Puts "F4BPO is on air 14,074,000 FT8 IC-7300" on hrdlog.net's front page while
the station is operating, which is what HRDLog's own "Automatic HRDLog ON AIR"
setting does.
The endpoint and its field names come from HRDLog's own library
(github.com/iw1qlh/HRDLOG-net-library, HrdProtocol.SendOnAirAsync): OnAir.aspx,
with Frequency in Hz, Mode, Radio, Callsign, Code and App. Read rather than
guessed — an invented endpoint would have produced a switch that silently did
nothing.
HTTPS where that library uses plain HTTP: the upload code is a credential and
has no business crossing the network in clear, and the sibling NewEntry
endpoint on the same host already serves TLS.
A heartbeat every two minutes, not a change notification — HRDLog drops a
station from the list when it stops hearing from it. Silent when switched off,
unconfigured, or when the rig reports no frequency: announcing 0 Hz would say
the operator is on air on nothing. Failures are logged, never toasted; a
broadcast the operator did not ask for at that instant must not interrupt them
every two minutes on a flaky link.
Its own switch beside auto-upload rather than folded into it: this is a live
status and needs the rig readable, not a QSO.