================================================================================ BALUN 9:1 TRIFILAR — 450Ω LADDER LINE MATCHING ================================================================================ Purpose: Impedance transformation 450Ω balanced → 50Ω unbalanced Type: Trifilar current balun (three wires, same technique as 6:1) CM Suppression: Good (ferrite + trifilar symmetry) Insertion Loss: 0.25–0.40 dB (higher loss due to extreme impedance ratio) Primary Use: G5RV antennas, 450Ω ladder line, high-impedance feeds ================================================================================ CIRCUIT DIAGRAM — 9:1 TRIFILAR BALUN ================================================================================ ┌────────────────────────────┐ │ 450Ω BALANCED FEED │ │ (ladder line, G5RV style) │ └──────────┬─────────────────┘ │ ┌────────┴─────────┐ │ │ Leg A Leg B │ │ ┌──┴──────────┐ ┌─────┴─────┐ │ Trifilar │ │ Trifilar │ │ 4 turns │ │ 12 turns │ │ on FT-240-43│ │ (4:12 = │ │ core │ │ 1:3 ratio)│ │ (450Ω input)│ │(9:1 Z-tx) │ └──┬──────────┘ └─────┬─────┘ │ │ ├────────┬─────────┤ │ Coax │ ┌─────┴────┐ │ 50Ω Out │ │ (G5RV │ │ matcher)│ └──────────┘ ================================================================================ CORE SPECIFICATIONS ================================================================================ HF Configuration (160M–10M): Core: Single FT-240-43 (higher turns than 6:1 requires single core) Material: Mix 43 (µ=850, AL=1100 µH/100T) Wire: #14 enameled copper (thicker to handle higher turns) Turns: 4 primary, 12 secondary (exact 1:3 ratio) Impedance ratio: (1/3)² = 9:1 ✓ Max Power: 400 W (more core stress than 6:1) Insertion Loss: 0.30–0.40 dB (significant, acceptable for antenna tuning) Band-Specific Configuration: 160M (1.8 MHz): 4 primary, 12 secondary (FT-240-43×2 stacked recommended) 80M (3.75 MHz): 4 primary, 12 secondary (single FT-240-43) 40M (7.15 MHz): 4 primary, 11 secondary (compromise turn count) 30M (10.1 MHz): 3 primary, 9 secondary (reduced turns for impedance) 20M (14.2 MHz): 3 primary, 9 secondary (compact design) 10M (28.4 MHz): 3 primary, 9 secondary (upper HF limit) Wire Lengths: Primary: ~70 inches (4 turns, large core) Secondary: ~160 inches (12 turns) Total: ~230 inches per balun (longest of all HF baluns) ================================================================================ IMPEDANCE TRANSFORMATION THEORY — 9:1 ================================================================================ TURNS RATIO INTERPRETATION: N_ratio = 4:12 = 1:3 Z_ratio = N_ratio² = 3² = 9:1 ✓ VOLTAGE TRANSFORMATION: V_out / V_in = 1/3 ≈ 0.33 (large voltage step-down) V_in × I_in = V_out × I_out (power conservation) IMPEDANCE TRANSFORMATION: Z_out = Z_in / N² = 450 / 9 = 50Ω ✓ COMPARISON TO 6:1 AND 4:1: 4:1 matches 200Ω → 50Ω 6:1 matches 300Ω → 50Ω 9:1 matches 450Ω → 50Ω Each requires increasing turns ratio (and higher loss) ================================================================================ WINDING TECHNIQUE — 9:1 TRIFILAR ================================================================================ Nearly identical to 6:1, but with more turns (slightly more challenging). Materials: - 1× FT-240-43 core (FT-240-43×2 for 160M) - 3× spools of #14 enameled copper (thicker gauge) - Small vice and wire-guiding jig (compact form) Step 1: Prepare three wire strands - Cut three equal lengths (~230 inches each) - Stripe ends ~0.5" - Keep parallel (do NOT twist) Step 2: Wind three wires simultaneously - Hold all three strands parallel - Feed through core hole together - Wrap around core in synchronized pattern - Each pass = 3 turns (one per strand) - 4 passes = 4 turns per strand Step 3: Continue winding secondary - Without interruption, continue winding - 12 more passes on same core (strains core packing) - Total: 16 wire passes through core Step 4: Reconnect wires - Group wires 1+2: Primary (antenna input) - Solder to antenna feedpoint legs A and B - Wire 3 + center-tap: Secondary (50Ω output) - Solder wire 3 to coax center conductor Step 5: Weatherproofing - Potting STRONGLY recommended - 16 wire turns take up significant core space - Silicone potting protects from environmental damage - Heat dissipation important (higher loss than 4:1 or 6:1) Step 6: Assembly in enclosure - Mount on aluminum or ceramic base (thermal sink) - Ensure adequate ventilation - Optional: Heat-sink paste for potting contact ================================================================================ COMMON-MODE OPERATION ================================================================================ CM impedance calculation: Z_CM = 2π × f × L_total where L_total = AL × N_total² / 10000 Example @ 80M (3.75 MHz), FT-240-43, 4+12=16 total turns: L = 1100 × 256 / 10000 = 28.16 µH Z_CM = 2π × 3.75×10⁶ × 28.16×10⁻⁶ ≈ 665 Ω (good) Example @ 20M (14.2 MHz), FT-240-43, 3+9=12 total turns: L = 1100 × 144 / 10000 = 15.84 µH Z_CM = 2π × 14.2×10⁶ × 15.84×10⁻⁶ ≈ 1414 Ω (excellent) CM Suppression: Z_CM / Z₀ = 665 / 50 ≈ 13× (≈ 22 dB @ 80M) Rising to 28× (≈ 28 dB) @ higher frequencies RESULT: Excellent CM suppression, comparable to Guanella ================================================================================ FREQUENCY RESPONSE ================================================================================ FT-240-43, variable turns (optimized per band): Frequency Turns Z_in/Z_out Z_CM Loss 160M 4:12 450→50 665 Ω 0.40 dB 80M 4:12 450→50 730 Ω 0.30 dB 40M 4:11 450→48 690 Ω 0.25 dB 30M 3:9 450→50 580 Ω 0.22 dB 20M 3:9 450→50 520 Ω 0.20 dB 10M 3:9 450→50 480 Ω 0.18 dB Notes: - Impedance ratio stays flat ~450→50Ω across band ✓ - Loss higher than 4:1 or 6:1 (expected for extreme ratio) - Z_CM excellent across all bands (>250Ω minimum always met) ================================================================================ PRIMARY APPLICATIONS ================================================================================ 1. G5RV MULTIBAND ANTENNA: - Classic design with 102 feet of 450Ω ladder line feed - 9:1 balun converts ladder line to 50Ω coax - Operates 80M–10M (some reports even 160M with tuner) 2. 450Ω OPEN-WIRE FEEDLINES: - Commercial 450Ω window line or ladder line - Low-loss broadband feeds for dipoles 3. RANDOM WIRE MATCHING: - Some random wires exhibit ~450Ω feedpoint impedance - 9:1 unun preferred (voltage transformer, not balun) 4. BALANCED TUNER INTERFACE: - Antenna tuner with balanced ladder-line input - Tuner sees 450Ω load, outputs 50Ω coax 5. BROADBAND ANTENNA SYSTEMS: - Arrays of parallel dipoles (high combined impedance) - Multiple antennas in series-parallel configuration ================================================================================ TESTING PROCEDURE — NANOVNA ================================================================================ Setup: Port 1: Coax 50Ω output Port 2: Primary input (via 50Ω adapter, or direct with 450Ω load) Use test load: 450Ω resistor across primary Measurement 1 — Impedance Ratio: Sweep 1–30 MHz with 450Ω load on primary Expected: S₁₁ <-20 dB (excellent match) Z_in ≈ 450Ω (verify with resistive load) Measurement 2 — Insertion Loss: Sweep with 450Ω load connected Expected: S₂₁ ≈ -0.20 to -0.40 dB (higher loss than 4:1) Accept losses at low end of band (normal for HF) Measurement 3 — Phase balance: Measure phase delay through balun @ several frequencies Expected: <30° variation (indicates stable transformation) Measurement 4 — Common-Mode Impedance: With primary floating (open), measure impedance to ground Expected: Z_CM >250Ω across band, rising with frequency ================================================================================ FAILURE MODES ================================================================================ SYMPTOM: Very high SWR (even with G5RV properly tuned) ROOT CAUSE 1: Trifilar winding misaligned (one wire drifted) SOLUTION: Carefully inspect winding, verify all three strands parallel ROOT CAUSE 2: Core overheated (enamel cracked, internal short) SOLUTION: Test with ohmmeter (should be open between wires) If shorted, unwind and replace core SYMPTOM: Excessive heating during transmission ROOT CAUSE 1: High CM current (unbalanced antenna system) SOLUTION: - Verify G5RV is properly installed (equal leg lengths) - Check counterpoise or ground plane - Add secondary 1:1 choke if necessary ROOT CAUSE 2: High insertion loss adding heat SOLUTION: - Reduce transmit power (9:1 baluns run hot at full power) - Ensure potting is thermally conductive (silicone preferred) - Mount balun on metal bracket for heat dissipation SYMPTOM: Multiband antenna works only on some bands ROOT CAUSE: Turns ratio optimized for specific frequency SOLUTION: - G5RV relies on tuner to handle impedance variation - If tuner can't match, may indicate bad balun connection - Verify all three trifilar wires have continuity SYMPTOM: Pattern null in wrong direction ROOT CAUSE: High CM current not being suppressed SOLUTION: - Check Z_CM with NanoVNA (should be >250Ω) - If Z_CM low, core may be damaged or saturated - Verify turns count matches winding table ================================================================================ POWER HANDLING ================================================================================ FT-240-43 single core, 9:1 balun: Continuous (CW): 400 W @ 50°C ambient Peak (SSB): 600 W (transient, watch for heating) Thermal rise: ~25°C @ 400W, ~45°C @ 700W For 160M operation (higher loss): Recommend FT-240-43×2 stacked (doubles core area, halves loss) Thermal rise: ~20°C @ 400W (improved) Cooling strategies: - Aluminum mounting bracket (acts as heat sink) - Potting with thermal compound (not regular epoxy) - Ensure balun has airflow (don't enclose tightly) - Monitor core temperature during high-power sessions ================================================================================ DESIGN EQUATIONS ================================================================================ Turns ratio for 450→50Ω transformation: N_ratio = sqrt(450/50) = sqrt(9) = 3:1 Use 4:12 (ratio = 3.0, Z-ratio = 9.0) ✓ Or 3:9 (ratio = 3.0, Z-ratio = 9.0) for higher frequency ✓ Insertion Loss: L_dB ≈ 0.15 + 0.003 × f_MHz (FT-240-43, 9:1 configuration) Example @ 14.2 MHz: L ≈ 0.15 + 0.043 = 0.19 dB Example @ 3.75 MHz: L ≈ 0.15 + 0.011 = 0.16 dB (but practice ≈ 0.30 dB at 80M) Common-Mode Impedance: Z_CM = 2π × f × (AL × N_total²) / 10000 where N_total = N_primary + N_secondary For 4+12=16 turns: Z_CM ≈ 665Ω @ 80M ================================================================================ CONSTRUCTION NOTES ================================================================================ Mechanical Assembly: - 16 wire turns on single core is tight packing - Wind evenly to avoid bunching or gaps - Final assembly should be stable (no loose wires) Thermal Management: - Potting with silicone recommended - Avoid epoxy (poor thermal conductivity, may crack) - Thermal interface compound optional (between core and potting) Enclosure Design: - Larger box than 4:1 or 6:1 (more material, thermal mass) - Aluminum enclosure preferred (thermal sink effect) - Ventilation holes (1/8" minimum) for air circulation - Drain hole (1/16") to prevent moisture accumulation Field Installation: - Mount as close to G5RV feedpoint as practical - Keep coax output short (minimize impedance discontinuity) - Use quality connectors (stainless steel recommended) - Apply strain relief on all cable connections Spare Parts: - Keep extra FT-240-43 cores (can retrofit existing winding) - Stock #14 enameled wire (for field rewinding) - Pre-crimped connectors (SO-239, BNC) - Thermal potting compound (not regular epoxy) ================================================================================ G5RV ANTENNA SYSTEM ================================================================================ The 9:1 balun is THE classic match for G5RV antennas. G5RV Configuration: - 102 feet total (dipole section) - 34 feet of 450Ω ladder line (flat-top coupler) - 9:1 balun at base of ladder line - Coax from balun to tuner/receiver Performance: - Works 80M, 40M, 20M, 10M (primary bands) - Reports of 160M, 15M, 12M, 6M with tuner (not resonant) - Takeoff angle: ~25–30° (good for DX) - Gain: ~5–7 dBi @ 20M (excellent for all-band antenna) Impedance variation: - Each band exhibits different feedpoint impedance - Tuner required for efficient matching - 9:1 balun converts 450Ω ladder line to 50Ω for tuner input SWR at antenna: - Before balun: Varies widely (high SWR on ladder line acceptable) - After balun/tuner: <2:1 achievable on most bands ================================================================================ COMPARISON: 9:1 vs 4:1 vs 6:1 ================================================================================ Feature 9:1 Trifilar 6:1 Trifilar 4:1 Guanella ────────────────────────────────────────────────────────── Impedance 450→50Ω 300→50Ω 200→50Ω Loss @ 80M 0.30 dB 0.18 dB 0.20 dB Z_CM @ 80M 700Ω 750Ω 200Ω Winding Turns 4+12=16 5+12=17 bifilar pairs Power (400W) Thermal limits Adequate Adequate Primary Use G5RV, ladder Window line Dipole feeds Cost Estimate ~$16 ~$15 ~$18 G5RV users: 9:1 is PREFERRED (designed specifically for G5RV) Ladder line users: 6:1 better (lower loss, slightly better CM) ================================================================================