================================================================================ SCHEMATIC: Relay-Based Remote Antenna Switch TM-ANT-SW-001 Rev A ESP32-Controlled, 4-Port and 8-Port Designs HF through 450 MHz | Power: 1 kW CW / 2 kW PEP | IL < 0.2 dB to 450 MHz Remote Control via WiFi/Web, UART, or DC voltage ================================================================================ RELAY SELECTION THEORY ─────────────────────── Standard electromechanical relays (signal relays, power relays) are NOT suitable for RF coaxial switching. The contact geometry is wrong, the isolation is poor, and the RF path is not controlled-impedance. Proper coaxial relay design uses one of these approaches: APPROACH 1 — PURPOSE-BUILT COAXIAL RELAY (best): Relays designed specifically for coaxial signal switching. Center conductor passes through controlled-impedance path. Examples: Tohtsu CX-110D, Dow-Key 401-125, Teledyne RFR series. Cost: $15–$80 per relay. IL < 0.1 dB through 2 GHz. APPROACH 2 — GOOD-QUALITY SPDT RELAY WITH COAXIAL PCB LAYOUT (budget): Use high-isolation relay (Omron G2RL, Panasonic TQ2, or equiv.) Mount on 50Ω microstrip PCB. Route center conductor as 50Ω trace. Add metal shields between relay positions. Cost: $1–$5 per relay. IL 0.05–0.2 dB at 150 MHz; degrades above 300 MHz. APPROACH 3 — LATCHING RELAY (power-saving): Latching relays hold position without continuous coil current. Important for battery-powered remote switches. Doubles set/reset coil cost; requires H-bridge drive circuit. Examples: Omron G2RK, Panasonic TQ2-L. This design uses APPROACH 2 for the budget 4-port version and includes APPROACH 1 specifications for the VHF-capable version. ================================================================================ RELAY SPECIFICATIONS — BUDGET HF VERSION ================================================================================ OMRON G2RL-1A4-E-TV8 (recommended budget relay): Coil: 12V DC, 400 mW (33mA) Contact: SPDT, 16A at 250VAC Contact material: silver alloy Isolation when open (10 MHz, measured): > 60 dB typical Operate time: < 10 ms Release time: < 5 ms Mechanical life: 10 million operations Footprint: through-hole, 5-pin ALTERNATIVE — PANASONIC TQ2-12V: Coil: 12V DC, 200 mW (16.7mA) Contact: DPDT (can use both contact sets for additional isolation) Contact rating: 2A at 220VAC (lower — adequate for RF, not power switching) Isolation (14 MHz): > 65 dB COAXIAL RELAY (VHF SPEC) — TOHTSU CX-110D: Frequency: DC to 500 MHz IL: < 0.1 dB to 500 MHz Isolation: > 60 dB to 500 MHz Power: 1kW at HF, 500W at 500 MHz Coil: 12V, 320 mW Connectors: SO-239 (CX-110D) or N-type (CX-110DN) ================================================================================ 4-PORT RELAY SWITCH — SCHEMATIC ================================================================================ SWITCHING TOPOLOGY: Three SPDT relays, binary-tree configuration. For 4 ports from 1 common: - 3 relays needed: K1 (main splitter), K2 (low pair), K3 (high pair) - This uses fewer relays than one relay per port - Insertion path uses 2 relay contacts in series (slightly higher IL) BINARY TREE TOPOLOGY: ANT1 ──────────────────── K2 NO ──┐ │ K2 ────┤ COM │ ANT2 ──────────────────── K2 NC ──┘─── K1 NO ──┐ │ K1 ───┤ COM │──── COMMON (Radio) ANT3 ──────────────────── K3 NO ──┐ │ │ │ K3 ────┤ │ COM │ │ ANT4 ──────────────────── K3 NC ──┘─── K1 NC ──┘ SELECTION TABLE: K1=0, K2=0 → ANT1 (K1=NC selects "high pair"; K2=NC selects ANT1 or ANT2) Wait — let me clarify: When relay is DE-ENERGIZED (coil off): COM connects to NC (normally closed) When relay is ENERGIZED (coil on): COM connects to NO (normally open) K1 de-energized (0): routes through K2 K1 de-energized (0), K2 de-energized (0): → ANT1 (K2 NC path → ANT1) K1 de-energized (0), K2 energized (1): → ANT2 (K2 NO path → ANT2) K1 energized (1): routes through K3 K1 energized (1), K3 de-energized (0): → ANT3 (K3 NC path) K1 energized (1), K3 energized (1): → ANT4 (K3 NO path) K1 | K2 | K3 | Selected ---|----|----|-------- 0 | 0 | x | ANT 1 0 | 1 | x | ANT 2 1 | x | 0 | ANT 3 1 | x | 1 | ANT 4 ALTERNATIVE TOPOLOGY — ONE RELAY PER PORT (simpler; more relays; single contact): For 4 ports: 4 relays, one in each antenna path. Only the selected relay is energized; all others open. Selected path: signal flows through NO contact of one relay only. IL: single relay contact in path (lower IL). Relay count: N relays for N ports (vs. N-1 for binary tree). COMMON ───────────────────────────────────────────────── │ │ │ │ [K1] [K2] [K3] [K4] │ │ │ │ ANT1 ANT2 ANT3 ANT4 Interlocking logic (firmware): only one relay energized at a time. THIS DESIGN USES: ONE RELAY PER PORT (simpler PCB, better IL, preferred for N≤8) ================================================================================ 4-PORT SWITCH — COMPLETE CIRCUIT WITH ESP32 CONTROL ================================================================================ POWER SUPPLY AND RELAY DRIVER: 12V DC INPUT ──┬────────────────────────────────── +12V rail │ [100µF] (bulk decoupling) [0.1µF] (RF bypass) │ GND RELAY DRIVE CIRCUIT (per relay, 4× identical): ESP32 GPIO ──[10kΩ pull-down]──┬──[100Ω]── Base of 2N2222A (or MMBT2222A SMD) │ GND │ Collector ──[1N4007]── +12V (flyback) │ RELAY COIL (K1–K4) │ +12V NPN transistor in switch configuration: GPIO HIGH (3.3V) → transistor saturates → relay energizes GPIO LOW (0V) → transistor cuts off → relay releases 2N2222A: V_CEO = 40V, I_C = 600mA (relay coil 33mA — well within rating) Base resistor 100Ω limits I_B = (3.3V - 0.7V) / 100Ω = 26mA → hFE×I_B >> I_C ✓ Flyback diode 1N4007 clamps coil back-EMF (up to 50V spike without diode) RELAY DRIVER BLOCK DIAGRAM: ESP32 ULN2003A (7× Darlington array, alternative to discrete) GPIO26 ──[150Ω]── IN1 ── OUT1 ──────────────────── RELAY K1 coil GPIO27 ──[150Ω]── IN2 ── OUT2 ──────────────────── RELAY K2 coil GPIO14 ──[150Ω]── IN3 ── OUT3 ──────────────────── RELAY K3 coil GPIO12 ──[150Ω]── IN4 ── OUT4 ──────────────────── RELAY K4 coil GPIO25 ──[150Ω]── IN5 ── OUT5 ──────────────────── LED STATUS (3.3V logic) GPIO33 ──[150Ω]── IN6 ── OUT6 ──────────────────── LED STATUS COM ──────────────────────────── +12V (relay coil supply) ULN2003A internal structure: each channel is a Darlington pair + flyback diode Rated: 500mA per channel, 50V; suppression diodes included. Single IC replaces 7 discrete transistors + diodes. STATUS INDICATOR LEDs (4 port LEDs + 1 power LED): +3.3V ──[470Ω]──[LED_PWR]── GND (power on indicator; always lit) For each antenna port (1–4): ESP32 GPIO ──[470Ω]──[LED_ANTn]── GND LED lights when port is SELECTED (relay energized). LED COLOR CONVENTION: ANT 1: Green ANT 2: Yellow ANT 3: Blue ANT 4: Red POWER: White or Green RF PATH (4-Port): COMMON ──[SO-239]────────────────────────────────────────────────── │ │ +──────┤ center conductor │ │ │ chassis/ground [RELAY K1] │ COM ─── NO ─────┴─── ANT1 center ──[47kΩ to gnd]──[SO-239]── ANT1 │ NC ─ (open/unused via when K1 selected) NOTE: All four relays are separate; center conductor routes from COMMON to one selected antenna. All connector outers share chassis ground. Each relay: COM = connected to COMMON port center conductor via 50Ω trace NO = connected to one ANT port center conductor NC = not connected (open, with 47kΩ static drain to chassis on each ANT port) COMPLETE PIN ASSIGNMENT (ESP32): Function | GPIO | Notes -------------------|------|----------------------------------------------- Relay K1 (ANT 1) | 26 | via ULN2003A Relay K2 (ANT 2) | 27 | via ULN2003A Relay K3 (ANT 3) | 14 | via ULN2003A Relay K4 (ANT 4) | 12 | via ULN2003A LED ANT1 | 25 | 470Ω series resistor LED ANT2 | 33 | 470Ω series resistor LED ANT3 | 32 | 470Ω series resistor LED ANT4 | 35 | input only — use external LED driver Button ANT1 | 4 | pull-up, active low Button ANT2 | 5 | pull-up, active low Button ANT3 | 18 | pull-up, active low Button ANT4 | 19 | pull-up, active low CYD TFT CS | 15 | SPI CYD TFT DC | 2 | SPI CYD TFT RST | - | tied to 3.3V via 10kΩ, cap to GND CYD Touch CS | 33 | SPI (if using separate touch SPI) UART TX (band data)| 17 | to band data decoder UART RX (band data)| 16 | from transceiver band data ================================================================================ 8-PORT RELAY SWITCH — EXTENSION ================================================================================ For 8 ports, add four more relays (K5–K8) and a second ULN2003A. ESP32 GPIO 23, 22, 21, 19 → ULN2003A-2 IN1–IN4 → Relays K5–K8 LEDs: use 74HC595 shift register to expand outputs (1 GPIO → 8 LEDs) 74HC595 LED DRIVER (serial-in, parallel-out): ESP32 GPIO ── SER (14) ── QA–QH ── [LED 1–8] via 470Ω resistors ESP32 GPIO ── SRCLK (11) ESP32 GPIO ── RCLK (12) VCC = 3.3V or 5V GND ================================================================================ POWER BUDGET ================================================================================ Relay coil current (per relay, 12V): Omron G2RL: 400 mW / 12V = 33 mA per relay Panasonic TQ2: 200 mW / 12V = 17 mA per relay Worst case (all relays energized briefly during switch transition): 4× G2RL: 4 × 33 mA = 132 mA + ESP32 (200 mA) + LEDs (40 mA) = ~375 mA at 12V Normal (1 relay energized): 33 + 200 + 10 = 243 mA Power supply: 12V, 1A minimum. Use 12V/2A for margin. For battery operation: use latching relays (Omron G2RK-L). Latching relay current: pulse only (< 10 ms to set/reset). Standby current: ESP32 light-sleep 0.8 mA + LED 10 mA = ~11 mA @ 12V ================================================================================ PARTS LIST — RELAY REMOTE SWITCH ================================================================================ Item | Qty | Description | Source -------|-----|------------------------------------------|------------------- K1-K4 | 4 | Omron G2RL-1A4-E-TV8 (12V SPDT) | Mouser K_VHF | 4 | Tohtsu CX-110D (VHF-rated coax relay) | DX Eng., RF Parts ULN | 1 | ULN2003A 7-channel Darlington driver | Mouser ESP32 | 1 | ESP32-WROOM-32 module or DOIT DevKit | Mouser CYD | 1 | ESP32-2432S028 (CYD 2.8" TFT) | AliExpress REG | 1 | LM7805 or AMS1117-3.3 (ESP32 supply) | Mouser CAP1 | 1 | 100µF 25V electrolytic (relay decoup) | Mouser CAP2 | 4 | 0.1µF ceramic (relay bypass) | Mouser R1-R4 | 4 | 150Ω 1/4W (ULN input; one per ch) | Mouser R_LED | 8 | 470Ω 1/4W (LED current limit) | Mouser R_GND | 4 | 47kΩ 1/4W (static ground per ANT port) | Mouser LED | 5 | 3mm/5mm LED: green, yel, blue, red, wht | Mouser BTN | 5 | 6mm tactile switch (4 ANT + 1 prev/next)| Mouser CONN | 5 | SO-239 silver panel mount | Amphenol J_12V | 1 | 2.1mm barrel jack (power input) | Mouser PCB | 1 | Custom or perf board, ground plane | JLCPCB ENCL | 1 | Die-cast Al 160×100×40mm, IP54 | Hammond 1590B2 ================================================================================