1) Typically most developers open one slave channel per each ANT+ master channel they wish to listen to as it's the lowest power & easiest option. If you need to listen to more than 8 master channels then you have 3 options:
i) Use a
background scanning channel, preferable with high duty search on the
ANTUSB-m or at least using the fast search waveform on
other devices.
ii) Use
continuous scanning mode.
iii) Emulate a background scanning channel by re-wildcarding & re-opening a regular slave channel every time it
pairs to a master.
Shared channels will not work most of the time as shared channels are a method of pairing tens of thousands of slave channels to a single master channel, whereas most ANT+ device profiles are simple master channels themselves which you need to receive from many of and cannot be modified for interoperability.
2) To maintain ANT+ interoperability, only parameters which the profile specifies can change, can be modified. You may build a private implementation alongside ANT+ interoperable channels in order to build a bigger or different topology depending on your use case.
Members typically build receivers using continuous scanning mode/background scanning channel to receive from more devices than 8.
3) Sync is not a broadcast profile, instead it only performs
ANT-FS which uses burst messaging for
FIT file transfer. Burst messages are designed for throughput over coexistence, and will interfere with regular broadcast messaging, thus it's been placed on a separate frequency with a separate network key.
Profiles only impose the format of the 8-byte message content, and channel parameters.
ANT gives you other tools to build topologies on top of these.
Cheers
