My modern remote loop will sit in the backyard while I tune it from the shack. It will also let me play with some new toys.
Back in the 1970’s, I used a loop antenna for listening to distant AM radio stations. That antenna has long since disappeared, so I think I will build a new one before all the AM broadcast stations go dark here in North America. This more modern version of the loop antenna will be remotely tunable for direction and frequency.
Building this modern remote loop will provide the chance to play with some new toys. First, servo motors from rotating and tilting the loop antenna. I have a fair amount of experience with stepper motors on my 3D printer and CNC machine. Stepper motors are good for position control but they have one weakness: they are usually controlled “open loop”. This means that while you tell the motor to move a certain number of steps in a direction, you have no feedback as to where they really are. This is why it is important to home 3D printers, to find the “zero points” along each axis, before you start printing.
Servo motors on the other hand are “closed loop” devices. They always know where they are. Modern servos are controlled using PWM or pulse-width modulation. Microcontrollers like Arduino can send PWM signals to servo motors for exact positioning. I will combine two servo motors with some sort of panning and tilting mount for the loop antenna.
Modern Remote Loop Electronics
The second new toy to be enjoyed is the ModeMCU. This is a module containing the ESP8266-12E WiFi system that has lots of outputs and can be programmed just like the Arduino. The NodeMCU will be mounted on the antenna. It will communicate with my ham shack by WiFi, just like for my last project – the magnetic transmitting loop.
In addition to controlling pan-tilt servo motors, the ModeMCU will also provide a control voltage for a variable capacitor to tune the loop. This time, however, rather than using a motor to turn a physical capacitor, I will use the microcontroller to generate a voltage to tune a varicap or electronically tunable capacitor. The NodeMCU will provide a digital signal to a digital to analog converter (DAC) to arrive at the correct voltage for tuning the antenna to resonance.
So, there’s the idea for my next project. Time to start building.