================================================================================ COMPACT PORTABLE TRANSMATCH - 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 T-Network Schematic (160M-10M) Section 3: VHF/UHF L-Network Schematic (6M-20CM) Section 4: Optional SWR Meter Circuit Section 5: Component Specifications and Values Section 6: Roller Inductor Design Section 7: Switched Inductor Alternative Section 8: Wiring and Layout Guidelines Section 9: Complete Parts List Section 10: Tuning Procedures Section 11: Construction Notes SECTION 1: OVERVIEW AND BLOCK DIAGRAM ================================================================================ This transmatch uses a dual-section design: - HF section (160M-10M): Balanced T-network topology - VHF/UHF section (6M-20CM): Simplified L-network topology BLOCK DIAGRAM: ┌─────────────────────────────────────┐ Transmitter │ │ Antenna (50Ω) │ TRANSMATCH │ │ │ ├───────────┤ ┌──────────────────────────────┐ ├───────── │ │ │ HF SECTION (160M-10M) │ │ │ INPUT │ │ T-Network │ │ OUTPUT │ SO-239 │ │ C1 - L1 - C2 │ │ SO-239 │ │ └──────────────────────────────┘ │ │ │ │ │ │ ┌──────────────────────────────┐ │ │ │ │ VHF/UHF SECTION (6M-20CM) │ │ │ │ │ L-Network (switched) │ │ │ │ └──────────────────────────────┘ │ │ │ │ │ │ [Optional SWR Meter] │ ├───────────┤ ├───────── │ │ │ Section Selector Switch │ └─────────────────────────────────────┘ OPERATING PRINCIPLE: 1. Select HF or VHF/UHF section using front panel switch 2. Adjust variable components for minimum SWR 3. T-network (HF) provides wide impedance range (10-1000Ω → 50Ω) 4. L-network (VHF) provides moderate range (25-200Ω → 50Ω) SECTION 2: HF T-NETWORK SCHEMATIC (160M-10M) ================================================================================ TOPOLOGY: Balanced T-Network (Series-Shunt-Series) INPUT (Transmitter Side): INPUT C1 L1 C2 OUTPUT SO-239 (Variable) (Roller or (Variable) SO-239 (50Ω) 15-500pF Switched) 15-500pF (To Ant) │ 5-30μH │ │ ││ ││ │ ├─────────────────┤├────────────────╪╪─────────────┤├─────────────┤ │ ││ ║║ ││ │ │ ║║ │ │ ║║ │ GND ║║ GND ║║ ║║ L1 (Inductor) ║║ Tapped or Roller ║║ 5-30 μH range ║║ GND DETAILED T-NETWORK WITH ROLLER INDUCTOR: C1 (INPUT) C2 (OUTPUT) Variable Capacitor Variable Capacitor 15-500 pF 15-500 pF 500V minimum 500V minimum ││ ││ INPUT ├──────────────────┤├────┬───────────────────┬──────┤├───────┤ OUTPUT 50Ω ││ │ │ ││ To Ant │ │ ╔╧╗ ╔╧╗ ╠═╣ L1 ╚═╝ Optional ╠═╣ Roller Tap Point ╠═╣ Inductor (for matching) ╠═╣ 5-30 μH ╠═╣ 10A rating ╚═╝ │ GND COMPONENT FUNCTIONS: C1 (Input Capacitor): - Matches transmitter (50Ω) to series inductance - Adjustable 15-500 pF - Voltage rating: 500V minimum (1000V recommended for 100W) - Air dielectric variable capacitor - Knob on front panel: "INPUT TUNE" L1 (Series Inductor): - Provides reactance for impedance transformation - Roller inductor: 5-30 μH continuous adjustment - Current rating: 10A minimum - Can be tapped for additional matching options - Knob on front panel: "INDUCTANCE" or tap switch C2 (Output Capacitor): - Matches inductance to antenna impedance - Adjustable 15-500 pF - Same specs as C1 - Knob on front panel: "OUTPUT TUNE" TYPICAL COMPONENT VALUES BY BAND: Band Frequency C1 L1 C2 Notes ──────────────────────────────────────────────────────────────────────── 160M 1.8 MHz 250pF 30μH 300pF Full inductor range 80M 3.5 MHz 180pF 25μH 200pF High L needed 40M 7.0 MHz 120pF 18μH 150pF Mid-range L 30M 10.1 MHz 200pF 22μH 180pF WARC band 20M 14.0 MHz 80pF 12μH 100pF Popular DX band 17M 18.1 MHz 100pF 15μH 90pF WARC band 15M 21.0 MHz 70pF 10μH 80pF High band 12M 24.9 MHz 60pF 8μH 70pF WARC band 10M 28.0 MHz 50pF 5μH 60pF Minimum L Note: These are starting points. Actual values depend on antenna impedance. INDUCTOR TAP POINTS (Optional Enhancement): If using tapped inductor for additional matching flexibility: L1 (Tapped Coil) ╔═══════╗ ← Top (full inductance) ║ • ║ ← Tap 1 (80% of total) ║ • ║ ← Tap 2 (60% of total) ║ • ║ ← Tap 3 (40% of total) ║ • ║ ← Tap 4 (20% of total) ╚═══════╝ ← Bottom (GND) Tap selection via rotary switch provides coarse adjustment, C1/C2 provide fine adjustment. ALTERNATIVE: SWITCHED COIL CONFIGURATION Instead of roller inductor, use multiple fixed coils: Rotary Switch │ ┌──────────────────────┼────────────────────────┐ │ │ │ │ │ ╔╧╗ ╔╧╗ ╔╧╗ ╔╧╗ ╔╧╗ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ 30μH ║ ║ 20μH ║ ║ 12μH ║ ║ 8μH ║ ║ 5μH ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ╚╧╝ ╚╧╝ ╚╧╝ ╚╧╝ ╚╧╝ │ │ │ │ │ GND GND GND GND GND Less expensive than roller inductor, but step tuning vs. continuous. SECTION 3: VHF/UHF L-NETWORK SCHEMATIC (6M-20CM) ================================================================================ TOPOLOGY: Switchable L-Network For VHF/UHF bands, a simpler L-network provides adequate matching with lower component losses than a T-network. BASIC L-NETWORK (High-Pass Configuration): INPUT L1 OUTPUT 50Ω (Series) To Ant │ ┌─┐ │ ├──────────────────────┤ ├────────────────────────────┤ │ └─┘ │ │ │ │ C1 │ │ ││ │ │ ┤├ (Shunt) │ │ ││ │ GND │ GND GND BAND-SWITCHED VHF/UHF NETWORK: Band Select Switch (6M/2M/1.25M/70cm/33cm/20cm) │ ┌────────────────┼───────────────┐ │ │ │ INPUT ├─────┴────────────────┴───────────────┴──────┤ OUTPUT │ │ │ ╔════════════════════════════╗ │ │ ║ Switched Inductors (L1) ║ │ │ ║ ║ │ │ ║ 6M: 80 nH ║ │ │ ║ 2M: 30 nH ║ │ │ ║ 1.25M: 20 nH ║ │ │ ║ 70cm: 10 nH ║ │ │ ║ 33cm: 5 nH ║ │ │ ║ 20cm: 3 nH ║ │ │ ╚════════════════════════════╝ │ │ │ │ │ ╔════════════════════════════╗ │ │ ║ Switched Capacitors (C1) ║ │ │ ║ ║ │ │ ║ 6M: 50 pF ║ │ │ ║ 2M: 18 pF ║ │ │ ║ 1.25M: 12 pF ║ │ │ ║ 70cm: 6 pF ║ │ │ ║ 33cm: 3 pF ║ │ │ ║ 20cm: 2 pF ║ │ │ ╚════════════════════════════╝ │ │ │ │ GND GND GND DETAILED BAND SWITCH IMPLEMENTATION: Using 2-pole 6-position rotary switch: POLE 1: Series Inductor Selection Common to Input ──┬─── Position 1: L1a (80nH) for 6M ├─── Position 2: L1b (30nH) for 2M ├─── Position 3: L1c (20nH) for 1.25M ├─── Position 4: L1d (10nH) for 70cm ├─── Position 5: L1e (5nH) for 33cm └─── Position 6: L1f (3nH) for 20cm POLE 2: Shunt Capacitor Selection Common to GND ────┬─── Position 1: C1a (50pF) for 6M ├─── Position 2: C1b (18pF) for 2M ├─── Position 3: C1c (12pF) for 1.25M ├─── Position 4: C1d (6pF) for 70cm ├─── Position 5: C1e (3pF) for 33cm └─── Position 6: C1f (2pF) for 20cm COMPONENT CONSTRUCTION (VHF/UHF): Inductors (Small Air-Wound Coils): - 6M (80 nH): 6 turns, 8mm ID, 10mm length, 18 AWG wire - 2M (30 nH): 3 turns, 6mm ID, 6mm length, 18 AWG wire - 1.25M (20 nH): 2 turns, 6mm ID, 4mm length, 18 AWG wire - 70cm (10 nH): 1.5 turns, 5mm ID, 18 AWG wire - 33cm (5 nH): 1 turn, 5mm ID, 18 AWG wire - 20cm (3 nH): 0.5 turn (semicircle), 5mm ID, 18 AWG Capacitors (Mica or NPO Ceramic): - Use silver-mica or COG/NPO ceramic capacitors - Voltage rating: 250V minimum - Temperature coefficient: NPO (±30 ppm/°C) - Lead inductance must be minimized (short leads!) VHF/UHF MATCHING RANGE: This L-network can match: - Impedances: 25Ω to 200Ω (to 50Ω) - SWR: Up to 4:1 can typically be reduced to <1.5:1 - Best performance: SWR < 3:1 input For higher SWR, use external antenna tuner or adjust antenna. SECTION 4: OPTIONAL SWR METER CIRCUIT ================================================================================ A built-in SWR meter can be added to monitor matching quality. CIRCUIT: Directional Coupler + Detector DIRECTIONAL COUPLER (Transmission Line Section) INPUT ├────────────────────╪═════════╪────────────────────┤ OUTPUT ║ Main ║ ║ Line ║ ┌──╫─────────╫──┐ │ ║ Coupled ║ │ FWD ║ Line ║ REV │ ╚═════════╝ │ ─┴─ ─┴─ ─┬─ D1 ─┬─ D2 │ │ ├─────┐ ├─────┐ ─┴─ │ ─┴─ │ ─┬─ C1 │ ─┬─ C2 │ │ │ │ │ GND ┌┴┐ GND ┌┴┐ │ │ R1 │ │ R2 │ │ │ │ └┬┘ └┬┘ FWD │ REV │ Meter │ Meter │ ↓ │ ↓ │ M1 GND M2 GND COMPONENT VALUES: D1, D2: 1N4148 or 1N5711 Schottky diodes C1, C2: 100 nF (0.1 μF) ceramic R1, R2: 10 kΩ M1, M2: 100 μA panel meters (optional) DIRECTIONAL COUPLER CONSTRUCTION: For HF (160M-10M): - Use parallel transmission line (twisted pair or PCB stripline) - Coupling: -20 to -30 dB - Main line: 50Ω coax (RG-58, RG-8X) - Coupled line: 4-6 inches parallel to main line - Spacing: 0.5-1.0 mm for -25 dB coupling PCB Layout (Stripline Coupler): Main Line: ════════════════════════════ 50Ω trace ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ Coupled trace Coupled Line: ──────────────────────────── (parallel) Ground Plane: ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ Bottom layer SIMPLIFIED SWR INDICATOR (LED-based): For portable use, two LEDs can indicate relative SWR: FWD REV LED LED │ │ ┌┴┐ ┌┴┐ ─────┤ ├───── ─────┤ ├───── From Detector └┬┘ └┬┘ │ │ GND GND - FWD bright, REV dim/off: Good match (SWR < 1.5:1) - Both similar brightness: Poor match (SWR > 2:1) - REV brighter than FWD: Very poor match or reversed connection PANEL METERS (Analog): If using analog meters: - M1 (Forward Power): 0-100W scale - M2 (Reflected Power): 0-100W scale - Calculate SWR: SWR = (1 + √(Pr/Pf)) / (1 - √(Pr/Pf)) Where: Pf = Forward power Pr = Reflected power SECTION 5: COMPONENT SPECIFICATIONS AND VALUES ================================================================================ HF SECTION COMPONENTS: C1, C2 (Variable Capacitors): ──────────────────────────── Type: Air dielectric variable capacitor Capacitance: 15-500 pF (or dual-gang 2×250 pF) Voltage: 500V minimum (1000V recommended for safety margin) Plates: Brass or silver-plated brass Shaft: 1/4" (6.35mm) diameter Mounting: Front panel mount Source: Surplus, new, or vacuum variable Cost: $15-100 each (depending on source and quality) Recommended Models: - Surplus: Hammarlund, Johnson, Cardwell (eBay, Fair Radio) - New: Antique Electronic Supply (#C-V365-250 dual gang) - Vacuum: Comet/Jennings CVDD-500-2-5S (expensive but excellent) L1 (Roller Inductor): ───────────────────── Type: Roller inductor or tapped coil Inductance: 5-30 μH continuous (or switched) Current: 10A minimum Wire: 12-14 AWG bare copper Former: Air-wound or low-loss plastic Turns: ~30-40 turns on 2" (50mm) former Pitch: 8-10 turns per inch Cost: $80-200 commercial, $15-30 DIY Commercial Sources: - Palstar RIU.5 (5-30 μH, perfect for this) - MFJ Enterprises (various models) - Barker & Williamson (vintage, eBay) DIY Construction (see Section 6): - 1/4" copper tubing, self-supporting - 3D printed former with grooves - Much cheaper, very satisfying! SO-239 Connectors: ────────────────── Quantity: 2 (input and output) Type: UHF chassis mount (SO-239) Mounting: Rear panel, 16mm holes Mates with: PL-259 coax connectors Cost: $2-5 each Hardware: ───────── Bus wire: 12 AWG tinned copper (50 cm) Shaft couplers: For potentiometers/knobs (3x) Mounting: Standoffs, screws, nuts (stainless) Cost: $10-15 total VHF/UHF SECTION COMPONENTS: L1a-f (Series Inductors): ───────────────────────── Type: Air-wound coils, silver-plated wire Wire: 18 AWG solid, silver-plated copper Former: 3-8mm plastic or air-wound Values: See Section 3 for winding specs Cost: $5-10 total (wire + forms) C1a-f (Shunt Capacitors): ───────────────────────── Type: Silver mica or NPO/COG ceramic Voltage: 250V minimum Tolerance: ±5% or better Temp Coeff: NPO (±30 ppm/°C) Values: 2pF, 3pF, 6pF, 12pF, 18pF, 50pF Lead length: Keep SHORT (<5mm) for low inductance Cost: $0.50-2.00 each ($8 total) Rotary Switch: ────────────── Type: 2-pole, 6-position rotary switch Contact: Make-before-break preferred Current: 3A minimum Mounting: Front panel Shaft: 1/4" diameter Cost: $5-15 Common Models: - CK Components C3D0206N-A - Electroswitch Series 24 - Alps SRBP series SECTION SELECTOR SWITCH: DPDT Toggle: ──────────── Type: DPDT (double-pole, double-throw) toggle Rating: 3A at 125VAC minimum Mounting: Front panel Function: Selects HF or VHF/UHF section Cost: $3-8 Wiring: Common 1 → INPUT from transmitter Common 2 → OUTPUT to antenna Position 1 (HF): Routes through T-network Position 2 (VHF): Routes through L-network SECTION 6: ROLLER INDUCTOR DESIGN ================================================================================ COMMERCIAL ROLLER INDUCTOR: Most straightforward option but expensive ($80-200). DIY ROLLER INDUCTOR: Much cheaper ($15-30) and excellent performance. DESIGN PARAMETERS: Former diameter: 2.0 inches (50 mm) Former length: 6 inches (150 mm) Wire: 14 AWG bare copper wire Turns: 40 turns Pitch: 8 turns per inch (3.2 turns per cm) Inductance range: 0-30 μH (continuous) Current rating: 15A Cost: $15-30 (DIY) CONSTRUCTION METHOD 1: Self-Supporting Coil Materials: - 14 AWG bare copper wire (20 feet) - Temporary winding form (2" PVC pipe) - Roller contact (brass or beryllium copper) - Mounting hardware Steps: 1. Wind wire on temporary PVC form 2. Space turns evenly (8 TPI) 3. Remove from form (coil is self-supporting) 4. Mount coil vertically 5. Add roller contact mechanism 6. Connect bottom to GND, top to C2 CONSTRUCTION METHOD 2: Grooved Former Materials: - 3D printed cylindrical former (50mm OD) - Spiral groove (pitch: 3.2 turns/cm) - 14 AWG bare copper wire - Roller contact assembly Advantages: - More stable turn spacing - Easier to wind - Groove guides wire placement 3D Printed Former (OpenSCAD): module roller_coil_former() { difference() { // Main cylinder cylinder(d=50, h=150, $fn=100); // Center hole for mounting rod cylinder(d=6, h=160, center=true, $fn=50); // Spiral groove for wire for (i = [0:1:40]) { translate([0, 0, i * 3.75]) // 3.75mm pitch rotate([0, 0, i * 360/8]) // Spiral rotate([90, 0, 0]) translate([27, 0, 0]) cylinder(d=4, h=60, center=true, $fn=20); } } } ROLLER CONTACT MECHANISM: Shaft (attached to knob) │ ▼ ┌────┴────┐ │ Roller │ ← Brass or BeCu contact │ Ball │ Spring-loaded └────┬────┘ │ ═════════╪═════════ ← Coil winding ═════════╧═════════ (contact point) The roller moves up/down the coil, selecting inductance: - Bottom position: Minimum inductance (~0.5 μH) - Mid position: Mid-range (~15 μH) - Top position: Maximum inductance (~30 μH) ALTERNATIVE: Sliding Contact Instead of roller, use a sliding phosphor bronze contact: Slider ║ ║ Contact wire ═══════╬═══════ ← Coil ═══════╬═══════ ║ Simpler but more friction. Works well if coil is firmly mounted. INDUCTANCE CALCULATION: For air-core solenoid: L (μH) = (d² × n²) / (18d + 40l) Where: d = coil diameter (inches) n = number of turns l = coil length (inches) Example (this design): d = 2.0 inches n = 40 turns l = 5.0 inches L = (2² × 40²) / (18×2 + 40×5) L = 6400 / (36 + 200) L = 6400 / 236 L ≈ 27 μH Close to our 30 μH target. Adjust turns as needed. SECTION 7: SWITCHED INDUCTOR ALTERNATIVE ================================================================================ If roller inductor is too complex or expensive, use switched fixed coils. CONCEPT: Multiple fixed inductors selected by rotary switch Advantages: ✓ Less expensive ($20-40 vs. $80-200) ✓ Easier to construct ✓ No moving contacts to wear ✓ Can use air-wound coils ✓ Excellent Q factor Disadvantages: ✗ Step tuning (not continuous) ✗ May need more adjustment of C1/C2 ✗ More components RECOMMENDED INDUCTOR VALUES: Position Value Bands Construction ───────────────────────────────────────────────────────── 1 30 μH 160M, 80M 40T, 2" dia, 5" long 2 20 μH 80M, 40M 32T, 2" dia, 4" long 3 12 μH 40M, 30M, 20M 26T, 2" dia, 3" long 4 8 μH 20M, 17M, 15M 21T, 2" dia, 2.5" long 5 5 μH 15M, 12M, 10M 17T, 2" dia, 2" long All coils: 14 AWG bare copper, air-wound or on low-loss former ROTARY SWITCH WIRING: Rotary Switch (1-pole, 5-pos) │ ┌────────────────┼─────────────────┐ │ │ │ │ │ ╔╧╗ ╔╧╗ ╔╧╗ ╔╧╗ ╔╧╗ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ║30μH ║ ║20μH ║ ║12μH ║ ║8μH ║ ║5μH ║ ║ ║ ║ ║ ║ ║ ║ ║ ║ ╚╧╝ ╚╧╝ ╚╧╝ ╚╧╝ ╚╧╝ │ │ │ │ │ GND GND GND GND GND Switch Type: - 1-pole, 5-position rotary - Make-before-break (shorting type) - 5A current rating minimum - Front panel mount with scale Coil Construction: - Wind on 2" (50mm) diameter forms - Space turns evenly for maximum Q - Mount coils on ceramic standoffs - Keep leads short - Ground one end, switch other end ALTERNATIVE: Plug-in Coils For ultimate flexibility, make coils plug-in: [Coil 1] ──┐ ├──── Binding Posts ──── Circuit [Coil 2] ──┘ Advantages: - Easy to change coils - Can optimize each coil individually - Can build coils as needed - Easy to experiment Disadvantages: - Less convenient to use - More time to change bands - Possible contact issues SECTION 8: WIRING AND LAYOUT GUIDELINES ================================================================================ GENERAL PRINCIPLES: 1. SHORT RF PATHS - Keep all RF connections as short as possible - Minimize lead inductance - Direct point-to-point wiring 2. STAR GROUNDING - All grounds converge at single point - Prevents ground loops - Use chassis as ground plane 3. COMPONENT PLACEMENT - C1 near input connector - L1 in center - C2 near output connector - Linear signal flow 4. MECHANICAL STRENGTH - Secure all components firmly - Capacitors must not move under vibration - Support heavy components (inductor) PHYSICAL LAYOUT (Top View): ┌─────────────────────────────────────────────────────────┐ │ INPUT OUTPUT │ │ SO-239 C1 L1 C2 SO-239 │ │ │ ╱│╲ ╔═══╗ ╱│╲ │ │ │ ●─────( • )───────║ ║───────────( • )────────● │ │ ╲│╱ ║ ║ Roller ╲│╱ │ │ │ ║ ║ Inductor │ │ │ GND ╚═══╝ GND │ │ │ │ │ GND │ │ │ │ [VHF/UHF Section Below] │ │ │ │ HF/VHF Selector Switch Band Switch (VHF) │ │ (DPDT) (2P6T) │ └─────────────────────────────────────────────────────────┘ WIRING GUIDELINES: Bus Wire: - Use 12 AWG tinned copper bus wire - Keep runs straight and direct - Support with standoffs if needed - Solder all connections (no crimps at RF) Ground Connections: - Star ground: All GND converge at one point - Use chassis as ground plane (metal enclosure) - Or use copper tape/sheet (plastic enclosure) - Ground point near center of RF path Capacitor Mounting: - Securely mounted to front panel - Shaft through panel - Knob on outside - Leads kept short (< 2 inches) - Direct connection to RF path Inductor Mounting: - Vertical orientation (reduces footprint) - Mounted on ceramic/plastic standoffs - Away from metal surfaces (air core needs clearance) - At least 1" clearance from enclosure walls Interconnections: - Use bus wire for HF (not coax within enclosure) - Coax only for external connections - Avoid sharp bends in wire - Keep VHF and HF sections separated RF Connectors: - SO-239 rear panel mounted - Short, direct connection to circuit - Use star washers for good ground contact - Seal with silicone if outdoor use COMPONENT LEAD DRESS: Good Lead Dress (Low Inductance): Component ──┐ └── Direct, short connection │ GND Poor Lead Dress (High Inductance): Component ──┐ └──┐ │ Long loop └──┐ │ GND At VHF/UHF, even small lead inductance matters! SHIELDING (Optional but Recommended): For best performance, separate HF and VHF sections: ┌─────────────────┬─────────────────┐ │ HF Section │ VHF Section │ │ (T-Network) │ (L-Network) │ │ │ │ │ C1 - L1 - C2 │ Switch + L/C │ │ │ │ └─────────────────┴─────────────────┘ ▲ ▲ Shield divider (copper tape or metal) Prevents interaction between sections. SECTION 9: COMPLETE PARTS LIST ================================================================================ HF T-NETWORK SECTION: ITEM QTY SPECS EST. COST ───────────────────────────────────────────────────────────────────────── Variable capacitor (C1) 1 15-500pF, 500V min $15-50 Variable capacitor (C2) 1 15-500pF, 500V min $15-50 Roller inductor (L1) 1 5-30μH, 10A $80-200 OR: Switched inductors 5 5μH, 8μH, 12μH, 20μH, $20-40 30μH, air-wound Rotary switch (for coils) 1 1P5T, 5A $8-15 SO-239 connector (input) 1 UHF chassis mount $3-5 SO-239 connector (output) 1 UHF chassis mount $3-5 VHF/UHF L-NETWORK SECTION: Air-wound inductors 6 See Section 3 specs $5-10 Silver mica capacitors 6 2, 3, 6, 12, 18, 50pF $8-15 Rotary switch 1 2P6T make-before-break $10-18 DPDT toggle (HF/VHF) 1 3A, 125VAC $3-8 HARDWARE AND WIRING: Bus wire (12 AWG) 3ft Tinned copper $3-5 Shaft couplers 3 6.35mm (1/4") $6-12 Knobs 3-5 1/4" shaft, pointer style $9-20 Ceramic standoffs 4-8 For inductor mounting $5-10 Hardware (screws, nuts) - Stainless steel $5-10 Solder - 60/40 or lead-free $5-10 OPTIONAL SWR METER: Diodes (1N4148) 2 General purpose $0.50 Capacitors (100nF) 2 Ceramic $0.50 Resistors (10kΩ) 2 1/4W $0.20 Panel meters 2 100μA (FWD, REV) $20-40 OR: LEDs 2 Green (FWD), Red (REV) $1-2 ENCLOSURE (if not 3D printing): Aluminum enclosure 1 200×150×80mm $30-60 OR: 3D printing filament - PETG, ~250g $8-12 WIRE AND COAX: Magnet wire (for coils) 100ft 14 AWG, enamel $10-15 Coax jumpers (internal) 2ft RG-316 or RG-174 $5-8 TOTAL COST ESTIMATE: ──────────────────── Budget build (surplus caps, DIY inductor): $150-200 Standard build (new caps, commercial inductor): $250-350 Premium build (vacuum caps, high quality): $350-500 Add $50-100 if purchasing enclosure instead of 3D printing. SECTION 10: TUNING PROCEDURES ================================================================================ INITIAL SETUP: 1. SAFETY FIRST: - Use LOW POWER initially (5-10W maximum) - Connect dummy load or antenna - NEVER transmit without load! 2. CONNECT TEST EQUIPMENT: - External SWR meter between transmitter and tuner - Transmitter → SWR meter → Tuner → Dummy load - Set transmitter to CW or carrier mode 3. BAND SELECTION: - For HF: Select "HF" on section switch - Set frequency on transmitter - For VHF: Select "VHF" and choose band on rotary switch HF TUNING PROCEDURE (T-Network): Step 1: SET STARTING POSITIONS C1 (Input): 50% rotation (mid-range) L1 (Inductor): Match band (see Section 2 table) C2 (Output): 50% rotation (mid-range) Step 2: KEY TRANSMITTER (Low Power!) Observe SWR on meter Typical starting SWR: 3:1 to 10:1 (this is normal!) Step 3: ADJUST OUTPUT CAPACITOR (C2) Slowly rotate C2 knob Watch for SWR to DROP Find position of minimum SWR If SWR doesn't improve significantly: → Adjust L1 (inductor) and try again Step 4: ADJUST INPUT CAPACITOR (C1) Rotate C1 knob slowly SWR should drop further Find minimum SWR point Step 5: ITERATE Go back to C2, fine-tune Then back to C1 Repeat until SWR < 1.5:1 Step 6: VERIFY Target: SWR < 1.5:1 (excellent) SWR < 2.0:1 (acceptable) If cannot achieve <2:1, try different L1 setting QUICK TUNING METHOD (for experienced operators): 1. Adjust L1 until you hear "dip" in reflected power 2. Tweak C2 for deepest dip 3. Touch up C1 for final null 4. Total time: 10-30 seconds VHF/UHF TUNING PROCEDURE (L-Network): Step 1: SELECT BAND Rotate VHF band switch to desired band Example: 2M position for 2-meter band Step 2: KEY TRANSMITTER Use LOW power (5W or less initially) Observe SWR Step 3: VERIFY MATCH With proper band selection, SWR should be <2:1 If not, check: - Correct band selected? - Antenna impedance in range (25-200Ω)? - All connections secure? Note: VHF/UHF L-network has fixed values per band. Limited adjustment possible. If match is poor, antenna or external tuner adjustment needed. TUNING FOR DIFFERENT ANTENNAS: Random Wire / End-Fed: - Usually high impedance (200-1000Ω) - Requires high L1, high C2 - Can be very reactive (high SWR) - May need several adjustment cycles Dipole (slight mismatch): - Near 50Ω, small adjustment - Low L1 settings - Quick to tune Vertical with Radials: - Usually 35-75Ω depending on ground - Medium L1 settings - Relatively easy to match Multiband Antennas: - Impedance varies by band - Retune completely when changing bands - Keep tuning chart for each band TUNING CHART TEMPLATE: Create a chart for quick setup: Band Frequency C1 Setting L1 Setting C2 Setting SWR ───────────────────────────────────────────────────────────── 80M 3.750 MHz 60% 20 μH 70% 1.3:1 40M 7.100 MHz 40% 15 μH 45% 1.2:1 20M 14.100 MHz 30% 10 μH 35% 1.1:1 ... Record actual knob positions (degrees or % rotation) for your specific antenna system. Saves time when switching bands! SECTION 11: CONSTRUCTION NOTES ================================================================================ PCB vs. POINT-TO-POINT: This transmatch can be built using either method: POINT-TO-POINT (Recommended): ✓ Easier for beginners ✓ No PCB design/fabrication needed ✓ Easy to modify ✓ Short, direct RF paths ✓ Works excellently at HF frequencies Method: - Mount components on ceramic standoffs - Use bus wire for interconnections - Ground all components to common chassis point - Very robust construction PCB (Advanced): ✓ Neater appearance ✓ Reproducible (if making multiple units) ✓ Better for VHF/UHF (controlled impedances) Caution: - PCB design beyond scope of this document - Trace widths important (50Ω impedance) - Via placement critical for grounding - Consider using PCB for VHF section only COIL WINDING TIPS: 1. EVEN SPACING: - Use coil winding jig or lathe - Or: 3D print former with grooves - Consistent spacing = higher Q = better efficiency 2. WIRE PREPARATION: - Remove enamel from ends (scrape or burn) - Tin ends with solder for good connections - Don't kink wire (reduces current capacity) 3. SECURING TURNS: - Use small dabs of glue between turns - Or: drill small holes in former for wire ends - Ensure coil can't shift under vibration 4. TESTING INDUCTANCE: - Use LCR meter if available - Or: resonate with known capacitor - Formula: f = 1 / (2π√LC) CAPACITOR SELECTION GUIDE: Budget Option ($15-30 each): - Surplus air variable caps from eBay - Look for: Hammarlund, Johnson, Cardwell brands - Check voltage rating (500V minimum) - Test before installing (verify smooth rotation) Mid-Range ($40-70 each): - New air variable capacitors - Antique Electronic Supply - Variable capacitor suppliers Premium ($100+ each): - Vacuum variable capacitors - Excellent voltage handling (5-10 kV) - Compact size - Zero arcing risk - Best for high power (>100W) SAFETY - HIGH VOLTAGE: Even at 100W, capacitor plates can have HIGH VOLTAGE: Power Voltage (peak) ────────────────────── 100W 100-300V 200W 150-400V Dangers: ⚠ Capacitor plates can BITE! (painful shock) ⚠ Capacitors can STORE CHARGE (discharge before touching) ⚠ Sharp edges on plates (mechanical hazard) Safety measures: ✓ Keep enclosure CLOSED during operation ✓ Discharge caps before opening (short terminals with insulated tool) ✓ Use insulated knobs (don't touch capacitor body during TX) ✓ Never work on transmatch while transmitting WEATHERPROOFING: For outdoor/portable use: Enclosure: - PETG or ABS (better than PLA for outdoors) - Seal seams with silicone - Conformal coating on circuit boards Connectors: - Use rubber boots on coax connectors - Silicone sealant around panel penetrations - Keep connectors facing down (drip edge) Components: - Spray coils with acrylic conformal coating - Protect capacitor from rain (enclose) - Use stainless hardware (no rust) TESTING WITHOUT ANTENNA: DUMMY LOAD is essential for initial testing! Dummy Load = 50Ω resistor, appropriate wattage: - 100W: Use two 100Ω 50W resistors in parallel - 50W: Single 50Ω 50W resistor - QRP: 50Ω 5-10W resistor Why? - Safe testing without RF radiation - Known impedance (50Ω) - Protects transmitter during tuning experiments MODIFICATIONS: 1. ADD MORE INDUCTANCE TAPS More coil taps = finer adjustment 2. MOTORIZE TUNING Add stepper motors to C1, C2, L1 Remote tuning from operating position 3. ADD DIGITAL READOUT Display C1, C2, L1 positions Recall saved settings 4. HIGHER POWER Use larger capacitors (higher voltage) Larger inductor (heavier wire) Better cooling 5. ADD BALUN 4:1 or 6:1 balun for balanced antennas Mounts between tuner and antenna TROUBLESHOOTING: Problem: Cannot achieve SWR < 2:1 Solution: - Check all connections - Try different inductor settings - Verify antenna is connected - Check antenna impedance (may be out of range) Problem: Arcing in capacitor Solution: - Reduce power immediately - Capacitor voltage rating too low - Or: extreme mismatch (very high SWR) - Use higher voltage capacitor Problem: Poor efficiency (antenna doesn't radiate well) Solution: - Check ground system (critical!) - Verify inductor connections (all turns conducting) - Look for oxidized connections Problem: VHF/UHF section doesn't match Solution: - Check component values (correct pF, nH?) - Verify short leads on caps/inductors - Ensure good ground connections - Antenna impedance may be out of range (25-200Ω) Problem: Inductor gets hot Solution: - Normal: slight warmth - Hot to touch: reduce power or check current rating - Too much loss: check wire gauge, connections FINAL NOTES: This transmatch design provides excellent performance across all amateur bands from 160M through 20CM. The hybrid HF/VHF approach ensures optimal matching for the wide frequency range. Key Success Factors: ✓ Quality variable capacitors (don't skimp here!) ✓ Good ground system on antenna ✓ Short RF paths in construction ✓ Patient tuning procedure ✓ Start with LOW POWER for testing Build it, tune it carefully, and enjoy perfectly matched antennas on all bands! 73 and good DX! Design: Claude Code - 2025 Location: /antennas/transmatch/schematics/ ================================================================================ END OF TRANSMATCH SCHEMATICS ================================================================================