Here my project for an easy remote tuning.
1. the Arduino Sketch
2. the variable Air Capacitor
3. the Loop
4. the control box                    
                   

 

 

1. the Arduino Sketch:

#include <Stepper.h>
int SPU = 2048;
Stepper Motor(SPU, 3,5,4,6);  // its Stepper 28BYJ-48

int taste7 ;  // links langsam
int taste8 ; // rechts langsam
int taste9 ; // links schnell
int taste10 ; // rechts schnell


void setup() {

  pinMode(7, INPUT_PULLUP);
  pinMode(8, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);
  pinMode(10, INPUT_PULLUP);
// all button inputs are internal pulled up
// if press then goes to GND
}
void loop() {
  taste7 = digitalRead(7);
  taste8 = digitalRead(8);
  taste9 = digitalRead(9);
  taste10 = digitalRead(10);

// you can play by different values,
// setSpeed, step (nb of steps), 
// delay between the number of steps

// Links langsam, left slow
  while(taste7 == 0){
    Motor.setSpeed(1);
    Motor.step(1);
    delay(100);
    taste7 = digitalRead(7);
  }
 
// Rechts langsam, right slow
  while(taste8 == 0){
    Motor.setSpeed(1);
    Motor.step(-1);
    delay(100);
    taste8 = digitalRead(8);
  }

// Links schnell, left fast
  while(taste9 == 0){
    Motor.setSpeed(5);
    Motor.step(20);
//    delay(100);
    taste9 = digitalRead(9);
  }

// Rechts schnell, right fast
  while(taste10 == 0){
    Motor.setSpeed(5);
    Motor.step(-20);
//    delay(100);
    taste10 = digitalRead(10);
  }

}

2. the variable Air Capacitor
Material: 1mm Aluminium
Bearings: 4mm/9mm
Threaded rods: Brass M4
DIY design, calculation - only cut in a factory (Laser cut)
After choosing the size, I calculated first with a distance of 1mm (breakdown abt 6 kV - split) for a capacity of abt 23 pF (2 stator / 1 rotor).
After first assembling I measured 25 pF - not bad matched.
Now I use 5 mm distance this makes:
5 mm - rotor 1mm = 4mm -2 sides = 2mm - 3kV/mm = 6kV
Because of split = 12 kV - thats a lot...

 

3. the Loop
Material: RG-214 (similar RG-213 but silver coated surfaces)
Dia/per-meter: 1m / 3.1m
FeedLoop: AIRCELL7 Diameter abt 25cm
  
  
4. the control Box
3D printed Size w/d/h 60mm/80mm/30mm