Turn a motor and read voltage

I wonder if anyone can help me please as I'm hopeless at coding?
I want to make a motor driven magnetic loop antenna and have it tuned by a large variable capacitor. I need the motor to turn through one revolution while recording the voltage from a vswr sensor and then return to the position where the voltage was lowest and stop.

I'm sure it's quite easy for you guys but my brain hurts from thinking about it. The motor can be either a servo or stepper as long as it can return accurately to the correct position. It would be great to have it read the frequency from the radio and have it track but one step at a time.

Thanks in advance.


You need some form of rotary transducer. Map signal level against transducer position then select transducer position that equates to signal minimum and drive motor to that position

If you need a full 360 degrees of motion you will have to be very careful with your choice of servo. Most of them only have about 180 deg of travel. Sail Winch servos can rotate through about 3 full revolutions. I don't know if anyone makes specific 360 deg servos. A continuous rotation servo would not be suitable as it has no position control.

If you can get a suitable servo it would be the simplest to work with both mechanically and from a programming point of view.

A stepper motor would be my next choice as you can count its steps and easily return to any specific position. But, as well as the motor, you need a stepper motor driver. Have a look at the links below for more background info.

If you use an ordinary DC motor you will also need a motor driver (a continuous rotation servo is a DC motor and motor driver combined) and you will need a rotary encoder to identify the position of your antenna. From a programming point of view this will be the most complex.

Stepper Motor Basics
Simple Stepper Code