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.
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| 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.
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| 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.
