esp32_loraprs/README.md

# Experimental LoRa APRS ESP32 APRSDroid bluetooth modem and LoRa APRS-IS iGate
Tiny experimental amateur radio ESP32 based LoRa APRSDroid KISS Bluetooth modem and LoRa APRS-IS iGate server.

![alt text](https://www.smart-prototyping.com/image/data/5_community/WIFI/101770%20Ra-01/2.png)

Can be used in two modes: 
- **as a LoRa APRS client**, you need to use APRSDroid application (https://aprsdroid.org), connect to the modem using bluetooth, data will be re-transmitted through the LoRa radio, this is similar to APRSDroid micromodem - https://unsigned.io/micromodem/, received data will be sent back to the APRSDroid using bluetooth
- **as a LoRa APRS iGate server**, which connects to your WiFI and forwards received LoRa APRS positions into the APRS-IS network, it also reports client signal level, by appending it into the APRS comment, so you can see your signal reports in different locations

# Software Dependencies (install via libraries)
- Arduino ESP32 library: https://github.com/espressif/arduino-esp32
- LoRa arduino library: https://github.com/sandeepmistry/arduino-LoRa
- Arduino Timer library: https://github.com/contrem/arduino-timer

# Software Setup
- when setting up APRSDroid, use **"TNC (KISS)"** connection protocol in Connection Preferences -> Connection Protocol
- go to esp32_loraprs.ino and make next changes based on your requirements
  - comment out / remove **LORAPRS_CLIENT** define if you are planning to run server mode for APRS-IS iGate
  - for server mode fill **LORAPRS_WIFI_SSID** and **LORAPRS_WIFI_KEY** with your WiFI AP data
  - for server mode fill **LORAPRS_LOGIN** and **LORAPRS_PASS** with APRS-IS login callsign and pass
  - change **LORAPRS_FREQ** if you are planning to use different frequency or if planning to calibrate clients, currently it is set to **432.500MHz**, which is 70cm band APRS frequency in IARU-1 region, see http://info.aprs.net/index.php?title=Frequencies
- if you are planning to use different esp32 pinouts then modify loraprs.h
  - lora module SS, **CfgPinSs**, pin 5
  - lora module RST, **CfgPinRst**, pin 26
  - lora module DIO0, **CfgPinDio0**, pin 14
- if you are planning to experiment with different bandwidths/spread factors then modify loraprs.h, with current parameters APRS packet time on air is around **5 seconds** to decode with as lower level as possible, use https://github.com/tanupoo/lorawan_toa to make calculations
  - lora bandwidth **CfgBw**, 20 kHz (to fit into standard 25 kHz channel)
  - lora spread factor **CfgSpread**, 11 (should decode down to -17.5dB)
  - lora coding rate **CfgCodingRate**, 7
  - lora output power **CfgPower**, 20 (max 20 dBm ~ 100mW, change to lower value if needed)
- use 80 MHz ESP32 frequency in Arduino, it will prolong battery life when operating portable, higher CPU speed is not required, there are no CPU intensive operations
- uses LoRa built-in checksum calculation to drop broken packets
- note, that there a is **significant frequency drift** on temperature changes for different modules, you need to use external TXCO if you are planning to use modules for narrow bandwidths less than 125 kHz or calibrate clients based on server frequency drift report by changing LORAPRS_FREQ, which is OK for experiments

# Test Results
- Antennas
  - Client - rubber duck antenna or mobile antenna on a car roof
  - Server - UHF yagi indoors
- Range (20 KHz channel width and 11 spreading factor)
  - **About 4 km** when server is 30m above the ground and client is 2m above the ground with rubber duck antenna
  - **About 13 km** when server is 30m above the ground and client is at some higher point ~40m above the ground with rubber duck antenna
  - **About 17km** maximum (non-reliable) between base and mobile station with antenna on the car roof
- Signal levels
  - Successful decodes down to **-17.5dB** below the noise floor when using compressed APRS coordinates