# LoRa APRS ESP32 APRSDroid bluetooth modem and LoRa APRS-IS iGate
Amateur radio ESP32 based LoRa APRSDroid KISS Bluetooth modem and LoRa APRS-IS iGate server.

![alt text](images/pinouts.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. By having two clients you can not only send your position, but also send and receive APRS messages.
- **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 **433.775MHz** as per https://vienna.iaru-r1.org/wp-content/uploads/2019/01/VIE19-C5-015-OEVSV-LORA-APRS-433-MHz.pdf
- 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 **2 seconds** to decode with as lower level as possible, use https://github.com/tanupoo/lorawan_toa to make calculations
  - lora bandwidth **CfgBw**, 125 kHz
  - lora spread factor **CfgSpread**, 12 (should decode down to -20dB, choosen with the goal for minimum signal decode)
  - 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 TCXO** 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**, for example, let client and server run for an 30-60 minutes and if server reports err: -1500, then set client frequency to about 1000 kHz less, e.g. instead of 433.775 set it to 433.774, this will give couple of additional dB

# Test Results
![alt text](images/setup.png)
- Antennas
  - Client: rubber duck antenna or mobile antenna on a car roof
  - Server: 7 element UHF yagi indoors
- Range (20 KHz channel width and 11 spreading factor, also got similar results with 125 kHz and 12 SF)
  - **About 7 km** when server is 30m above the ground and client is 2m above the ground with rubber duck antenna or inside a car
  - **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 (smaller packets, about 50 bytes), see APRSDroid discussions on compressed corrdinates support and custom branches
    - https://github.com/ge0rg/aprsdroid/pull/159
    - https://github.com/ge0rg/aprsdroid/issues/170
    - https://github.com/sh123/aprsdroid/tree/aprsdroid_compressed
    - https://github.com/sh123/aprsdroid/tree/aprsdroid_compressed_gradle
- Polarization
  - Using **horizontal polarization** improves successful decoding probability and receiving range