- 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
- it is also possible to use **other KISS APRS clients** over Bluetooth serial, just use `rfcomm` on Linux to setup serial over Bluetooth and put up AX25 interface with `kissattach`, then use any existing Linux APRS clients, such as `Xastir` or even run `TCPIP` over AX25
- **RF to APRS-IS gating**, it will connect to WiFI and will forward received APRS positions from RF LoRa 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 (could be enabled or disabled from config)
All work was done on ESP32-WROOM with custom made LoRa shield, if your ESP32 board is compatible then it should work, but there might be need to redefine pinouts to LoRa module if it differs (see further description in Software Setup section), currently pinouts are connected from LoRa to ESP32-WROOM as (SS/RST/DIO0 could be redefined in loraprs_service.h):
- for server mode fill `cfg.AprsFilter`, see http://www.aprs-is.net/javAPRSFilter.aspx for various formats, do not include `filter` directive, just space separated values
- change `cfg.LoraFreq` 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 experiment with different bandwidths/spread factors then modify values in `initializeConfig()`, 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 `cfg.LoraBw`, 125 kHz (also tested with 20.6 KHz and SF9 with frequency correction)
- use 80 MHz ESP32 frequency in Arduino SDK, it will prolong battery life when operating portable, higher CPU speed is not required, there are no CPU intensive operations
- or calibrate clients based on server frequency drift report by changing `cfg.LoraFreq`, 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
- alternatively automatic calibration could be done on server or client side by enabling automatic frequency correction by setting `cfg.EnableAutoFreqCorrection` to `true`, might be suitable for experiments where only one client is operating or if server broadcast messages, so clients can correct their frequency
-`cfg.EnableBeacon` set to `true` to enable periodic beacons specified in `cfg.AprsRawBeacon` with period specified in `cfg.AprsRawBeaconPeriodMinutes` into RF and APRS-IS if `cfg.EnableRfToIs` is enabled
- With such low power it is very important to have antenna SWR close to 1, many rubber duck antennas are claimed to be 433MHz, but they do not resonate at that frequency at all or resonate only when attached to its native large handheld transceiver, which has enough metal inside to behave like a counterpoise, these antennas have SWR 2 or higher. Check your antenna on antenna analyzer before using, add counterpoise if needed or better to use dipole or halo home made antenna for that matter
- Successful decodes down to **-19.75dB** below the noise floor when using compressed APRS coordinates (smaller packets, about 50 bytes, **32 bytes without PATH, speed, altitude**), see APRSDroid discussions on compressed corrdinates support and custom branches
- Monitor your planned frequency, such as 433.775 MHz for ISM device activity, if there is strong interference from other users tune up or down it to minimize interference
