August 23, 2021

Arduino Magnetic Loop Antenna Controller

from hackster.io

Ham operations may employ a magnetic loop antenna, where a resonant antenna loop is literally looped together, connected by a high-voltage variable capacitor.

These heavy duty variable capacitors are physically rotated for tuning. As the antenna is normally located some distance from the operator, there needs to be a way to remotely turn the capacitor, a perfect job for a stepper motor and Arduino setup.

For his ham rig, Jose B.O. used a CNC shield attached to an Arduino Uno. This was placed in a nice enclosure, along with an I2C 16x2 LCD display and optical encoder for control.

The device can advance steppers to preset positions via interface buttons, and rotate back and forth in a more “analog” manner via the encoder knob.

The rig is meant to accommodate up to three loop antennas, via outputs that would traditionally control the X, Y, and Z axes of a CNC machine.

Microswitches are also added to the rig to define upper and lower limits of the capacitor, matching the behavior of many CNC machines. A cutoff function for the stepper motor is available if it’s causing interference, and there’s a backlash compensation function is available if needed.

You can see it demonstrated in the video below, and more info is available via the project's write-up.