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