================================================================================ SCHEMATIC: 1kW OIL-COOLED DUMMY LOAD TM-DL-1KW-OIL Rev A ================================================================================ RESISTOR NETWORK — 50 OHM, 1000W 20x non-inductive resistors: 1000 ohm, 50W each, in parallel N-Type Connector (SO-239 acceptable only at HF) | CENTER STUD | +---------+---------+ | | | [Bank A] [Bank B] [Bank C] [Bank D] ...5 banks x 4 resistors R1-R4 R5-R8 R9-R12 R13-R16 R17-R20 | | | | +---------+---------+---------+ | GROUND BUS / CHASSIS BANK LAYOUT (each bank = 4 resistors around center stud): View from above, one bank: N (North resistor) | W --+-- E 4 resistors at 90-deg intervals | around center conductor ring S All hot ends to inner ring (to stud) All cold ends to outer ring (to chassis) Inner ring diameter: 20mm (connects to stud) Outer ring diameter: 80mm (connects to chassis) FULL ASSEMBLY CROSS SECTION: +---------+ Lid (with fill plug + pressure relief + temp probe port) | OIL | | R17-R20 | ---- Bank D (top, 250mm from base) | | | R13-R16 | ---- Bank C (195mm from base) | | | R9-R12 | ---- Bank B (145mm from base) | | | R5-R8 | ---- Bank A (95mm from base) | | | R1-R4 | ---- Bank bottom (50mm from base) | | | [N-Jack]| ---- Connector (base, center) +---------+ Base plate (Al, 6mm thick, 200mm x 200mm) Container: 150mm x 150mm x 300mm welded aluminum box Wall thickness: 3mm minimum OR: Stainless steel food pan (hotel pan) with custom lid Total oil volume: ~4.5 liters VOLTAGE/CURRENT LEVELS AT 1kW: V_rms = sqrt(1000 x 50) = 223.6 Vrms V_peak = 316 V peak I_rms = sqrt(1000/50) = 4.47 Arms through load Current per resistor = 4.47/20 = 0.224 A (in 1000R: P = 0.224^2 x 1000 = 50W) DIELECTRIC STRESS: 316V peak on center stud to can wall (approx 50mm clearance) Electric field: 316V / 50mm = 6.3 kV/m Mineral oil dielectric: 30,000 kV/m (>>6.3 kV/m) -- ADEQUATE MARGIN DIRECTIONAL COUPLER (integrated): Resistive bridge coupler, 20 dB, 1 MHz - 500 MHz (See sch_dir_coupler.txt for full schematic) Forward power port: SMA female, panel mount on enclosure side Reflected power port: SMA female, panel mount on enclosure side Coupler board: 50mm x 30mm, FR4, mounted inside enclosure lid THERMAL MODEL: At 1kW continuous: Oil temp rise: dT/dt = P / (m_oil x Cp_oil) = 1000 / (4.5 x 0.86 x 1800) = 1000 / 6966 = 0.144 C/second Time to 80C limit from 25C ambient: t = (80 - 25) / 0.144 = 382 seconds = 6.4 minutes At 1kW with natural radiation from aluminum walls: Wall area: 2x(150x300) + 2x(150x300) + 150x150 = ~0.23 m^2 Radiation: ~15W/C above ambient for polished aluminum Steady state: T_ss = 25 + 1000/15 = 92C (exceeds limit) CONCLUSION: 1kW requires either: (a) Duty cycle <= 30% (10 min on, 23 min off) (b) External forced-air cooling across aluminum walls (c) Oil circulation pump (aquarium pump, 5 L/min adequate) Recommended: Operate 1kW with oil pump circulation + external radiator. At 500W continuous, no cooling required. At 1kW: 10-minute maximum continuous. PROTECTION CIRCUITS: Over-temperature relay: K1: DPDT relay, 12VDC coil, NC contacts in antenna switch line TH1: 10k NTC in oil, monitored by comparator circuit or CYD At T > 95C: relay opens, disconnects TX from load Red LED indicator for fault state Power indicator: Green LED via 10k in series to indicator port on coupler board Illuminates when RF present (detected by forward power detector) PARTS LIST ---------- Qty Reference Value/Part Number Description --- --------- -------------------- --------------------------- 20 R1-R20 1000R 50W non-induct. Ohmite RH-50E1K or equiv (ceramic body, NON-INDUCTIVE) 1 J1 N-type, chassis mount Panel bottom center 1 J2,J3 SMA female, flange Forward/reflected coupler ports 1 -- Al box 150x150x320mm 3mm wall welded Al (custom or weld from plate) 5 -- Cu ring set, ID=18mm Inner bus rings, per bank 5 -- Cu ring set, ID=90mm Outer bus rings, per bank 1 -- Brass stud 5/16-18 Center conductor stud, 300mm 1 TH1 10k NTC stainless Oil temp probe 200mm 4.5L -- Naphthenic mineral oil 1 -- Aquarium pump 5L/min Optional oil circulation (12V) 1 K1 DPDT relay 12V Over-temp shutdown 1 -- Dir. coupler PCB See sch_dir_coupler.txt ================================================================================