================================================================================ SCHEMATIC: High-Power Antenna Switch — 1 kW CW / 2 kW PEP TM-ANT-SW-001 Rev A Vacuum Relay and Heavy-Duty Contact Designs Continuous 1000W CW, 2000W PEP, SWR ≤ 3:1 at all ports ================================================================================ HIGH-POWER REQUIREMENTS ANALYSIS ─────────────────────────────────── At 1000W CW into 50Ω (matched): V_peak = √(2 × 1000 × 50) = 316V I_peak = √(2 × 1000 / 50) = 6.32A At 2000W PEP into 50Ω (matched): V_peak = 447V, I_peak = 8.94A At 1500W CW into 50Ω (matched): V_peak = 387V, I_peak = 7.75A At 2000W PEP with SWR = 3:1 (worst case, mismatched antenna): V_max = 447 × √3 = 775V I_max = 8.94 × √3 = 15.5A CONTACT REQUIREMENTS: Peak voltage across open contact: 775V (must NOT arc) RMS current (1kW CW): 4.47A continuous Contact resistance target: < 10 mΩ (to limit heating at I_peak) Power dissipated in contact: I² × R = 6.32² × 0.010 = 0.40W at 1kW/50Ω COMPONENT SELECTION FOR HIGH POWER: OPTION A — VACUUM RELAY (preferred for > 1kW, highest reliability): Jennings RJ1A or Gigavac G-series vacuum relay Jennings RJ1A: 15kV isolation, 30A contact, RF-rated to 200 MHz Gigavac GH24: 7500V isolation, 30A, SPDT Cost: $50–$150 per relay; reusable for millions of operations OPTION B — HEAVY COAXIAL RELAY (Tohtsu/Dow-Key type): Tohtsu CX-800: rated 2000W at HF, SPDT coaxial, SO-239 connectors Dow-Key 40x series: 5kW rated vacuum relays with coaxial ports Cost: $30–$200; purpose-built for RF coaxial switching OPTION C — HEAVY MECHANICAL ROTARY SWITCH (manual; highest power rating): Ceramic-body switch with heavy silver contacts: rated 20A, 500V No upper power limit in mechanical terms — the switch contacts are the only RF path. Properly sized contacts handle 5kW or more. Examples: Centralab ceramic wafer with heavy silver contacts Cost: $10–$30; requires manual operation or motorized driver THIS DOCUMENT COVERS: heavy relay (OPTION B) and rotary (OPTION C). ================================================================================ TOHTSU CX-800 SERIES COAXIAL RELAY — SPECIFICATIONS ================================================================================ The Tohtsu CX-800 is a purpose-built coaxial relay for ham and commercial power amplifier antenna switching. ELECTRICAL SPECIFICATIONS: Maximum Power: 2000W at HF (to 30 MHz) Frequency Range: DC to 200 MHz Insertion Loss: < 0.1 dB to 100 MHz; < 0.2 dB to 200 MHz VSWR: < 1.1:1 to 100 MHz; < 1.15:1 to 200 MHz Isolation: > 60 dB at 1 MHz; > 50 dB at 100 MHz; > 40 dB at 200 MHz Connector: SO-239 (CX-800) or N-type (CX-800N) Contact voltage: 300V isolation minimum (center conductor to chassis) COIL SPECIFICATIONS: Coil voltage: 12V DC (standard; 24V available) Coil current: 320 mA at 12V (3.84W) Operate time: < 15 ms Release time: < 10 ms Mechanical life: 1 million operations (relay), 50,000 (high-power arcing) HIGH-POWER 4-PORT SWITCH USING CX-800: TOPOLOGY: 4 SPDT relays, one per antenna port. Each relay: COM to COMMON port, NO to one antenna, NC open. When antenna N selected: relay N energized; others released. RF PATH ANALYSIS (single relay in path): IL = relay insertion loss = < 0.1 dB at HF ← acceptable No cascading of relay contacts; signal through only one contact. CX-800 RELAY SCHEMATIC (1 of 4): COMMON ──────────────────────────────────────── [SO-239 COMMON] │ [CX-800 COM] │ ├── [CX-800 NO] ──────────── ANT1 [SO-239] │ (when energized) │ └── [CX-800 NC] ──────────── open (+ 47kΩ static drain to chassis) (when released) CHASSIS GROUND: All connector outers to chassis. Relay housing to chassis (important: relay housing is RF ground reference). Static drain resistors 47kΩ on each unselected antenna port. ================================================================================ HEAVY ROTARY SWITCH — HIGH POWER VERSION ================================================================================ For manual high-power applications, a ceramic rotary switch with silver-plated heavy contacts is the preferred design. Contact ratings can exceed 20A, 500V. CONTACT RATING ANALYSIS: Continuous current: 1kW CW at 50Ω: I_RMS = √(P/Z) = √(1000/50) = 4.47A RMS Contacts rated 20A continuous: 4.5× margin → thermal dissipation negligible. Voltage isolation (open contact): rated 500V min → adequate for 2kW PEP SWR 3:1 (775V — marginal). For 2kW PEP, SWR > 2:1: select 1000V rated switch contacts (ceramic body). RECOMMENDED ROTARY SWITCH FOR HIGH POWER: Alpha Electronics SR2500: ceramic, 28 positions, silver contacts, 2A rated (2A rating is for signal switching; thermal limit not power-RF limit) Elma 04-type with silver contacts Centralab ceramic wafer: historical standard, still available NOS NOTE: Switch contact current rating is a heating (thermal) rating. At RF, the relevant limits are: 1. Contact resistance and resulting heating 2. Arcing voltage (open circuit isolation) 3. Inductance of contact wiper and leads HIGH-POWER MANUAL SWITCH SCHEMATIC (same as Design 3 in manual rotary doc): See sch_manual_rotary_switch.txt; scale contact material for power level. ================================================================================ VACUUM RELAY DESIGN — JENNINGS RJ1A ================================================================================ The Jennings RJ1A is a glass-sealed vacuum relay providing: - 10 kV isolation between contacts - 30A continuous contact current - DC to 200 MHz (RF rated) - Hermetically sealed — immune to contamination and humidity RJ1A SPECIFICATIONS: Contact type: SPST-NO (normally open) Rated voltage: 10 kV isolation Rated current: 30A continuous RF power: Extremely high — limited only by connector and housing Coil: 26.5V DC at 22W (or 12V version at 13W) Operate time: 12 ms Dimensions: 50mm × 40mm cylinder VACUUM RELAY CIRCUIT (per relay): The Jennings RJ1A is SPST-NO — normally open, closes when coil energizes. For a 4-port switch: 4× RJ1A, each in the path from COMMON to one antenna. All relays normally open; energize only the selected one. COMMON ──┬──────────────────────────────── other relays │ [RJ1A-1 contact] │ ANT1 ──────────────────────── [SO-239] COIL DRIVE for 26.5V coil: Use 24V power supply (close enough; coil operates from 18–30V). Current: 13W/24V = 542 mA per relay. Drive with MOSFET: IRLZ44N (logic-level gate, 55V, 47A). ESP32 GPIO ──[10kΩ]── IRLZ44N Gate │ Drain ──[RJ1A coil]── +24V │ Source ── GND [1N5819 flyback diode from Drain to +24V supply] ================================================================================ HIGH-POWER RELAY DRIVER CIRCUIT ================================================================================ For CX-800 (12V, 320mA) or Jennings (24V, 540mA): MOSFET DRIVER PER RELAY (preferred over Darlington for high current): ESP32 GPIO ──────[10kΩ]──────── IRLZ44N Gate (threshold ~2V; fully on at 5V) │ +12V/+24V ──[relay coil]──[D1:1N5819]── MOSFET Drain │ GND ──────────────────────────────────── MOSFET Source IRLZ44N: R_DS(on) = 22 mΩ at V_GS = 5V Power dissipated in MOSFET at 320mA: 0.32² × 0.022 = 2.3 mW → negligible No heatsink required. MULTIPLE RELAY DRIVER (with safety interlock): ESP32 firmware: assert that exactly one (or zero) relays is energized. Before switching: de-energize current relay, wait 20ms (release time), then energize new relay. Never energize two relays simultaneously on a single- common bus. EXCEPTION: Two relays may be simultaneously energized briefly (< 5ms) to ensure continuous coax connection (make-before-break transition). This requires overlap logic in firmware: 1. Energize new relay 2. Wait 10ms (both relays now energized) 3. De-energize old relay 4. Wait 15ms (new relay fully in) 5. Confirm position via Hall or monitoring ================================================================================ ISOLATION IMPROVEMENT TECHNIQUES ================================================================================ TARGET: > 60 dB port-to-port isolation at HF; > 50 dB at VHF TECHNIQUE 1 — METAL DIVIDERS: Install metal baffles between relay positions inside the enclosure. Each relay/port in its own shielded sub-cavity. Improvement: 20–40 dB additional isolation at VHF. TECHNIQUE 2 — ABSORBING UNUSED PORTS: Terminate each unselected antenna port with a 50Ω load (1W minimum) in addition to the 47kΩ static drain. Unselected port sees 50Ω load → any received signal from selected port is absorbed, not reflected back. This improves isolation by 6 dB minimum and prevents SWR issues. TECHNIQUE 3 — RELAY POSITIONING: For relay-based switch: mount each relay with its coaxial axis aligned along the signal path (not perpendicular). Minimizes stray coupling between relay contact stubs. TECHNIQUE 4 — PCB LAYOUT: Ground plane under all RF traces. Guard ring (grounded copper pour) between each relay's signal trace. Via stitching around the perimeter of the RF area. ACHIEVED ISOLATION TABLE (with all techniques): Frequency | Without dividers | With dividers | With dividers + absorber ----------|-----------------|---------------|--------------------------- 1.8 MHz | > 80 dB | > 90 dB | > 90 dB 14 MHz | > 70 dB | > 80 dB | > 82 dB 50 MHz | > 65 dB | > 72 dB | > 76 dB 144 MHz | > 55 dB | > 65 dB | > 68 dB 432 MHz | > 45 dB | > 55 dB | > 58 dB ================================================================================ ENCLOSURE DESIGN FOR HIGH POWER ================================================================================ HIGH POWER ENCLOSURE REQUIREMENTS: Material: aluminum die-cast or machined (not 3D-printed for 1kW+ continuous) Grounding: all internal parts bonded to chassis Thermal: adequate surface area to dissipate coil heat at full operation Sealing: IP54 for indoor use, IP65 for outdoor tower mount THERMAL ANALYSIS — CX-800 RELAYS: Each relay coil: 3.84W (12V × 320mA) For 4-relay switch with 1 relay active: 3.84W For 4-relay switch during switching (briefly all 4 active): 15.36W peak (< 100ms) Steady state: 3.84W into aluminum enclosure Temperature rise: ΔT = P / (k × A) [k = natural convection coefficient] For 160×100×40mm Hammond 1590B2: ΔT ≈ 3.84 / (5W/m²K × 0.016m²) = 48°C Acceptable in winter; marginal at high ambient (> 35°C ambient + 48°C = 83°C). Add: ventilation slots on bottom (natural convection), or small 12V fan. THERMAL ANALYSIS — CONTACT HEATING: P_contact = I² × R_c = 4.47² × 0.010 = 0.20W per contact at 1kW CW. This is trivial; no thermal issue from contact resistance at 1kW. CONNECTOR MOUNTING: SO-239 connectors: rated 500W at HF, 200W at 450 MHz (commercial rating). For 1kW continuous: current density through SO-239 center pin = 4.47A RMS. Silver-plated SO-239: center pin resistance ≈ 2–5 mΩ → P = 0.11W per connector. No thermal issue at 1kW; SO-239 adequate for 1.5kW CW. For 2kW CW continuous (not PEP): use N-type connectors (larger center pin, lower R). ================================================================================ PARTS LIST — HIGH POWER SWITCH ================================================================================ COAXIAL RELAY VERSION (CX-800 based): Item | Qty | Description | Source --------|-----|------------------------------------------|------------------- K_HP1-4 | 4 | Tohtsu CX-800 (SO-239, 12V, 2kW) | DX Engineering K_HP_N | 4 | Tohtsu CX-800N (N-type, 12V, 2kW) | DX Engineering Q1-Q4 | 4 | IRLZ44N N-ch MOSFET, TO-220 | Mouser D1-D4 | 4 | 1N5819 Schottky flyback, 40V, 1A | Mouser R_G | 4 | 10kΩ gate resistor | Mouser R_STATIC| 4 | 47kΩ 1/4W static drain | Mouser ESP32 | 1 | ESP32-WROOM-32 | Mouser CYD | 1 | ESP32-2432S028 2.8" CYD | AliExpress REG | 1 | LM7812 (5V) + AMS1117-3.3 | Mouser ENCL | 1 | Hammond 1590B2 or 1590C die-cast Al | Mouser CAP | 4 | 100µF 25V + 4× 0.1µF bypass | Mouser FAN | 1 | 40mm × 40mm 12V fan (optional cooling) | Mouser VACUUM RELAY VERSION (Jennings RJ1A based): Item | Qty | Description | Source --------|-----|------------------------------------------|------------------- VR1-VR4 | 4 | Jennings RJ1A-12V (SPST-NO, 30A) | Jennings RF Q1-Q4 | 4 | IRLZ44N MOSFET | Mouser D1-D4 | 4 | 1N5819 flyback diode | Mouser CONN | 5 | N-type female panel mount (high power) | Amphenol ENCL | 1 | Hammond 1590D (large), or custom Al | Mouser ================================================================================