================================================================================ SCHEMATIC: Multi-Stage Surge Protection — GDT + MOV + TVS Diode TM-LSP-001 Rev A Three-Stage Coaxial Protection with < 0.1 dB Insertion Loss at 50 MHz Clamping Voltage: ≤ 60V; Peak Current: 10 kA; Response Time: < 1 ns (final stage) ================================================================================ MULTI-STAGE PROTECTION THEORY ────────────────────────────── A single protection device (GDT, MOV, or TVS) cannot simultaneously satisfy all protection requirements: - High peak current handling (kA range) → GDT or MOV - Fast response (< 1 ns) → TVS diode - Low residual clamp voltage (< 60V) → TVS diode - Low capacitance (< 5 pF for VHF) → GDT The solution is a three-stage cascaded clamp, with each stage optimized for one parameter. Decoupling inductors/resistors between stages prevent the slower stages from being bypassed by the faster stages. STAGE 1 — GDT (Coarse clamp, high current, ~100 ns): Handles the bulk of lightning energy (kA range) Clamps to V_arc ≈ 15–25V AFTER sparkover (but sparkover takes ~100 ns) During the 100 ns sparkover delay, voltage may reach 500–2000V on the line The following stages handle this pre-sparkover energy STAGE 2 — MOV / Zener (Medium clamp, medium speed, ~10 ns): Metal Oxide Varistor clamps voltage during GDT sparkover delay Handles ~1–10 kA impulse Clamping voltage: 150–400V (limited by MOV physics) Capacitance: 100–1000 pF (too high for VHF — use ONLY in HF design) STAGE 3 — TVS Diode (Fine clamp, fast, < 1 ns): Transient Voltage Suppressor clamps to precise voltage (V_BR + V_f × 1.3) Handles 1–500A impulse (much less than GDT but sufficient for residual energy) Clamping voltage: 30–200V (precisely controlled) Capacitance: 5–500 pF (must select low-C type for VHF) Response: sub-nanosecond (protects against LEMP: Lightning Electromagnetic Pulse) DECOUPLING BETWEEN STAGES: Series inductors L1, L2 prevent Stage 3 (fast/low-C) from absorbing energy before Stage 1 (slow/high-C) has time to clamp. L1 (between Stage 1 and Stage 2): 47 nH to 100 nH L2 (between Stage 2 and Stage 3): 22 nH to 47 nH These inductors add series impedance → insertion loss. For HF-only use: L1 = 100 nH, L2 = 47 nH (acceptable IL) For VHF use: L1 ≤ 33 nH, L2 ≤ 22 nH (keep XL < 5Ω at 144 MHz) ================================================================================ COMPLETE 3-STAGE SCHEMATIC — HF VERSION (1.8–54 MHz) ================================================================================ ANTENNA ────[IN]──────────────────────────────────[OUT]──── TO SHACK SO-239 SO-239 CENTER CONDUCTOR PATH: IN ─── [L1: 100nH] ─────── [L2: 47nH] ────────────── OUT center │ │ center [GDT1] [TVS1] 90V/2.5kA 60V/500A │ (SMBJ54A pair) [MOV1] │ 150V/1kA │ │ │ CHASSIS GND ─────────┴────────────────┘─────────── CHASSIS SHIELD PATH: IN shield ──────────────────────────────────────── OUT shield Both bonded to chassis ground (zero impedance path) DETAILED SCHEMATIC — FULL THREE-STAGE: IN_center──┬──L1(100nH)──┬──L2(47nH)──┬──── OUT_center │ │ │ (not used [GDT1] [TVS1+TVS2] at this 90V,2.5kA back-to-back node) │ 60V TVS (SMBJ54CA) [MOV1] │ 150V,1kA │ │ │ CHASSIS ────────────────┴─────────────┘ NOTE: MOV1 is connected from junction of L1/L2 to chassis. GDT1 is connected from input side of L1 to chassis. TVS1 (bidirectional) is connected from output of L2 to chassis. Stage activation sequence during a 2kV, 10kA lightning surge: t=0 to 100 ns: Voltage rises toward 2kV; L1+GDT1 slow the surge. MOV1 activates at ~200V (forward conduction); clamps to ~200V. TVS1 activates at ~60V; limits OUT to ~60V. t=100 ns: GDT1 fires (sparkover), clamps IN to ~20V arc voltage. Surge current diverts through GDT1 to chassis. t > 100 ns: GDT1 in full conduction; handles remaining kA current. TVS1 sees only residual oscillation; handles < 500A. ================================================================================ MULTI-STAGE SCHEMATIC — VHF VERSION (50–450 MHz, LOW CAPACITANCE) ================================================================================ For VHF, MOV stage is ELIMINATED (too much capacitance). Only GDT + TVS with minimal inductance values. IN_center──┬──L1(22nH)──┬──L2(10nH)──┬──── OUT_center │ │ │ │ [GDT1] [TVS1] │ 90V/2.5kA SMBJ54CA │ (1.0pF) 5pF typ │ │ │ CHASSIS ───┴─────────────┴─────────────┘ TVS DIODE CAPACITANCE AT VHF: Standard SMBJ54CA: capacitance ≈ 130 pF → unacceptable above 30 MHz Must use RF-optimized TVS: Semtech SM6T39CA: 5 pF, 39V, 600W → good to 300 MHz Bourns TISP4095F3BHJR: array type, 3 pF per element ON Semi ESD9L5.0ST5G: 0.35 pF, ESD rated (lower current, 200A peak) For 144–432 MHz use ESD9L5.0ST5G (0.35pF) or similar: Insertion loss at 432 MHz with 0.35pF: IL ≈ 0.003 dB (negligible) Peak current: 200A (adequate for residual after GDT clamps main surge) VHF-SPECIFIC TVS SELECTION: Part | V_BR | I_peak | C_j | f_max | Application ---------------|-------|--------|--------|----------|------------------ SMBJ54CA | 54V | 500A | 130pF | 20 MHz | HF only SM6T39CA | 39V | 600W | 5pF | 300 MHz | HF+VHF to 2M ESD9L5.0ST5G | 5V | 200A | 0.35pF | 1.5 GHz | VHF/UHF/microwave CDSOT23-T24C | 24V | 30A | 2pF | 600 MHz | low-energy ESD BZW04-P18B | 20V | 3.5kA | 50pF | 80 MHz | high-current HF PSOT-36A | 36V | 600W | 1pF | 1 GHz | 70cm-23cm ================================================================================ CLAMPING VOLTAGE ANALYSIS — WHAT REACHES THE RADIO ================================================================================ Without protection: Direct strike surge: 2000–30000 V at antenna feedpoint. Induced surge (nearby strike): 200–2000 V. Both: immediate destruction of radio front-end. Single GDT (90V) only: Pre-sparkover (0–100 ns): 200–2000 V passes through unimpeded. Post-sparkover (> 100 ns): clamped to ~20V. Problem: fast semiconductors in modern radios damaged in < 10 ns. Single GDT is NOT adequate protection for modern equipment. Single TVS (54V) only: Sub-ns response; immediately clamps to ~75V. But: TVS handles only ~500A; lightning carries kA → TVS destroyed on first hit. Single TVS is NOT adequate for direct/nearby lightning. MULTI-STAGE (GDT + TVS): Stage 1 (GDT): Diverts kA surge to ground; sparkover in ~100 ns. Stage 2 (L decoupling): Slows down energy reaching TVS; TVS sees < 500A. Stage 3 (TVS): Clamps remaining residual to 60V in sub-ns. RESULT: Radio sees ≤ 75V, < 500A → modern radio front-ends survive. Note: No passive protection guarantees survival of direct lightning attachment. The multi-stage design is protection against induced surges and nearby strikes (the vastly more common scenario for properly installed ham antennas). CLAMPING PERFORMANCE TABLE: Event type | V at radio | I at radio | Radio survives? ------------------------|-----------|-----------|------------------ Static discharge only | <1V | <1mA | Yes (trivial) ESD (human body touch) | <5V | <1A | Yes (with TVS) Power line induction | <20V | <100mA | Yes Nearby strike (100m) | <60V | <200A | Yes (multi-stage) Direct induced (10m) | <75V | <500A | Probably (marginal) Direct attachment | >1000V | >5kA | No (disconnect antenna) CARDINAL RULE: Disconnect antenna before thunderstorms. No arrestor is a substitute for physical disconnection during active lightning. ================================================================================ INSERTION LOSS — MULTI-STAGE DESIGN ================================================================================ HF Version (L1=100nH, L2=47nH, GDT=1pF, TVS=130pF): Freq (MHz) | IL GDT (dB) | IL L1+L2 (dB) | IL TVS (dB) | Total IL (dB) -----------|-------------|---------------|-------------|------------- 1.8 | <0.001 | <0.001 | <0.001 | <0.001 3.5 | <0.001 | <0.001 | <0.001 | <0.001 7.0 | <0.001 | <0.001 | <0.001 | <0.001 14.0 | <0.001 | 0.002 | 0.004 | 0.007 21.0 | <0.001 | 0.005 | 0.009 | 0.015 28.0 | <0.001 | 0.009 | 0.016 | 0.026 50.0 | 0.001 | 0.029 | 0.052 | 0.082 ← within spec VHF Version (L1=22nH, L2=10nH, GDT=1pF, TVS=5pF): Freq (MHz) | IL GDT (dB) | IL L1+L2 (dB) | IL TVS (dB) | Total IL (dB) -----------|-------------|---------------|-------------|------------- 50.0 | 0.001 | 0.002 | <0.001 | 0.003 144.0 | 0.002 | 0.016 | 0.001 | 0.019 222.0 | 0.004 | 0.038 | 0.002 | 0.044 432.0 | 0.022 | 0.142 | 0.006 | 0.170 ← exceeds spec ← reduce L values for 70cm Note: For 432 MHz, use L1=10nH, L2=4.7nH to bring total IL under 0.1 dB. ================================================================================ PARTS LIST — MULTI-STAGE PROTECTION ================================================================================ HF VERSION (1.8–54 MHz): Ref | Qty | Value/Part | Description | Source ------|-----|-----------------|-------------------------------|-------- GDT1 | 1 | B88069X1140B232 | 90V, 2.5kA, 1.0pF GDT | Mouser MOV1 | 1 | Littelfuse V150LA10BP | 150V MOV, 1kA, 10mm | Mouser TVS1 | 1 | SMBJ54CA | 54V bidirectional TVS, 600W | Mouser L1 | 1 | 100 nH | Chip inductor, 0805, 1A min | Coilcraft 0805CS-R10XJLB L2 | 1 | 47 nH | Chip inductor, 0805, 1A min | Coilcraft 0805CS-47NXJLB J1,J2 | 2 | SO-239 silver | Panel mount UHF-F | Amphenol PCB | 1 | FR-4, 50Ω trace | 50Ω microstrip between stages | design per trace width ENCL | 1 | 3D printed ASA | See openscad file | VHF VERSION (50–432 MHz): GDT1 | 1 | B88069X1140B232 | 90V, 2.5kA, 1.0pF GDT | Mouser TVS1 | 1 | SM6T39CA | 39V, 5pF TVS for VHF | Mouser L1 | 1 | 22 nH | 0805 chip inductor | Coilcraft L2 | 1 | 10 nH | 0805 chip inductor | Coilcraft J1,J2 | 2 | N-type female | Panel mount, IP67 | Amphenol 82-836 ================================================================================