Tiny 2m beacon

Following up on his  FSK beacon prototype, Ross set about making a miniature lightweight version to fit on one of Nick's "TinyThing" boards (based around an Arduino Pro Mini).

This has a smaller code-space than the ESP32, so uses an adapted version of the "FlexTrack" code to send just RTTY on 2m using the SX1278 radio (which is designed for operation at 433MHz, so it needs a custom low-pass filter to reduce the harmonic energy when transmitting at VHF). 

This beacon is testing on 144.021MHz, transmitting just 10 milliwatts. Every 15 seconds it sends 2FSK "RTTY" with a shift of 488Hz at a rate of 100 baud, 7N2 (7-bit ASCII with No parity and 2 stop-bits).  It decodes well using Fldigi (or DL-Fldigi), although not with HorusGUI.

Each telemetry frame consists of the following elements:
Callsign, frame_number, time, latitude, longitude, altitude, speed, direction, satellites, checksum