Adding ARRL Field Day Support

[wcheng95]

In an FT8 project I’m working on, I’ve integrated an existing FT8 library and it’s almost plug-and-play. The main missing piece is ARRL Field Day (contest exchange) support (i3.n3 = 0.3/0.4). I plan to add it myself, so I’m opening this thread to discuss the expected message flow and any corner cases.

Some features are more a concern of the front end / UI layer, but I want to make sure the library itself is robust and protocol-correct.

Standard ARRL Field Day FT8 exchange (WSJT-X style)
(Grid intentionally omitted to avoid ambiguity with FD exchanges.)
t0: CQ FD AG6AQ
t1: AG6AQ W1AW 2F CT
t2: W1AW AG6AQ R 3A SCV
t3: AG6AQ W1AW RR73
t4: W1AW AG6AQ 73

Possible 1-slot shorter variant
t0: CQ FD AG6AQ 3A SCV
t1: AG6AQ W1AW 2F CT (or AG6AQ W1AW R 2F CT)
t2: W1AW AG6AQ RR73
t3: AG6AQ W1AW 73

I’d appreciate comments on:
whether the shortened flow is log-safe and commonly accepted,
whether using R 2F CT in t1 causes any decoder or auto-sequencing issues, and
any recommended handling for repeats or partial copy in an FD-specific state machine.

73,
Wei AG6AQ