================================================================================ SCHEMATIC: TRANSMISSION LINE TRANSFORMERS (TLT) TM-HYB-001 Rev A Guanella and Ruthroff types; wideband 1:1 balun, 4:1, 9:1 unun Coverage: 1.5 MHz – 50 MHz (HF/low-VHF); for hybrids and phased arrays ================================================================================ OVERVIEW -------- Transmission line transformers (TLTs) use the transmission line mode (Lecher line) rather than transformer flux linkage, giving decade-wide bandwidth. Unlike wound transformers, TLTs are efficient from 1.5 MHz to 50 MHz+ with the correct core material. Types covered: 1. Guanella 1:1 Balun — balanced/unbalanced; 50Ω:50Ω 2. Guanella 4:1 Balun — balanced/unbalanced; 200Ω:50Ω 3. Ruthroff 4:1 Unun — unbalanced; 200Ω:50Ω (voltage-adding, narrower BW) 4. 9:1 Unun — 450Ω:50Ω (for open-wire to coax) 5. 180° Hybrid TLT — in-phase/antiphase split for phased arrays 6. Wideband 90° Hybrid TLT — quadrature split, 1–50 MHz CORE SELECTION --------------- Material Fair-Rite Mix Use Case Perm (µ) -------- ------------- -------- -------- Mix 43 #43 HF general, 1–50 MHz 950 Mix 61 #61 HF/low VHF, 10–200 MHz 125 Mix 31 #31 1–100 MHz (broadband) 1500 Mix 73 #73 AM broadcast/low HF 2500 Amidon 43 BN-43-202, BN-43-3312 950 RECOMMENDATION: Mix 43 for 1.5–30 MHz phased array applications. Mix 61 for 15–50 MHz and above. Binocular cores (BN-xx-202, BN-xx-3312) are compact and allow bifilar/trifilar winding without transformer geometry constraints. WIRE TYPES ----------- For 50Ω TLT (coax-wound): use RG-174 or RG-316 wound on core. For low-Z TLT (twisted pair): use #26 AWG bifilar (Teflon-coated preferred). For high-power (100W+): #18 AWG bifilar or RG-58 on large cores. Twisted pair impedance ≈ 50–100Ω (depends on wire spacing and coating). Coax-wound impedance = coax characteristic impedance. ================================================================================ 1. GUANELLA 1:1 BALUN ================================================================================ PURPOSE: Converts unbalanced (coaxial) to balanced (balanced twin-lead/dipole). Provides common-mode isolation without impedance transformation. Essential for phased dipole arrays to prevent feedline radiation. SCHEMATIC: COAX IN BALANCED OUT (Unbalanced, 50Ω) (Balanced, 50Ω each leg to center) │ ────┼──── CENTER CONDUCTOR ─────────────────── (+) OUT │ │ │ [T1: Coax wound on Mix-43 toroid or binocular core] │ │ (this is the transmission line; not a transformer) │ ────┼──── COAX BRAID ──────────────────────── (−) OUT │ │ │ [Core choke action: common-mode impedance Z_cm = jωµN²A/l] The coax (or twisted pair) forms a transmission line through the core. Differential mode (inside coax): passes unchanged, core does nothing. Common mode (outside coax): sees high impedance from core → blocked. WINDING PROCEDURE (BN-43-202 binocular core): 1. Thread RG-174 or #26 bifilar through both holes of BN-43-202. 2. Pass 6 turns through both apertures. 3. Connect inner conductor of coax to one balanced terminal. 4. Connect outer conductor (braid end) to other balanced terminal. 5. Center tap of outer conductor: connect to ground at input side only. Schematic symbol: IN ─────[====== 6t on BN-43-202 ======]───── OUT(+) GND ────[ ]───── OUT(−) COMMON-MODE IMPEDANCE vs FREQUENCY (BN-43-202, 6 turns, Mix 43): f (MHz) |Z_cm| (Ω) 1 100 3 300 7 700 14 1200 28 1800 50 1200 (permeability falling off) For Z_cm > 500Ω: effective common-mode suppression. For Z_cm > 1000Ω: excellent suppression (>25 dB). INSERTION LOSS: < 0.1 dB from 1.5 to 30 MHz. POWER RATING: 200W PEP on BN-43-202; 1 kW on FT-240-43. SWR: < 1.1:1 from 1.5 to 30 MHz when terminated in matched balanced load. ================================================================================ 2. GUANELLA 4:1 CURRENT BALUN ================================================================================ PURPOSE: 200Ω balanced input to 50Ω unbalanced output (or vice versa). Used with folded dipoles (200Ω feedpoint) or 4-square arrays. SCHEMATIC: 200Ω BALANCED IN 50Ω OUT (+) ────────────[===T1: 6t, BN-43-202===]──────── CENTER CONDUCTOR [ ] │ (−) ────────────[===T2: 6t, BN-43-202===]──────── BRAID │ GND (bottom of T2) Two identical TLT units (T1, T2) in series at input, parallel at output. Series connection: presents 2 × 50Ω = 100Ω? No — Correct Guanella 4:1 topology: T1 and T2 each are transmission lines with Z0 = 50Ω. T1: + input terminal to (+ output) through line. T2: − input terminal to (− output = GND) through line. Series at input: V_in appears across both lines in series → 2V_in total. Parallel at output: currents add, voltage is V_in → impedance ratio 4:1. Detailed wiring: Input (+) ──── T1 start (+) ────[T1]──── T1 end (+) ──── Output (+) Input (−) ──── T2 start (+) ────[T2]──── T2 end (+) ──── Ground T1 end (−) tied to T2 start (−): common midpoint. Output: T1 end (+) to center conductor; T2 end (−) to ground (braid). Actual layout on BN-43-202: Wind two separate 6-turn coaxes (or bifilar pairs) on two cores. Connect in series at high-Z side, parallel at low-Z side. OR: wind both on a SINGLE BN-43-3312 (larger binocular) — 2 × 6t. POWER RATING: 200W PEP on BN-43-202; 1 kW on BN-43-3312. BANDWIDTH: 1.5 MHz – 40 MHz (−0.5 dB limits). ================================================================================ 3. RUTHROFF 4:1 UNUN ================================================================================ PURPOSE: Unbalanced 200Ω to 50Ω impedance transformation (no balanced output). Simpler than Guanella but narrower bandwidth (voltage-summing type). SCHEMATIC: 200Ω INPUT ──────────── WINDING START │ [T1: 6t bifilar on T-200-2 or FT-114-43] │ 50Ω OUTPUT ─────────────┤ │ (delayed output line adds to direct) INPUT + DELAYED OUTPUT = 2V → 4:1 Z ratio In detail: V_in applied across winding 1 (series arm). Winding 2 (parallel arm) adds same voltage in series with output. Output voltage = 2 × V_in / 2 = V_in (voltage halved, current doubled). Z_out = Z_in / 4. This "voltage adder" action is inherently frequency-limited by the propagation delay through the line (works well when line ≤ λ/8). Maximum useful frequency: ~40 MHz for 30 cm line on core. WINDING TABLE: Power (W) Core Turns Wire gauge --------- ---- ----- ---------- 50 FT-50-43 8t #26 AWG bifilar 100 FT-114-43 8t #22 AWG bifilar 500 FT-240-43 8t #18 AWG bifilar or RG-58 coax 1500 T-300-43 10t RG-58 (coax-wound) ================================================================================ 4. 9:1 UNUN (50Ω TO 450Ω) ================================================================================ PURPOSE: Matches coaxial 50Ω feed to 450Ω open-wire ladder line or end-fed wire antennas in a phased array context. TOPOLOGY: Guanella type using three 50Ω lines in series (input) and parallel (output). Z ratio = 3² = 9:1. 3 LINES IN SERIES at 450Ω input: Line 1: V₁ Line 2: V₂ Line 3: V₃ V_total = V₁ + V₂ + V₃ = 3V 3 LINES IN PARALLEL at 50Ω output: Total current = 3I Z_out = V / 3I = Z_line / 3 = 50 / 3 ≠ 50 → use Z_line = 150Ω for 3:1 turn ratio → Actually for 9:1: use 3 identical 50Ω lines; Z_out = Z_in/9. Simplified winding: 3 × 6-turn RG-174 sections on FT-114-43, connected series at high-Z end and parallel at 50Ω end. BANDWIDTH: 1.5–30 MHz, ±0.5 dB. POWER RATING: 100W on FT-114-43; 500W on FT-240-43. ================================================================================ 5. 180° HYBRID FROM TLT (WIDEBAND HF PHASE SPLITTER) ================================================================================ PURPOSE: Provides 0° and 180° outputs from single input, 1.5–50 MHz. Used in phased array to feed elements 0° and 180°. SCHEMATIC: IN (50Ω) ──────┬───────────────────────────── OUT-A (0°, −3 dB) │ [T1: 1:1 Guanella balun on BN-43-3312] │ └───────────────────────────── OUT-B (180°, −3 dB) Actually: use a center-tapped toroid winding: IN ──[50Ω]──┬────────────────────── OUT-A (0°) │ [T1 primary: N turns, FT-114-43] │ center tap → GND (reference) [T1 secondary: N turns, same core] │ └────────────────────── OUT-B (180°) The secondary winding reversal gives the 180° phase inversion. Each output is −3 dB (half power into matched 50Ω loads). T1 winding: 10t bifilar #22 AWG on FT-114-43. Center tap of secondary to shield/ground. Isolation between OUT-A and OUT-B: >20 dB (core provides). Bandwidth: 2–50 MHz, amplitude balance < 0.3 dB, phase balance < 2°. ALTERNATIVE with isolation (for use as hybrid, not just splitter): Add 100Ω resistor between OUT-A and OUT-B (Wilkinson-style isolation). This dissipates reflected power if outputs are mismatched. ================================================================================ 6. WIDEBAND 90° HYBRID FROM TLT (HF QUADRATURE SPLITTER) ================================================================================ PURPOSE: Provides 0° and −90° outputs, 1–50 MHz wideband. Used for circular polarization feed or phased array endfire element. APPROACH: Wideband all-pass constant-resistance phase shift network. Not a transmission line quarter-wave section (which is narrowband). Instead: use a Schiffman coupler or all-pass network. SCHIFFMAN PHASE SECTION (WIDEBAND 90° PHASE DIFFERENCE): Uses a coupled transmission line section in a ring topology. Broadband: achieves ±5° phase error over 5:1 bandwidth. Difficult to implement at HF with lumped elements. PRACTICAL HF QUADRATURE HYBRID: Use a lumped all-pass network pair: Section A: 0° passthrough (reference path) Section B: −90° all-pass network at center frequency All-pass bridged-T for −90°: IN ──[R]──────────────────────── OUT (0°) │ [L] ─[parallel C]─ GND (series L in parallel with shunt C) The all-pass network introduces −90° at resonance: At ω₀ = 1/√(LC): phase = −90° exactly. R = Z0 = 50Ω for impedance match. L = Z0 / ω₀ = 50 / (2πf₀) C = 1 / (Z0 × ω₀) = 1 / (2πf₀ × 50) Same as Wilkinson arm values — a −90° all-pass filter. Amplitude: flat (all-pass passes all frequencies at 0 dB). Phase error: ±10° over 2:1 bandwidth (adequate for most arrays). COMPONENT TABLE (50Ω all-pass 90° section): Band f₀(MHz) L(µH) C(pF) Application ---- ------- ----- ----- ----------- 160M 1.85 4.30 1719 λ/4 substitute for 4-square 80M 3.75 2.12 849 80M 4-square array 40M 7.15 1.113 446 40M 2-element phased array 20M 14.175 0.561 225 20M driven/reflector array 15M 21.225 0.375 150 15M 2-element endfire This all-pass network gives the 90° phase shift used in the reference NEC model phased arrays (see nec_models directory). PARTS LIST — TLT BALUN FAMILY (ONE UNIT) ------------------------------------------ Ref Qty Value/Part Description --- --- ---------- ----------- T1 1 BN-43-202 Binocular core, Mix 43 (1:1 balun) or FT-114-43 Toroid, Mix 43 (higher power) Wire — #22–#26 AWG Teflon-coated magnet wire (bifilar) or RG-174 For coax-wound version J1 1 SO-239 or SMA Unbalanced (coax) port J2, J3 2 Binding posts Balanced port (or SMA with matching) Housing — see openscad files Weatherproof enclosure TORQUE / SEALING NOTE FOR OUTDOOR USE: Apply 3M Scotch-88 tape over all connections. Pot with urethane conformal coat. Use stainless or gold-plated SMA connectors. Mount with sealant around connector flanges. ================================================================================