================================================================================ COMPACT PORTABLE SWR METER - COMPLETE CIRCUIT SCHEMATICS Coverage: All 15 Ham Bands (160M through 20CM) Design: Claude Code - 2025 ================================================================================ CONTENTS ================================================================================ Section 1: Overview and Block Diagram Section 2: HF Directional Coupler (160M-10M) Section 3: VHF/UHF Directional Coupler (6M-20CM) Section 4: Diode Detector Circuits Section 5: Meter Driver Circuits Section 6: Range Switching Section 7: Section Selection (HF/VHF) Section 8: Complete Parts List Section 9: PCB Layout Guidelines Section 10: Calibration Circuits Section 11: Construction Notes SECTION 1: OVERVIEW AND BLOCK DIAGRAM ================================================================================ This SWR meter uses dual directional couplers optimized for different frequency ranges, with diode detection and analog metering. SYSTEM BLOCK DIAGRAM: ┌─────────────────────────────────────────┐ Transmitter │ │ Antenna (50Ω) │ SWR METER │ │ │ ├───────────┤ ┌──────────────────────────────────┐ ├───────── │ │ │ HF COUPLER (160M-10M) │ │ │ INPUT │ │ Tandem-Match Transmission Line │ │ OUTPUT │ SO-239 │ │ -30 dB coupling │ │ SO-239 │ │ └──────────────────────────────────┘ │ │ │ │ │ │ │ │ FWD Sample REF Sample │ │ │ │ │ │ │ │ ▼ ▼ │ │ │ ┌──────────────────────────────────┐ │ │ │ │ DIODE DETECTORS │ │ │ │ │ Schottky diodes + filters │ │ │ │ └──────────────────────────────────┘ │ │ │ │ │ │ │ │ DC_FWD DC_REF │ │ │ │ │ │ │ │ ▼ ▼ │ │ │ ┌──────────────────────────────────┐ │ │ │ │ METER DRIVERS │ │ │ │ │ Range switching, calibration │ │ │ │ └──────────────────────────────────┘ │ │ │ │ │ │ │ │ ▼ ▼ │ │ │ [FWD METER] [REF METER] │ │ │ or [COMBINED SWR METER] │ │ │ │ │ │ ┌──────────────────────────────────┐ │ │ │ │ VHF/UHF COUPLER (6M-20CM) │ │ │ │ │ Microstrip PCB │ │ │ │ │ -30 dB coupling │ │ │ │ └──────────────────────────────────┘ │ │ │ │ │ │ [HF/VHF Selector Switch] │ ├───────────┤ ├───────── │ │ └─────────────────────────────────────────┘ OPERATING PRINCIPLE: 1. Select HF or VHF/UHF coupler using selector switch 2. RF passes through selected coupler (main line) 3. Coupler samples forward and reflected power (coupled lines) 4. Diode detectors convert RF samples to DC voltages 5. Meter drivers scale DC voltages and drive analog meters 6. Read forward power and SWR directly from meter faces SECTION 2: HF DIRECTIONAL COUPLER (160M-10M) ================================================================================ TOPOLOGY: Tandem-Match Transmission Line Coupler This design uses two parallel transmission lines with specific coupling to achieve wideband directional performance from 1.8-30 MHz. PHYSICAL CONSTRUCTION: Main Line (Coax carrying full power): ═══════════════════════════════════════════════════════ Coupled Lines (Two parallel lines, close-coupled): ─────────────────────────────────────────────────────── ─────────────────────────────────────────────────────── │ │ FWD Sample REF Sample DETAILED SCHEMATIC: INPUT Connector OUTPUT Connector (SO-239) (SO-239) │ │ │ ╔════════════ MAIN LINE ════════════╗ │ ├─────────╢ RG-58 Coax, 50Ω, 150mm ╟─────────┤ │ ╚════════════════════════════════════════════╝ │ │ │ GND GND Coupled Line 1 (Forward sampling): ┌────────────────────────────────────────────┐ │ Twisted pair or parallel wire, 150mm │ │ Coupled to main line via proximity │ └────────────────────────────────────────────┘ │ │ │ │ ─┴─ 100pF To FWD ─┬─ (DC block) Detector │ GND Coupled Line 2 (Reflected sampling): ┌────────────────────────────────────────────┐ │ Twisted pair or parallel wire, 150mm │ │ Coupled to main line via proximity │ └────────────────────────────────────────────┘ │ │ │ │ ─┴─ 100pF To REF ─┬─ (DC block) Detector │ GND COUPLING MECHANISM: The coupled lines run parallel to the main coax for 150mm. Electromagnetic coupling between the lines causes a small fraction of the RF power to appear on the coupled lines. Forward-traveling wave on main line → voltage on FWD coupled line Reflected wave on main line → voltage on REF coupled line Directivity is achieved by the physical separation and termination of the coupled lines. CONSTRUCTION DETAILS: Main Line: - RG-58 coaxial cable, 50Ω, ~150mm effective coupling length - Or: RG-316 (smaller diameter, same impedance) - Straight run through enclosure - SO-239 connectors on each end Coupled Lines: - Method 1: Twisted pair (2 × 24 AWG) laid alongside main coax Distance: 2-3mm from coax outer conductor Twist rate: 10-15 twists per inch - Method 2: Parallel wires on PCB Trace width: 1mm, spacing 2mm Ground plane on opposite side - Method 3: Bifilar winding on ferrite rod Two wires wound together on ferrite Better low-frequency response COUPLING FACTOR: Target: -30 dB (1/1000 of main power) At 100W main line: Coupled power ≈ 0.1W (100 mW) Main line continues with 99.9W (negligible insertion loss) Adjust coupling by varying distance between coupled line and main coax: - Closer = tighter coupling (higher sample, more loss) - Farther = looser coupling (lower sample, less loss) DIRECTIVITY: Goal: >25 dB Meaning: FWD sample responds 25 dB more to forward wave than reverse wave (and vice versa for REF sample) Achieved by: 1. Physical separation of FWD and REF coupling points 2. Proper termination resistors 3. Matched line lengths TERMINATION: Each coupled line must be properly terminated: FWD Coupled Line: One end: To detector via DC blocking capacitor Other end: Terminated with 50Ω resistor to ground REF Coupled Line: One end: Terminated with 50Ω resistor to ground Other end: To detector via DC blocking capacitor The terminations absorb unwanted reflections and improve directivity. EQUIVALENT CIRCUIT (Simplified): Main Line: IN ═══════════════════════════════════════════════════ OUT ║ ║ ╔══╬══╗ ╔══╬══╗ ║Couple║ ║Couple║ ╚══╬══╝ ╚══╬══╝ ║ ║ ───────┴────────── ────────┴────────── FWD │ │ 50Ω REV │ │ 50Ω Line│ GND Line│ GND │ │ ─┴─ 100pF ─┴─ 100pF ─┬─ ─┬─ │ │ To FWD To REF Detector Detector SECTION 3: VHF/UHF DIRECTIONAL COUPLER (6M-20CM) ================================================================================ TOPOLOGY: Microstrip Directional Coupler (PCB-Based) At VHF/UHF frequencies, PCB-based couplers with controlled impedance provide excellent performance. PCB STACKUP: Top Layer: Microstrip traces (signal lines) Dielectric: FR4, 1.6mm thickness, εr = 4.5 Bottom Layer: Solid copper ground plane COUPLER LAYOUT (Top View): Input Output │ │ │ Main Line (50Ω microstrip) │ ├─══════════════════════════════════════════─┤ │ │ │ │ │ Coupled Line (50Ω microstrip, 0.5mm gap) │ ───────────────────────────────────── │ │ │ │ │ │ FWD │ REF Sample │ Sample │ 50Ω 50Ω │ Term Term GND GND MICROSTRIP DIMENSIONS: For 50Ω impedance on 1.6mm FR4 (εr = 4.5): - Trace width: 3.0mm - Trace spacing (main to coupled): 0.5mm - Coupled line length: 30mm (quarter-wave at 50 MHz) Scaling for different frequencies: λ/4 at 50 MHz (6M): 30mm λ/4 at 146 MHz (2M): 10mm λ/4 at 1296 MHz (23CM): 1.2mm Use longest length (30mm) for wideband coverage 50-1300 MHz. DETAILED SCHEMATIC: MAIN LINE (Top layer) ══════════════════════ INPUT ─────┬───╪ ╪───┬───── OUTPUT GND ║ ║ GND ║ ║ ║ Coupled Line (0.5mm gap) ║ ────────────────────── ║ │ │ ║ │ │ ▼ ▼ ▼ FWD REF Sample Sample │ │ ─┴─ 100pF ─┴─ 100pF ─┬─ ─┬─ │ │ ┌┴┐ 50Ω ┌┴┐ 50Ω │ │ Term │ │ Term └┬┘ └┬┘ │ │ GND GND COUPLING CALCULATION: Coupling factor depends on: 1. Spacing between traces 2. Trace width 3. Dielectric constant 4. Frequency For -30 dB coupling: - Gap ≈ 0.5mm - Trace width = 3mm (50Ω line) - Adjust spacing to achieve -30 dB at mid-frequency Design tools: - AppCAD (Agilent/Keysight) - free - QucsStudio - free EM simulation - Online microstrip calculators GROUND PLANE: Bottom layer must be solid copper (no breaks) for: - Return current path - Controlled impedance - Shielding Via stitching: - Add vias every 5-10mm around perimeter - Connects top ground pads to bottom ground plane - Reduces unwanted coupling TERMINATION RESISTORS: Use surface-mount resistors: - 0805 or 1206 size - 50Ω, 1%, 1/4W - Place close to coupled line ends - Short leads/traces ASSEMBLY: Components on PCB: - 4× Schottky diodes (SOT-23 or DO-35) - 4× 50Ω termination resistors (0805) - 4× 100pF DC blocking caps (0805) - 4× 100nF bypass caps (0805) - SMA or SO-239 edge-mount connectors PCB FABRICATION: Order from: - OSH Park, JLCPCB, PCBWay - Standard specs: 1.6mm FR4, 1oz copper - Cost: $10-30 for 3 boards Or DIY: - Single-sided copper-clad board - Toner transfer or photoresist - Etch with ferric chloride - Drill holes SECTION 4: DIODE DETECTOR CIRCUITS ================================================================================ Diode detectors convert RF power samples to DC voltages proportional to power level. BASIC DETECTOR CIRCUIT: From Coupler To Meter Driver (FWD or REF) │ ─┴─ C1 (DC block, 100pF) ─┬─ │ │ ┌─┐ ├────┤ │ D1 (Schottky diode) │ └─┘ │ │ ─┴─ C2│ (filter, 100nF) ─┬─ │ │ │ GND ┌┴┐ R1 (load, 10kΩ) │ │ └┬┘ │ ───→ DC output (to meter) │ GND COMPONENT SELECTION: D1 - Schottky Diode: - Type: HP2835, 1N5711, or BAT46 - Low forward voltage (0.15-0.3V) - Fast switching (important for RF) - Quantity: 2× (one for FWD, one for REF) Why Schottky? - Low Vf allows detection of low power levels - Fast response (no charge storage delay) - More linear than silicon diodes Matched Pairs: - Buy 10 diodes - Measure forward voltage drop (Vf) at 1mA - Select two with closest Vf (within 10 mV) - Use matched pair for FWD and REF - Improves accuracy! C1 - DC Blocking Capacitor: - Value: 100pF - Type: Ceramic (COG/NPO) - Voltage: 50V minimum - Function: Blocks DC from transmitter, passes RF C2 - Filter Capacitor: - Value: 100nF (0.1μF) - Type: Ceramic (X7R acceptable) - Function: Filters RF, passes DC to meter R1 - Load Resistor: - Value: 10kΩ - Type: 1/4W, 5% - Function: Provides load for diode, limits meter current COMPLETE DUAL-DETECTOR SCHEMATIC: FWD COUPLER OUTPUT │ ─┴─ C1 (100pF) ─┬─ │ │ ┌─┐ ├────┤ │ D1 (HP2835) │ └─┘ │ │ ─┴─ │ ─┬─ C2│ (100nF) │ │ GND ┌┴┐ R1 (10kΩ) │ │ └┬┘ │ ───→ FWD_DC │ (to meter driver) GND REF COUPLER OUTPUT │ ─┴─ C3 (100pF) ─┬─ │ │ ┌─┐ ├────┤ │ D2 (HP2835, matched to D1) │ └─┘ │ │ ─┴─ │ ─┬─ C4│ (100nF) │ │ GND ┌┴┐ R2 (10kΩ) │ │ └┬┘ │ ───→ REF_DC │ (to meter driver) GND DETECTOR RESPONSE: For square-law detection (low RF power): V_DC ≈ k × P_RF Where: k = detector constant (V/W) P_RF = RF power (W) For linear detection (high RF power): V_DC ≈ m × √P_RF Where: m = detector constant (V/√W) Transition occurs around -20 to -10 dBm RF power. For this SWR meter with -30 dB coupling: 100W main → 100mW (20 dBm) coupled This is in the transition/linear region Calibration accounts for detector non-linearity. IMPROVED DETECTOR (Compensated): For better low-power sensitivity, add bias compensation: From Coupler │ ─┴─ C1 (100pF) ─┬─ │ ┌────────────────────┴────────────┐ │ │ │ D1 (Forward biased) │ │ ┌─┐ │ ├────┤ │ HP2835 │ │ └─┘ │ │ │ │ │ ─┴─ C2 (100nF) │ │ ─┬─ │ │ │ │ ┌┴┐ │ ┌┴┐ R3 │ │ ┌┴┐ R1 (10kΩ) R4 │ │ 100kΩ│ │ │ 100kΩ│ └┬┘ └┬┘ └┬┘ │ │ │ │ ───→ FWD_DC │ │ │ │ └────┴─────────────────────────────┘ │ GND The bias resistors (R3, R4) provide a small forward bias current, reducing the diode's dead zone and improving low-level detection. Optional: Typically not needed for 5-200W power range. SECTION 5: METER DRIVER CIRCUITS ================================================================================ The meter driver circuits scale the DC detector outputs and drive the analog panel meters. BASIC METER DRIVER: From Detector To Meter (FWD_DC or REF_DC) │ │ ┌┴┐ R1 (Calibration pot, 10kΩ) │ │ │ │ ┌────────────────┐ └┬┘ │ │ ├─────┤ ├───→ Meter (100μA) │ │ │ ┌┴┐ R2 │ Range │ │ │ (Series resistance)│ │ │ │ │ └┬┘ │ │ │ └────────────────┘ │ GND METER SPECIFICATIONS: Typical analog panel meter: - Full-scale current: 100 μA - Internal resistance: 1-2 kΩ - Voltage for full-scale: 0.1-0.2V (V = I × R) DUAL-METER CONFIGURATION: FWD_DC REF_DC │ │ │ │ ┌┴┐ VR1 ┌┴┐ VR2 10kΩ│ │ CAL 10kΩ│ │ CAL │ │ │ │ └┬┘ └┬┘ ├──────────┐ ├──────────┐ │ │ │ │ ┌┴┐ R1 ┌┴┐ ┌┴┐ R3 ┌┴┐ │ │ │ │ M1 │ │ │ │ M2 4.7kΩ│ 100μA│ FWD 4.7kΩ│ 100μA│ REF │ │ │ │ │ │ │ │ └┬┘ └┬┘ └┬┘ └┬┘ │ │ │ │ GND GND GND GND VR1, VR2: Calibration potentiometers (trim pots) R1, R3: Series resistors to set meter full-scale M1, M2: 100μA panel meters SINGLE-METER CONFIGURATION (with switch): FWD_DC REF_DC │ │ │ │ ┌┴┐ VR1 ┌┴┐ VR2 10kΩ│ │ 10kΩ│ │ │ │ │ │ └┬┘ └┬┘ │ │ └────┬──────────┬─────────┘ │ SPDT │ ┌┴┐ Switch ┌┴┐ └┬┘ └┬┘ │ Common │ └─────┬─────┘ │ ┌┴┐ R1 (4.7kΩ) │ │ └┬┘ ├──────────┐ │ │ │ ┌┴┐ │ 100μA│ Meter │ │ │ │ └┬┘ │ │ GND GND Switch positions: - Position 1: Display FWD power - Position 2: Display REF power - Optional 3rd position: Calculate and display SWR (requires additional circuit) CALCULATING SERIES RESISTANCE: For full-scale meter deflection at maximum power: Example: 100W full scale, -30 dB coupling, HP2835 detector Coupled power: 100W × 0.001 = 0.1W = 100mW Detector output: ~2-3V DC (depends on diode, load) Meter needs: 100μA at 0.1V (typical 100μA meter with 1kΩ internal R) Voltage divider: R_series = (V_detector - V_meter) / I_meter Assuming V_detector = 2.5V at 100W: R_series = (2.5V - 0.1V) / 100μA = 2.4V / 0.0001A = 24,000Ω = 24kΩ Use 22kΩ fixed + 10kΩ pot for calibration. RANGE SWITCHING: For multiple power ranges (5W, 20W, 200W), switch in different resistors: From Detector To Meter │ │ ┌──────┐ ├─────────┤ ├── Position 1: R_200W (for 200W range) │ │ │ ├─────────┤Range ├── Position 2: R_20W (for 20W range) │ │Switch│ ├─────────┤ ├── Position 3: R_5W (for 5W range) │ │ │ GND └──────┘ │ ▼ Meter Example values (will require calibration): - R_200W = 22kΩ (200W full scale) - R_20W = 8.2kΩ (20W full scale, 10× more sensitive) - R_5W = 3.3kΩ (5W full scale, 40× more sensitive) Adjust during calibration for accurate readings. METER PROTECTION: Add diode to prevent reverse voltage (if meter disconnected): From Driver │ │ ┌┴────┐ │ │ │ ─┤├─ D1 (1N4148) │ ─┤├─ ┌┴┐ │ │ │ │ Meter│ │ │ │ │ └┬┘ │ │ │ └─────┘ │ GND D1 clamps any reverse voltage to ~0.7V, protecting meter. SECTION 6: RANGE SWITCHING ================================================================================ Range switching allows the meter to display different power levels accurately. THREE-RANGE DESIGN: Range 1: 5W full scale (QRP, antenna tuning) Range 2: 20W full scale (typical portable ops) Range 3: 200W full scale (high power ops) ROTARY SWITCH IMPLEMENTATION: Detector Output │ ┌────────────────┼────────────────┐ │ │ │ Position 1 Position 2 Position 3 (200W) (20W) (5W) │ │ │ ┌┴┐ ┌┴┐ ┌┴┐ R1 │ │ R2 │ │ R3 │ │ 22kΩ│ 8.2kΩ│ 3.3kΩ│ │ │ │ │ │ │ └┬┘ └┬┘ └┬┘ │ │ │ └────────────────┴────────────────┘ │ ┌┴┐ 100μA│ Meter │ │ └┬┘ │ GND FRONT PANEL SELECTOR: Rotary switch: 1-pole, 3-position Label positions: - 200W (or HIGH) - 20W (or MED) - 5W (or LOW) Operation: 1. Estimate transmitter power 2. Select appropriate range 3. Key transmitter briefly 4. Read meter 5. Switch to more sensitive range if needed (meter reads low) AUTOMATIC RANGE SWITCHING (Optional Enhancement): For automatic range selection, use comparators and analog switches: Detector Output │ ├───────┐ │ │ ┌┴┐ ┌┴────────────┐ │ │ │ Comparators │ R1 │ │ │ (LM339) │ │ │ │ │ └┬┘ └┬────────────┘ │ │ Control signals │ ▼ │ ┌──────────┐ ├──┤ Analog │ │ │ Switches │ │ │ (CD4066) │ │ └──────────┘ │ │ GND ▼ Meter Comparators detect signal level and automatically select appropriate range. Requires 9V battery but very convenient! This is an advanced modification - see manual Part 11 for details. SECTION 7: SECTION SELECTION (HF/VHF) ================================================================================ A selector switch routes signals through either HF or VHF/UHF coupler. SWITCH CONFIGURATION (DPDT Toggle): DPDT Switch INPUT ──────┬─────────┬───────── Position 1: HF Coupler │ │ │ ┌┴┐ │ └┬┘ │ │ │ ├────────── HF Coupler Input │ │ │ ┌┴┐ │ └┬┘ │ │ │ ├────────── VHF Coupler Input │ │ │ │ GND ─┴─ Position 2: VHF Coupler Similar switching for OUTPUT side. DETAILED WIRING: HF/VHF Toggle Switch (DPDT): Pole 1 (Input routing): - Common: From INPUT connector - Position 1: To HF coupler input - Position 2: To VHF coupler input Pole 2 (Output routing): - Common: To OUTPUT connector - Position 1: From HF coupler output - Position 2: From VHF coupler output Detection outputs (FWD_DC and REF_DC) from both couplers can be paralleled - only the selected coupler is active, so no conflict. FRONT PANEL INDICATOR: Label toggle positions: - HF (160M-10M) - VHF (6M-20CM) Optional: Add LED indicators showing which section is active. SIGNAL FLOW: HF Mode: INPUT → Switch → HF Coupler → Switch → OUTPUT │ ├→ FWD sample → Detector → Meter └→ REF sample → Detector → Meter VHF Mode: INPUT → Switch → VHF Coupler → Switch → OUTPUT │ ├→ FWD sample → Detector → Meter └→ REF sample → Detector → Meter SECTION 8: COMPLETE PARTS LIST ================================================================================ HF DIRECTIONAL COUPLER: ITEM QTY SPECS EST. COST ───────────────────────────────────────────────────────────────────────── RG-58 coax (main line) 1 50Ω, 200mm length $2-4 Twisted pair (coupled) 2 24 AWG, 200mm each $1-2 DC blocking caps 4 100pF, 50V, ceramic $1-2 Termination resistors 2 50Ω, 1/4W, 5% $0.50 SO-239 connectors 2 Panel mount $4-8 VHF/UHF DIRECTIONAL COUPLER: PCB (FR4, 1.6mm) 1 80×50mm, order or DIY $10-20 SMD resistors (50Ω term) 2 0805, 1% $0.50 DC blocking caps 4 100pF, 0805 $1 Bypass caps 4 100nF, 0805 $0.50 SMA or SO-239 connectors 2 Edge mount $3-6 DETECTOR CIRCUITS: Schottky diodes 4 HP2835 or 1N5711 $2-4 DC blocking caps 4 100pF, ceramic $1 Filter caps 4 100nF, ceramic $1 Load resistors 4 10kΩ, 1/4W $0.50 METER DRIVERS: Calibration pots (trim) 2 10kΩ, multi-turn $2-4 Series resistors 6 Various values $1-2 Range switch 1 1P3T rotary, 3-position $5-10 METERS: Analog panel meters 2 100μA, 50-60mm face $15-30 or single meter 1 100μA (+ FWD/REF switch) $8-15 Meter protection diodes 2 1N4148 $0.50 SWITCHES AND CONTROLS: HF/VHF selector (DPDT) 1 Toggle, 3A rating $3-8 Range selector 1 Rotary, 1P3T $5-10 FWD/REF switch (optional) 1 SPDT toggle (if 1 meter) $2-5 HARDWARE AND WIRING: Project wire - 22-24 AWG, various $3-5 Hardware (screws, nuts) - M3, stainless $3-5 Standoffs - 10mm, M3 $2-4 ENCLOSURE: 3D printing filament - PETG, ~200g $8-12 or aluminum enclosure 1 180×120×60mm $25-40 TOTAL COST ESTIMATE: ──────────────────── Budget build (single meter, surplus): $60-90 Standard build (dual meter, new parts): $100-150 Premium build (high-quality meters, PCB): $120-180 SECTION 9: PCB LAYOUT GUIDELINES ================================================================================ For best performance, especially at VHF/UHF, proper PCB layout is critical. GENERAL PRINCIPLES: 1. GROUND PLANE: - Solid copper on bottom layer (no breaks) - Top layer: ground pour where possible - Multiple vias connecting top and bottom grounds 2. SHORT TRACES: - Detector circuits: keep all connections <10mm - RF traces: 50Ω controlled impedance - No sharp corners (use 45° or rounded) 3. COMPONENT PLACEMENT: - Group functional blocks - Detectors near couplers - Meter drivers near meters - Minimize trace lengths 4. SHIELDING: - Separate HF and VHF sections if on same PCB - Ground plane strips between sections - Consider separate PCBs for HF and VHF PCB STACK-UP (VHF/UHF COUPLER): ┌─────────────────────────────────────────┐ │ Top Layer: Signal traces, SMD pads │ ├─────────────────────────────────────────┤ │ FR4 Dielectric: 1.6mm, εr = 4.5 │ ├─────────────────────────────────────────┤ │ Bottom Layer: Solid ground plane │ └─────────────────────────────────────────┘ TRACE WIDTH CALCULATION: For 50Ω microstrip on 1.6mm FR4: - Trace width (W) ≈ 3.0mm - Height above ground (H) = 1.6mm Use online calculator or AppCAD to verify. VIA PLACEMENT: Purpose: Connect top and bottom grounds Spacing: 5-10mm apart around perimeter Size: 0.5mm drill, 1.0mm pad Location: - Around coupler traces - At connector ground pads - Between sections COPPER POUR: Top layer: - Pour ground copper in unused areas - Leave clearance around signal traces (0.5mm) - Connect pours with vias Bottom layer: - Solid copper (100% fill) - No breaks except for mounting holes MECHANICAL DIMENSIONS: PCB size: 80mm × 50mm (fits in enclosure) Mounting holes: 3mm diameter, 4 corners Edge clearance: 3mm from board edge Component keepout: 2mm from mounting holes SECTION 10: CALIBRATION CIRCUITS ================================================================================ Accurate calibration is essential for precise SWR measurements. CALIBRATION PROCEDURE OVERVIEW: 1. Set range switch to desired power level (e.g., 20W) 2. Apply known RF power to INPUT 3. Terminate OUTPUT with 50Ω dummy load (SWR = 1:1) 4. Adjust FWD calibration pot until meter reads correct power 5. Place SHORT or OPEN on OUTPUT (SWR = ∞, all power reflected) 6. Adjust REF calibration pot until meters read equal 7. Verify at multiple power levels 8. Repeat for each range CALIBRATION CIRCUIT (per channel): From Detector │ │ ┌┴┐ VR1 (Coarse adjust, 10kΩ) │ │ │ │ └┬┘ ├─────────┬───────→ To Range Switch │ │ ┌┴┐ ┌┴┐ VR2 (Fine adjust, 1kΩ) R1 │ │ │ │ 4.7kΩ│ │ │ │ │ └┬┘ └┬┘ │ │ │ GND GND VR1: Multi-turn trim pot, sets overall gain VR2: Single-turn trim pot, fine adjustment CALIBRATION STANDARDS: Option 1: Calibrated Power Meter - Use known-good RF power meter - Measure actual transmitter output - Adjust SWR meter to match Option 2: Calibrated Transmitter - Use transmitter with accurate power control - Set to specific power levels (5W, 20W, etc.) - Adjust SWR meter to match indicated power Option 3: Resistive Dummy Load + Calculation - Use 50Ω dummy load - Measure transmitter current: I (amps) - Calculate power: P = I² × 50 - Adjust meter to match calculated power KNOWN SWR CALIBRATION: To calibrate REF channel: 1. SHORT CIRCUIT: - Place short across OUTPUT connector - All power reflected (SWR = ∞) - FWD and REF should read equal - Adjust REF cal pot to match FWD reading 2. OPEN CIRCUIT: - Leave OUTPUT unconnected - All power reflected (SWR = ∞) - FWD and REF should read equal - Verify REF reading matches FWD 3. 50Ω LOAD (Matched): - Connect dummy load to OUTPUT - No reflection (SWR = 1:1) - REF should read zero - If not zero, check coupler directivity METER SCALE CREATION: If using blank meter faces, create custom scales: FORWARD POWER SCALE: Markings for 200W range: 0, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200W Markings for 20W range: 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20W SWR SCALE (on FWD or combined meter): Based on the ratio FWD/REF: SWR = (1 + √(REF/FWD)) / (1 - √(REF/FWD)) Calculate SWR for various REF/FWD ratios: - REF/FWD = 0: SWR = 1.0 - REF/FWD = 0.01: SWR = 1.2 - REF/FWD = 0.04: SWR = 1.5 - REF/FWD = 0.11: SWR = 2.0 - REF/FWD = 0.25: SWR = 3.0 - REF/FWD = 1.0: SWR = ∞ Mark these points on meter face. CREATING METER FACE: 1. Remove existing meter face (carefully!) 2. Measure meter dimensions 3. Design scale in graphics software (Inkscape, Illustrator) 4. Print on cardstock or photo paper 5. Cut to size 6. Install behind meter glass 7. Reassemble meter Or use included meter_face.scad to generate SVG. SECTION 11: CONSTRUCTION NOTES ================================================================================ HF COUPLER CONSTRUCTION: Method 1: Twisted Pair on Coax 1. Cut RG-58 coax to 150mm 2. Install SO-239 connectors on ends 3. Prepare twisted pair (2 wires, 24 AWG) 4. Lay twisted pair along coax 5. Secure with cable ties or tape every 20-30mm 6. Maintain 2-3mm spacing from coax 7. Connect one end via 100pF cap to detector 8. Terminate other end with 50Ω to ground Repeat for second coupled line (REF channel). Method 2: Bifilar on Ferrite Rod 1. Wind two wires together (bifilar) on ferrite rod 2. 10-15 turns, evenly spaced 3. Keep main coax centered through rod 4. Connect windings as coupled lines 5. Better low-frequency response 6. Slightly more complex VHF/UHF COUPLER CONSTRUCTION: Order PCB: 1. Export Gerber files from PCB design 2. Upload to JLCPCB, OSH Park, or PCBWay 3. Order minimum quantity (usually 3 or 5 boards) 4. Wait 1-2 weeks for delivery 5. Inspect for defects Assemble PCB: 1. Solder SMD components first (resistors, caps) 2. Use hot air or reflow for best results 3. Or careful soldering iron work (0.5mm tip) 4. Install connectors last 5. Clean flux residue with isopropyl alcohol 6. Inspect solder joints under magnification DETECTOR ASSEMBLY: On PCB or perfboard: 1. Install diodes (note polarity!) - Cathode (banded end) toward output 2. Install capacitors (blocking and filter) 3. Install load resistors 4. Keep all leads short (<5mm) 5. Solder carefully (avoid heat damage to diodes) 6. Test with ohmmeter (diodes should show ~0.3V drop forward) METER INSTALLATION: 1. Mark meter positions on front panel 2. Cut square or round holes (depending on meter shape) 3. Test fit meters 4. Secure with mounting brackets or screws 5. Connect wires (observe polarity!) 6. Test meter with 1.5V battery (should deflect) FINAL ASSEMBLY TIPS: 1. Work methodically (one section at a time) 2. Test each section before moving on 3. Use star grounding (single ground point) 4. Keep wiring neat and direct 5. Label all connections 6. Take photos before closing enclosure (for future reference) 7. Calibrate carefully and patiently TESTING: Initial tests (before calibration): □ Ohmmeter: Check for shorts □ Low power (1-5W): Meter should deflect □ 50Ω load: REF should be much less than FWD □ Open/short: FWD and REF should be similar TROUBLESHOOTING: No meter deflection: - Check diode polarity - Check wiring to meter - Verify RF is reaching coupler - Test meter with battery (meter itself working?) FWD and REF read the same: - Poor coupler directivity - Incorrect coupled line connections - Missing or incorrect termination resistors - Check coupler construction Readings vary with frequency: - Normal to some extent - Large variation: check coupler length/coupling - May need separate calibration per band Meter "jumps" or erratic: - Insufficient filtering (add more capacitance) - RF getting into meter circuit - Check grounding HIGH POWER NOTES: This design is rated for 200W HF, 100W VHF/UHF. For higher power: - Use tighter coupling (-40 dB instead of -30 dB) - Or add attenuator pad after coupler - Check diode current rating (most Schottky good to 100mA) - Ensure main line coax rated for power PORTABLE OPERATION: For field use: ✓ Install in rugged enclosure ✓ Add rubber feet or carrying handle ✓ Use panel-mount connectors (not PCB-mount) ✓ Secure all internal components (won't shift) ✓ Consider protective cover for meter faces ✓ Waterproof if used outdoors (silicone sealing) MAINTENANCE: Regular: - Keep meters clean (dust can affect accuracy) - Check connector tightness - Verify calibration annually As needed: - Recalibrate if dropped or damaged - Replace diodes if damaged by overload - Clean switch contacts if range switching erratic This SWR meter, when properly built and calibrated, will provide years of reliable service! 73 and accurate measurements! Design: Claude Code - 2025 Location: /antennas/swr_meter/schematics/ ================================================================================ END OF SWR METER SCHEMATICS ================================================================================