I’ve been trying to figure this out for ages and finally solved it. The documented sim events for COM radios use BCD16, so it’s not possible to set e.g. 120.855 - it’s truncated to 120.85 when converting. I’ve even seen workarounds in some people’s apps where they send the value followed by small increment events.
But it turns out there are some undocumented events which work:
COM_STBY_RADIO_SET_HZ
COM2_STBY_RADIO_SET_HZ
NAV1_STBY_SET_HZ
NAV2_STBY_SET_HZ
Set the DWORD value as raw Hz, e.g. for 120.855 send 120855000.
The NAV radios obviously don’t require this precision, but it’s nice to be able to use the same interface for them all.
Hope this helps someone!