Remotely operated Antenna Tuner - in use

In my last post I described the system I have recently put together to remotely tune ➿ the antenna 🗼 I use for the MF 630m ( medium wave) amateur band. The images below show the outdoor parts of the system now deployed and in operation with the antenna.

Base of antenna showing tuner, coil, element & support

A usb rechargeable power-bank 🔋 provides power for the remote unit and motor. I made a protective cover ( yellow object ) for the stepper-motor to keep it dry.

Container cover removed to show remote unit & power-bank

While trying it all out for the first time when using my transmitter I was able to re-tune 🔁 the antenna as I changed transmission frequency, from the operating position indoors.  All parts of the system are performing well. I am very pleased with the results.

Remotely operated Antenna Tuning

My inverted-'L' ( end-fed Marconi ) type antenna🗼for the 630m 📻 amateur band uses a variometer tuned loading coil ➿ at its base, which has to be adjusted to maintain antenna resonance when the transmitter changes frequency. Manual adjustment has always been possible; but never convenient as the coil is situated 35m from the house. So I devised a method for 'tuning' the antenna remotely, building on my experience using  LoRa and BluetoothⓇ 📶 in some previous projects.

Indoor unit (display active), remote unit, stepper motor & coil

The setup comprises an indoor unit for the LoRa transceiver and BluetoothⓇ server and remote units consisting of  another LoRa transceiver and stepper motor. TTGO LoRa Esp32 micro-controller boards are used.

App "Step_Match" opened

My custom App "Step_Match" for a smart-phone📱 connects to the server "Step_Tune" with BluetoothⓇ. Each time 'Step CW +' or 'Step CCW -' is tapped a command is sent to the indoor unit, then via LoRa to the remote receiver to drive the motor shaft clockwise or counter-clockwise by 5ͦ . Cumulative motor steps, number of clicks and degrees of rotation, ( relative to a half-way position at zero ), are updated. The motor actually makes 28 steps for each 5ͦ of shaft rotation, 2048 steps per revolution at a speed of 2rpm. 

The 3-D printed 3cm diameter toothed wheel  ( 24 teeth ) fitted to the motor shaft engages with a 4cm diameter toothed wheel ( 32 teeth ) on the variometer coil adjustment shaft; this gear ratio being 1/1.33. So the variometer shaft rotates 3.75ͦ per click. A initial check just holding the motor in position confirmed that it developed enough torque.

I temporarily placed the 'remote units' outdoors next to the antenna. The 868MHz LoRa link worked perfectly. Everything is now ready for use with the antenna. 

 

LoRa = Long Range ( a low bit rate, low power, long range digital wireless data technology ).

🗼 An image showing the original antenna was posted on 11 September 2012.