Experimental QRO magloop slide variable capacitors (3 and 5mm spacing, ~3-90 pF)

Last crawled date: 4 years, 3 months ago

Two experimental magnetic loop antenna variable capacitors. Built to understand if such 3d printed capacitors are feasible and what are their limits with PETG filament for QRO operation.
Print at your own risk, may need some manual tuning with rasp or try to print with 0.1 precision. Was using prototype/test loop built by using some leftovers from construction work and 3d printed center holder.
Both cover ~3-95 pf, maximum power is around 50W (CW) for small capacitor and 100W (CW) for large on 0.9 M loop, tunes continuously from ~9 to 29 MHz. Tested large capacitor at 50W FT8 for multiple iterations on 30M band and it was slightly warm without noticeable SWR degradation. With better spiral coupling matching got about SWR 1.05 at minimum.
Small capacitor contains 11 (5 + 6) 0.5 mm 30x55 mm aluminium plates connected with M3 screw and nuts for each plate. Plate spacing is 3 mm. Large capacitor plate sizes are 50x60 mm and plate spacing is 5 mm.
I also have home made butterfly capacitors, they can sustain 100 W, but they cannot continously cover all required range starting from small capacitance, because their minimum capacitance is rather large for larger maximum capacitance.
Construction time is about 30-40 minutes when models are already printed.
Added models for EM-290 stepper (from old epson printer) holder and shaft for linking between motor and M3 worm gear.