The heartbeat message shall be sent on a periodic basis every
15 seconds. This
message is intended to be used by servers to detect the presence
of a client and also the unexpected disappearance of a client
and by clients to learn the schema negotiated by the server
after it receives the initial heartbeat message from a client.
The heartbeat message shall be sent on a periodic basis every 15 seconds. This message is intended to be used by servers to detect the presence of a client and also the unexpected disappearance of a client and by clients to learn the schema negotiated by the server after it receives the initial heartbeat message from a client.
See WSJT-X source.