° │ │ 2.0V │ 7 pF │ 65° │ │ 2.5V │ 5 pF │ 45° │ │ 3.0V │ 4 pF │ 30° │ │ 3.3V │ 3 pF │ 20° │ └──────────────┴─────────────────┴──────────────────────────────────┘ NOTE: Re-calibrate for each band. Reactance changes with frequency. ================================================================================ WILKINSON POWER COMBINER ================================================================================ Combines two 50Ω inputs to one 50Ω output, with isolation between ports. Input A ──────[λ/4 transmission line, 70.7Ω]──────┬──── Output 50Ω │ Input B ──────[λ/4 transmission line, 70.7Ω]──────┘ │ 100Ω (2× 50Ω) isolation resistor between inputs For HF bands: replace λ/4 lines with LC equivalents: 70.7Ω quarter-wave → L = 70.7/(2πf) Henry, C = 1/(70.7 × 2πf) Farad SWITCHED BEAM (4-position discrete): Instead of continuous phase sweep, use 4 DPDT relays for 4 beam directions: ┌──────────────────────────────────────────────────────────────────────┐ │ Relay 1: 0° phase → beam toward EAST, null toward WEST │ │ Relay 2: 90° phase → beam toward SOUTH, null toward NORTH │ │ Relay 3: 180° phase → beam toward WEST, null toward EAST │ │ Relay 4: 270° phase → beam toward NORTH, null toward SOUTH │ │ │ │ Compare RSSI at all 4 positions → null = direction AWAY from TX │ │ Peak = direction TOWARD TX (2 positions have ambiguity) │ └──────────────────────────────────────────────────────────────────────┘ ================================================================================ RSSI MEASUREMENT — AD8307 LOG AMPLIFIER ================================================================================ RF in (from combiner output, 50Ω) │ ▼ ┌────────────────────────────────────────────────────────────────┐ │ AD8307 LOG AMP (Analog Devices) │ │ │ │ Pin 1 (INP+) ──── 100pF ──── RF input │ │ Pin 8 (INM-) ──── GND │ │ Pin 4 (OUT) ──────────────────────────────────────────────► │──▶ ADC GPIO35 │ Pin 7 (VPS) ──── +5V │ │ Pin 3 (COM) ──── GND │ │ │ │ Dynamic range: −75 dBm to +12 dBm (87 dB total) │ │ Output slope: 25 mV/dB │ │ Output range: 0.1V to 2.5V for full input range │ │ Frequency: DC to 500 MHz │ │ │ │ Supply bypass: 100nF + 10µF between Pin 7 and GND │ │ Input bypass: 0.1µF in series with RF input for DC blocking │ └────────────────────────────────────────────────────────────────┘ ADC reading → dBm conversion: dBm = (ADC_voltage - 0.1) / 0.025 - 75 + calibration_offset ================================================================================ 2-ELEMENT ARRAY ELEMENT SPACING TABLE ================================================================================ ┌──────────┬────────────┬───────────────┬───────────────────────────────┐ │ Band │ Freq (MHz) │ λ/4 spacing │ Notes │ ├──────────┼────────────┼───────────────┼───────────────────────────────┤ │ 160m │ 1.85 │ 40.5 m │ Requires large field │ │ 80m │ 3.75 │ 20.0 m │ Manageable portable │ │ 40m │ 7.15 │ 10.5 m │ Good portable option │ │ 30m │ 10.125 │ 7.4 m │ │ │ 20m │ 14.175 │ 5.3 m │ │ │ 17m │ 18.118 │ 4.1 m │ │ │ 15m │ 21.225 │ 3.5 m │ │ │ 12m │ 24.940 │ 3.0 m │ │ │ 10m │ 28.850 │ 2.6 m │ Compact portable │ │ 6m │ 52.000 │ 1.4 m │ │ │ 2m │ 146.000 │ 0.51 m │ Very compact │ └──────────┴────────────┴───────────────┴───────────────────────────────┘ ================================================================================ AMBIGUITY RESOLUTION (2-element: 2 solutions 180° apart) ================================================================================ Problem: cardioid gives one null → direction is X or X+180° Solution: compare signal strength at two nearby beam positions Step 1: Find null direction θ_null (RSSI minimum) Step 2: Steer beam to θ_null + 90° and θ_null - 90° Step 3: If RSSI(+90°) > RSSI(-90°), transmitter is at θ_null + 180° If RSSI(-90°) > RSSI(+90°), transmitter is at θ_null This 3-step comparison resolves the 180° ambiguity without a sense antenna. ================================================================================ ESP32 PIN ASSIGNMENTS — 2-ELEMENT ARRAY ================================================================================ GPIO Function Notes ──── ─────────────── ────────────────────────────────────────── 25 PHASE_DAC Varactor control voltage 0–3.3V 27 RELAY_180 DPDT relay for +180° phase switch 35 RSSI_ADC AD8307 output, ADC1_CH7 21 SDA / 22 SCL I2C (OLED + compass) 16 GPS_RX / 17 TX UART GPS 2 BT_LED Bluetooth status