================================================================================ SCHEMATIC: 500W OIL-COOLED DUMMY LOAD (CANTENNA STYLE) TM-DL-500W-OIL Rev A ================================================================================ RESISTOR NETWORK — 50 OHM, 500W 10x non-inductive resistors in parallel: 500 ohm, 50W each N-TYPE CONNECTOR (panel mount, bottom of can) | CENTER PIN (threaded stud) | +------+------+------+------+------+ | | | | | | R1 R2 R3 R4 R5 (same 5 more: R6-R10) 500R 500R 500R 500R 500R 50W 50W 50W 50W 50W | | | | | +------+------+------+------+------+ | GROUND BUS (ring / chassis) = outer shell of N connector = can body (all conductive) SIDE VIEW — INTERNAL LAYOUT: +----------------------------------+ <-- Sealing lid (printable or Al) | | Pressure relief: 1/8" NPT plug | Mineral oil fill | | (food grade, naphthenic type) | | | | R6 R7 R8 R9 R10 | <-- Top bank, mounted on top ring | | | | | | | | +---+---+---+---+ | | | | | [Ground bus ring] | | | | | +---+---+---+---+ | | | | | | | | | R1 R2 R3 R4 R5 | <-- Bottom bank, on connector stud | | | | [Ground ring] | | | | | [N-Jack] ---CENTER STUD--- | <-- N connector, bottom center +----------------------------------+ | [N-Jack] | <-- Bottom plate (Al or brass) +----------------------------------+ DIMENSIONS (1-gallon paint can equivalent): Can OD: 152 mm Can height: 285 mm Oil volume: ~3.5 liters Oil weight: ~3.0 kg (mineral oil density 0.86 kg/L) RESISTOR MOUNTING DETAIL: 10x Ohmite RH series or equivalent, 500R 50W ceramic body, axial leads Bottom 5 (R1-R5): Leads bent and soldered to center stud and ground ring Top 5 (R6-R10): Same but inverted, also to center stud (extended) and ring This "double-decker" arrangement minimizes lead length and inductance. All resistors fully submerged in oil. CRITICAL: Resistor body must NOT touch can wall. Maintain 5mm clearance. Resistors must be fully immersed in oil (oil level above top bank). Do not operate if oil level falls below top bank. CONNECTING STUD: Brass rod, 1/4"-20 thread, 200mm long Connected to N-jack center pin with silver solder All R hot ends soldered to stud at appropriate heights Stud isolated from can lid by PTFE standoff GROUND RING (per bank): Copper ring, OD = 120mm, 3mm wide x 3mm thick All R cold ends soldered to ring Ring soldered to can interior bottom for lower bank Ring soldered to can wall via copper strap for upper bank GROUND STRAP: Copper braid, 10mm x 2mm, from upper ring to N-jack shell Keep as short as possible (<30mm) OIL FILL PROCEDURE: 1. Complete all internal wiring and verify 50 ohm DC resistance. 2. Clean interior with isopropyl alcohol. Dry completely (heat gun). 3. Fill with naphthenic mineral oil (transformer oil or food-grade) until oil is 15mm above top resistor bank. 4. Install pressure relief plug (1/8" NPT brass fitting with 0.5mm orifice or loose cap that vents when oil boils/expands). 5. Do NOT seal completely. Oil expands ~7% from 20C to 100C. A sealed airtight container will build pressure. OIL SPECIFICATIONS: Type: Naphthenic mineral oil, Type II transformer oil Alternatives: Pure mineral oil (food-grade), Mobil Diala S4 ZX-I Avoid: Motor oil (sulfur compounds degrade insulation) Synthetic oil (flammable at high temperatures) Water or glycol (corrosion, low dielectric strength) Dielectric: >30 kV/mm (new oil) Flash point: >130C (mineral oil) Volume required: 3.5 liters (1-gallon can size) 1.5 liters (1-quart can size, 200W version) TEMPERATURE MONITORING: NTC thermistor, 10k @ 25C, stainless steel probe, 150mm insertion depth Inserted through 1/4"-28 drilled/tapped hole in can lid Sealed with PTFE tape on threads Connected to CYD monitor or dedicated meter Temperature limits: Normal operation: <80C oil temperature Warning threshold: 85C (LED/alarm) Shutdown: 95C (relay opens antenna switch) Oil flash point: 130C (mineral oil) -- DO NOT APPROACH PERFORMANCE SPECIFICATIONS -------------------------- Impedance: 50 ohm nominal Power: 500W continuous (adequate oil volume and ventilation) 1kW for 60 seconds (SSB) Duty cycle: 100% at 500W with adequate thermal mass 50% at 750W Frequency: DC to 1 GHz (N connector, SMT-optimized build) SWR (DC-30 MHz): < 1.05:1 SWR (30-500 MHz): < 1.15:1 SWR (500 MHz-1GHz):< 1.5:1 PARTS LIST ---------- Qty Reference Value/Part Number Description --- --------- -------------------- --------------------------- 10 R1-R10 500R 50W non-inductive Ohmite RH-50E500R or TE Connectivity NKKB50-500 1 J1 N-type female chassis Amphenol 82-835 or equiv 1 -- 1-gallon paint can Steel, clean, food-grade seal 1 -- Brass rod 1/4-20 8" Center conductor stud 2 -- Copper ring 120mm OD Ground bus rings 1 TH1 10k NTC, stainless Oil temperature probe, 150mm 3.5L -- Mineral oil Naphthenic, transformer grade 1 -- 1/8" NPT brass fitting Pressure relief plug 1 -- PTFE standoff 1/4-20 Center stud isolation at lid 1 -- Enclosure See openscad/enclosure_cantenna.scad (lid and base adapter only; can body is metal) ================================================================================