================================================================================ SWITCHED DIRECTIONAL ANTENNA ARRAY WITH DELAY LINES — TM-ADF-006 Rev A 4-Element Switched Array, Calculated Delay Lines HF Bands 160M through 6M ================================================================================ PRINCIPLE OF OPERATION ======================== Four verticals arranged in a square (λ/4 per side). By introducing calibrated electrical delay (coaxial delay lines) between adjacent elements and summing them in phase, a cardioid pattern is formed pointing in the desired direction. When element signals are combined with relative delays of 0°, 90°, 180°, 270° (one per element, increasing around the array), the result is an endfire pattern with a deep null pointing away from the intended direction. FOUR BEAM POSITIONS by delay assignment: ┌──────────────┬──────────────────────────────────────────────────────────┐ │ Beam Dir │ Delay on E1(N) E2(E) E3(S) E4(W) │ ├──────────────┼──────────────────────────────────────────────────────────┤ │ NORTH (peak) │ 0° 90° 180° 270° │ │ EAST (peak) │ 270° 0° 90° 180° │ │ SOUTH (peak) │ 180° 270° 0° 90° │ │ WEST (peak) │ 90° 180° 270° 0° │ └──────────────┴──────────────────────────────────────────────────────────┘ ================================================================================ PHYSICAL ARRAY LAYOUT ================================================================================ Top view: 4 elements at corners of square, spacing = λ/4 [E1 — NORTH] │ ────●──── │ d = λ/4 ────●──── │ [E4 — WEST] ─── d ───●─── d ─── [E2 — EAST] │ ────●──── │ d = λ/4 ────●──── │ [E3 — SOUTH] Each element: λ/4 vertical monopole with 4× ground radials ================================================================================ DELAY LINE CALCULATIONS ================================================================================ Coaxial delay line for 90° at frequency f: Physical length L = (c × VF) / (4 × f) where c = 3×10⁸ m/s, VF = velocity factor of coax DELAY LINE LENGTH TABLE — RG-58 (VF = 0.66): ┌──────────┬────────────┬──────────┬─────────────────────────┐ │ Band │ Freq (MHz) │ 90° delay│ Notes │ ├──────────┼────────────┼──────────┼─────────────────────────┤ │ 160m │ 1.85 │ 26.8 m │ Long; use surplus coax │ │ 80m │ 3.75 │ 13.2 m │ │ │ 60m │ 5.35 │ 9.2 m │ │ │ 40m │ 7.15 │ 6.9 m │ Practical portable │ │ 30m │ 10.125 │ 4.9 m │ │ │ 20m │ 14.175 │ 3.5 m │ │ │ 17m │ 18.118 │ 2.7 m │ │ │ 15m │ 21.225 │ 2.3 m │ │ │ 12m │ 24.940 │ 2.0 m │ │ │ 10m │ 28.850 │ 1.7 m │ │ │ 6m │ 52.000 │ 0.95 m │ Very compact! │ └──────────┴────────────┴──────────┴─────────────────────────┘ EXAMPLE: 40m band, 7.15 MHz, RG-58 (VF=0.66): 90° delay = (3×10⁸ × 0.66) / (4 × 7.15×10⁶) = 6.92 m ≈ 6.9 m For NORTH beam: E1=0m, E2=6.9m, E3=13.8m, E4=20.7m of extra coax NOTE ON MULTI-BAND OPERATION: Fixed delay lines work at ONE band only. For multi-band: - Option A: switchable delay lines (relay-switched coax segments per band) - Option B: digital delay (high-speed ADC + DSP phase shift in firmware) - Option C: separate delay line boxes per band, swap as needed ================================================================================ SWITCHING RELAY CIRCUIT ================================================================================ Control: 74HC595 shift register + ULN2003A darlington driver ESP32 GPIO connections to 74HC595: GPIO16 ──── SER (serial data) GPIO17 ──── SRCLK (shift clock) GPIO18 ──── RCLK (latch clock) 74HC595 outputs Q0–Q7 ──── ULN2003A inputs ──── Relay coils (12V) RELAY MATRIX (16 relays total — 4 beams × 4 elements): ┌────────────────────────────────────────────────────────────────────────┐ │ Element E1 ──[Delay 0m relay]──────────────────────────────┐ │ │ ├──[Delay 6.9m relay]──────────────────────────┐ │ │ │ ├──[Delay 13.8m relay]────────────────────────┐ │ │ │ │ └──[Delay 20.7m relay]──────────────────────┐ │ │ │ │ │ │ │ │ │ │ │ (similar relay matrix for E2, E3, E4) │ │ │ │ │ │ │ │ │ │ │ │ Power combiner (Wilkinson 4-way) ◄─────────────────────┘─┘─┘──┘ │ │ │ │ │ ▼ 50Ω combined output ──── to receiver/RSSI │ └────────────────────────────────────────────────────────────────────────┘ SIMPLIFIED 4-POSITION RELAY BOARD: One relay selects which delay coil bundle is active: ┌──────────────────────────────────────────────────────────────────────┐ │ RELAY 1 (NORTH BEAM): routes E1=0°, E2=90°, E3=180°, E4=270° │ │ RELAY 2 (EAST BEAM): routes E1=270°, E2=0°, E3=90°, E4=180° │ │ RELAY 3 (SOUTH BEAM): routes E1=180°, E2=270°, E3=0°, E4=90° │ │ RELAY 4 (WEST BEAM): routes E1=90°, E2=180°, E3=270°, E4=0° │ │ │ │ Control: 74HC595 bit 0–3 → ULN2003A → 12V relay coils │ └──────────────────────────────────────────────────────────────────────┘ ================================================================================ 4-WAY POWER COMBINER / SPLITTER (WILKINSON) ================================================================================ Four 50Ω inputs → one 50Ω output (6dB combining loss + isolation): Two-stage binary Wilkinson tree: Stage 1: two 2-way Wilkinson combiners → two outputs Stage 2: one 2-way Wilkinson combiner → final output First 2-way combiner: E1+E2 → Combiner A → Port C Second 2-way combiner: E3+E4 → Combiner B → Port D Final combiner: C+D → Combiner C → OUTPUT Each Wilkinson stage: Input1 ──[λ/4, 70.7Ω]──┬── Output (50Ω) Input2 ──[λ/4, 70.7Ω]──┘ │100Ω isolation resistor between inputs│ PCB implementation preferred; for field use, can use T-junction with 3dB padding (lossy but simple). ================================================================================ RSSI MEASUREMENT ================================================================================ Combined output ──▶ [LNA optional, +20dB] ──▶ [AD8307 log amp] ──▶ ADC AD8307: Input: 50Ω, −75 to +12 dBm Output: 25 mV/dB linear-in-dB ESP32 ADC: GPIO35 (ADC1_CH7), 12-bit, 0–3.3V SCAN SEQUENCE (firmware): 1. Switch NORTH beam → wait 50ms → read RSSI[0] 2. Switch EAST beam → wait 50ms → read RSSI[1] 3. Switch SOUTH beam → wait 50ms → read RSSI[2] 4. Switch WEST beam → wait 50ms → read RSSI[3] 5. Peak RSSI index → bearing = index × 90° 6. Gaussian interpolation → sub-step bearing estimate ================================================================================ DELAY LINE INTERCONNECTION — 40M EXAMPLE ================================================================================ Full wiring for one band (7.15 MHz, 40m): E1 (N) ─ 50Ω coax ─── 0m delay ────────────────────────────────────┐ E2 (E) ─ 50Ω coax ─── 6.9m RG-58 ─────────────────────────────────┤ 4-way E3 (S) ─ 50Ω coax ─── 13.8m RG-58 ────────────────────────────────┤ combiner E4 (W) ─ 50Ω coax ─── 20.7m RG-58 ────────────────────────────────┘ │ ▼ NORTH BEAM OUTPUT For EAST beam: relay connects different length delay to each element: E1 ── 20.7m (270°), E2 ── 0m (0°), E3 ── 6.9m (90°), E4 ── 13.8m (180°) Each beam uses a separate pre-cut coax bundle with BNC connectors. Relay board patches correct bundle to combiner. ================================================================================ ESP32 PIN ASSIGNMENTS — SWITCHED ARRAY ================================================================================ GPIO Function Notes ──── ───────────── ────────────────────────────────────────── 16 SER 74HC595 serial data 17 SRCLK 74HC595 shift clock 18 RCLK 74HC595 latch clock 35 RSSI_ADC AD8307 output (ADC1_CH7) 21 SDA / 22 SCL I2C: OLED + compass 18* GPS_RX / 19 TX *conflict: use GPIO4/5 for GPS instead 2 BT_LED