================================================================================ BALUN 4:1 CURRENT (GUANELLA) — TRANSMISSION-LINE TRANSFORMER ================================================================================ Purpose: Impedance transformation 200Ω balanced → 50Ω unbalanced (4:1) Common-mode suppression on matched balanced feedlines Type: Transmission-Line Transformer (TLT), current balun design CM Suppression: Excellent (ferrite-based, 20+ dB across HF) Insertion Loss: 0.15–0.25 dB (HF), <0.15 dB @ 10M ================================================================================ CIRCUIT DIAGRAM — GUANELLA 4:1 BALUN ================================================================================ ┌────────────────────────────┐ │ BALANCED ANTENNA FEED │ │ (200Ω dipole or window) │ └──────────┬─────────────────┘ │ ┌────────┴─────────┐ │ │ Leg A Leg B │ │ ┌──┴─────────┐ ┌───┴──────┐ │ #16 wire │ │ #16 wire │ │ wrapped in │ │ wrapped │ │ BIFILAR │ │ BIFILAR │ │ pair on │ │ on │ │ FT-140-43 │ │FT-140-43 │ │ core stack │ │ stacked │ └──┬─────────┘ └───┬──────┘ │ │ ├──────────┬───────┤ │ (Center) │ Coax │ ┌───────┴────────┐ │ 50Ω Receiver │ │ or TX Line │ └────────────────┘ Alternate (Series Configuration): ┌────────────────────────────┐ │ BALANCED INPUT (200Ω) │ └──────────┬─────────────────┘ │ ┌────────┴─────────┐ │ │ PRIMARY SECONDARY (TLT Stage 1) (TLT Stage 1) │ │ ┌──┴──┐ ┌──┴──┐ │ ZL │ │ ZL │ (Center-tapped output) └──┬──┘ └──┬──┘ │ │ └────────┬─────────┘ │ (Center tap) │ 50Ω OUT ================================================================================ CORE SPECIFICATIONS ================================================================================ HF Configuration (160M–10M): Cores: 2× FT-140-43 stacked Material: Mix 43 (µ=850, AL=520 µH/100T per core) Stacking: Series connection (AL_total ≈ 1040 µH/100T) Wire: #16 enameled copper Turns per core: 6–10 (depending on band) Max Power: 350 W (with adequate heatsinking) Winding Details (per core): 160M: 10 turns (bifilar pair) 80M: 9 turns 40M: 8 turns 30M: 7 turns 20M: 7 turns 17M: 6 turns 15M: 6 turns 10M: 6 turns Wire Length Estimate: Each core: ~80–120 inches (depending on turns) Total (2 cores): ~160–240 inches ================================================================================ IMPEDANCE TRANSFORMATION THEORY — GUANELLA TLT ================================================================================ The Guanella balun uses TRANSMISSION-LINE segments, not ideal transformer action. Key Property: Z_out = Z_c × (Z_in / Z_c)² [NOT Z_out = Z_in / N²] Instead, transformation comes from parallel-series connection: - Two transmission lines carrying differential signal - Each TL has characteristic impedance Z_c ≈ 200Ω - Series connection of two 200Ω TLs in parallel = 100Ω combined - For balanced 200Ω input, output impedance = 50Ω TURNS RATIO INTERPRETATION: 2:1 turns ratio ≠ direct impedance step (as in voltage balun) Instead, 2:1 ratio determines delay length of each TL stage Delay ≈ λ/4 @ design frequency (quarter-wave transformer operation) BIFILAR WINDING: Two wires wound together (twisted pair, not separate) Creates two TL segments with matched impedance Primary source of 1:1 common-mode suppression ================================================================================ WINDING TECHNIQUE — GUANELLA BIFILAR ================================================================================ Materials: - 2× FT-140-43 cores - 2× spools of #16 enameled copper - Small vice or holding jig - Wire stripper Step 1: Prepare wire pairs - Cut two equal lengths of #16 wire (~120 inches for full HF) - Strip ~0.5" from each end - Twist wires together loosely (uniform helix) - Tension to eliminate slack but not crimp jacket Step 2: Wind first core (primary) - Thread twisted pair through core hole - Wrap around core (8–10 passes = 8–10 turns bifilar) - Keep pair together (no separation) - Evenly distribute around circumference Step 3: Wind second core (secondary) - Continue same twisted pair onto second core - Stack second core adjacent to first (aligned axially) - Same turns as first core - Maintain even spacing Step 4: Make connections - Primary input: Solder one end of twisted pair to antenna leg A - Second antenna leg: Solder to wire at core-to-core junction (center tap) - Secondary output: Solder remaining end to coax center conductor - Coax braid: Connect to center-tap point (RF ground) Step 5: Insulation and weatherproofing - Ensure enamel on wire is not damaged during winding - Optional: Wrap entire assembly with electrical tape - Potting compound (silicone) recommended for field units ================================================================================ COMMON-MODE OPERATION ================================================================================ Differential-Mode (desired signal): Each wire of bifilar pair carries equal but opposite currents These currents cancel external magnetic field (balanced) Z_differential ≈ 100Ω (from 2×50Ω TL stages in series) Common-Mode (unwanted): Both wires carry SAME current (on antenna side) or (on coax braid) Ferrite core provides impedance: Z_CM = 2πfL Z_CM = 2π × f × (AL × N² / 10000) Example @ 80M (3.75 MHz), 9 turns, 2×FT-140-43: L = 1040 × 81 / 10000 = 8.4 µH Z_CM = 2π × 3.75×10⁶ × 8.4×10⁻⁶ ≈ 198 Ω Attenuation ratio: A_CM = Z_CM / Z_0 ≈ 198 / 50 ≈ 4× (≈ 12 dB) ================================================================================ FREQUENCY RESPONSE ================================================================================ FT-140-43 stacked, 8 turns per core, typical HF response: Frequency Impedance Ratio CM Impedance Insertion Loss 1.8 MHz 4.1:1 ~160 Ω 0.25 dB 3.75 MHz 3.9:1 ~200 Ω 0.20 dB 7.15 MHz 3.8:1 ~350 Ω 0.18 dB 14.2 MHz 3.7:1 ~620 Ω 0.15 dB 28.4 MHz 3.6:1 ~980 Ω 0.12 dB Design Notes: - Impedance ratio stays flat ~3.6–4.1:1 across entire HF band ✓ - CM impedance RISES with frequency (inductive slope) - Insertion loss DECREASES with frequency (ferrite loss drops) ================================================================================ DESIGN EQUATIONS ================================================================================ Turns per core (for given band and impedance ratio): N = sqrt(Z_in × Z_out) / (2π × f × AL/10000) Example: 160M (1.8 MHz), FT-140-43 (AL=520), 200→50Ω (4:1): Z_characteristic ≈ sqrt(200 × 50) = 100Ω N_desired = ? In practice, use EMPIRICAL RULES from winding tables (provided separately) Insertion Loss (approximate): L_dB ≈ 0.1 + (0.01 × f_MHz) for FT-140-43 stacked Example @ 14.2 MHz: L ≈ 0.1 + 0.14 = 0.24 dB (reasonable match) Common-Mode Impedance: Z_CM = 2π × f × (AL × N²) / 10000 Target: Z_CM ≥ 250 Ω (5× rule applies to Guanella too) ================================================================================ PRIMARY APPLICATIONS ================================================================================ 1. BALANCED DIPOLES (200Ω feedpoint): - Window line (450Ω ladder line) requires 9:1 balun instead - 200Ω feedpoint (short dipole or T-dipole) → 4:1 Guanella - G5RV antenna @ impedance minima (200Ω points) 2. FOLDED DIPOLES: - Nominal impedance: 288–300Ω (some applications) - 4:1 Guanella suitable for matching 3. BALANCED MATCH WITH ANTENNA TUNER: - Tuner needs balanced input port (rare) - Guanella provides low-loss balanced 50Ω → 200Ω transformation - Allows tuner to see high-Z loads (>50Ω) 4. BROADBAND DIPOLE ARRAYS: - Multiple dipoles in series/parallel configurations - Guanella used to match combined impedance ================================================================================ TESTING PROCEDURE — NANOVNA ================================================================================ Setup: Port 1: Connect to coax output (50Ω) Port 2: Connect to one antenna leg (balanced input, use 50Ω adapter with 50Ω resistor to ground) OR: Use balun test fixture (50Ω source, 200Ω load, measure S-parameters) Measurement 1 — Insertion Loss (with 200Ω load): Sweep 1–30 MHz Expected: S₂₁ ≈ -0.15 to -0.25 dB S₁₁ ≈ -20 dB (good match when properly terminated) Measurement 2 — Common-Mode Impedance: With balanced input left floating (open): Measure S₁₁ of one leg to ground (should be highly reactive) Expected: Z ≈ j×Z_CM (inductive, rising with frequency) Measurement 3 — Phase matching: Measure phase difference between two legs @ balanced input Expected: 180° ± <5° (tight phase coherence) ================================================================================ FAILURE MODES & TROUBLESHOOTING ================================================================================ SYMPTOM: High SWR, antenna won't match ROOT CAUSE 1: Balun winding incorrect (turns count wrong) SOLUTION: Re-count turns, verify against winding table ROOT CAUSE 2: Bifilar pair separated during winding (lost transmission line action) SOLUTION: Unwind, re-twist wire pair, wind again ROOT CAUSE 3: Ferrite cores not stacked properly (misaligned) SOLUTION: Ensure cores are axially aligned, touching SYMPTOM: Excessive heating during transmission ROOT CAUSE: High common-mode current flowing (antenna imbalanced) SOLUTION: - Add counterpoise or ground plane (reduce CM) - Check for RF in shack (indicates high CM current) - Reduce power if heating severe ROOT CAUSE: Ferrite core saturated from excessive power SOLUTION: - Reduce TX power temporarily - Allow core to cool - Switch to larger core (FT-240-43 instead of FT-140) SYMPTOM: Pattern distortion (null in wrong direction) ROOT CAUSE: High CM current still flowing despite balun SOLUTION: - Verify balun impedance matches antenna load - Add ferrite choke on coax output (secondary CM suppression) - Check balun connections (verify center-tap grounded) ================================================================================ POWER HANDLING & THERMAL ================================================================================ Maximum Power (FT-140-43 stacked): Continuous (CW): 350 W @ 50°C ambient Peak (SSB): 500–700 W (transient) Thermal rise: ~30°C @ 500W input Thermal Management: - Ensure adequate airflow around cores - Monitor core temperature during high-power sessions - If core >60°C, reduce power or install on mast (ambient cooling) Cooling Strategies: - Mount on metal bracket (thermal sink) - Potting compound selection (silicone conducts heat better than epoxy) - Add aluminum fins (if extreme power required) ================================================================================ CONSTRUCTION NOTES ================================================================================ Mechanical Assembly: - Mount balun at antenna feedpoint (minimize feedline coupling) - Use stainless steel hardware (prevent corrosion) - Potting optional but recommended for weather protection Weatherproofing: - Silicone potting: Flexible, non-cracking, conducts heat moderately - Epoxy potting: Rigid, better mechanical strength, poor thermal conductivity - PVC electrical tape wrap: Quick field fix, moderate durability Field Repair: - Balun heating: Cut power, allow 10-minute cool period - Coax damage: Can re-solder connectors if internal conductors OK - Enamel damage on wire: Unlikely to affect operation unless shorted Spare Parts Kit: - 2× FT-140-43 cores (can stack to make stacked cores) - Spool of #16 enameled wire - N-connector and SO-239 plugs/jacks - Silicone potting compound ================================================================================ COMPARISON: GUANELLA vs VOLTAGE BALUN ================================================================================ Feature Guanella (Current) Voltage Balun ─────────────────────────────────────────────────────────── CM Suppression Excellent (ferrite in series) Fair (primary impedance) Bandwidth Broad (±50% from design freq) Moderate Insertion Loss 0.15–0.25 dB 0.1–0.15 dB Phase Match Very tight (<2° across band) Good (5°–10°) Power Handling Good (distributed current) Excellent (lower loss) Cost Moderate ($20) Low ($15) Field Repair Difficult (needs cores) Easy (simple winding) Recommendation: Use GUANELLA for balanced antennas requiring strong CM suppression Use VOLTAGE for simple impedance transformation where CM is low priority ================================================================================