LoRa APRS 433 MHz battery powered beacon

It has a WiFi Access Point for easy real time configuration.
It sends: ham callsign, GPS or fixed coordinates, altitude, Volts and mA

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This is a LoRa APRS Tracker working on the 433 MHz band.

It features an Access Point for real time configuration.

Its main use is to send a periodic beacon containing:
- Callsign
- GPS or fixed coordinates
- Altitude
- Battery voltage and current

Any received LoRa APRS packet, including the one repeated by a local digipeater, is displayed in the (very) small 0.96" display.

The packet format is perfectly compliant with and

The main suggestion came from a ham radio fellow: why not to use the following module from Bangood for our LoRa APRS 433.750 MHz project? It is quite cheap (35 Euros) and compact and it is said to be very reliable as well.

LILYGO® TTGO Meshtastic T-Beam V1.1 ESP32 433 Mhz
 WiFi Bluetooth ESP32 GPS NEO-6M SMA
18650 Battery with OLED - 433 MHz

This module has very distinctive features but the most interesting is the AXP192 IC, that lets the battery to  power supply the used components only, and at the right time only, saving a lot of energy from the LIPO 18650 battery. For instance, don't supply the GPS module when the tracker is in fixed mode i.e. it uses previously set latitude and longitude. The AXP192 charge the LIPO battery from the USB as well.

I found a few articles about LoRa modules with APRS software, but the closest to my idea was this one by peterus, that I happily forked.

  • The original rubber antenna must be tuned!

    Guido12/23/2021 at 10:36 0 comments

    Hi all!

    I've found that the original antenna of the LILYGO® TTGO T-Beam is tuned at around 470MHz and that at 433.750 MHz the return loss is -3dB (half power in transmission is lost).

    See how I solved in the "Details".


View project log

  • 1

    The original antenna is tuned around 470 MHz and therefore it ha a return loss of around -3dB at 433MHz. To tune it, you have 2 options. Without or With a Vector Network Analyzer.

  • 2
    Carefully remove the rubber cover

    Hold the SMA connector with a clamp and gently move the rubber cover until it gets away.

  • 3
    Stretch the metallic (mine is made of copper) spring to obtain a total length of 17 cm, including the SMA connector

View all 4 instructions

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