/magloop_controller

Arduino magnetic loop antenna controller and 3d printed high voltage sliding capacitor

Primary LanguageOpenSCADMIT LicenseMIT

Magnetic loop antenna capacitor controller

Magnetic loop antenna capacitor controller based on

  • OpenSCAD project to generate custom sliding variable high voltage capacitors with two predefined configurations
  • Arduino Nano
  • L298N stepper driver
  • EM-290 stepper from Epson printer
  • HC-06 bluetooth serial controller for remote control using Bluetooth console application from the phone or PC
  • Generated high voltage 3d printed slide capacitor printed with PETG plastic (up to ~15kV and 130pF)
    • Plate sizes are ~70x55 mm
    • Capacitor dimensions are 60x70x80 mm
    • Plate spacing 5 mm
    • 14 plates
    • Worm gear is M4
    • Can handle 100W CW without arcing (tested with 0.9m loop) and continous 50W operation in FT8
    • Capacitance range ~5-130 pF
    • Can tune ~9-29 MHz with 0.9m loop
  • Second test generated medium voltage 3d printed slide capacitor up to ~6 kV and higher 400pF capacitance

Serial commands

On successful command execution "ok" is returned when operation was successfully completed or "err" if command was unsuccessful. Next commands are supported:

  • Movements
    • p: park to initial 0 position, automatically performed when powered on
    • u, uu, uuu: go/tune up to higher frequency (5/50/500kHz steps)
    • d, dd, ddd: go/tune down to lower frequency (5/50/500kHz steps)
    • freqkhz, frequency in kHz where to move capacitor, should be used after calibration procedure completion
  • Calibration
    • t: print calibration table
    • c[freqkhz]: store current minimum swr position into given calibration frequency cell
    • s: save calibration table

Configuration parameters (capctrl.h)

  • ConfigSpeed: stepper speed, default is 64
  • ConfigStep(5|50|500)kHz: number of steps for tune up/down commands for 5/50/500kHz steps
  • ConfigMaxPos: end position of capacitor, maximum number of steps, default is 5200
  • ConfigCalPoints: number of calibration points, default is 23
  • ConfigCalAddr: EEPROM start address where calibration data is stored, default is 0x0
  • ConfigStepCompensate: number of steps for reverse compensation when changing direction

Photos

  • Large capacitor 15kV/130pF

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  • Medium size capacitor with lower maximum voltage, but larger capacitance 6kV/400pF

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  • Test magnetic loop antenna, 1m loop diameter, 40mm tube diameter, fed using inductive coupling from smaller loop and 1:1 balun

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