Reading this thread piqued my intrigue, so went and had a look at the manual for my FT817ND. The CAT command for getting frequency is there, but has the feeling of having been added as an afterthought. It looks bodged
Issue CAT command 03 with 4 dummy bytes
It should return 5 bytes of data with frequency and mode.
BUT BUT BUT ...
In footnotes, firstly it states "Do not use this command when using alkaline batteries or the supplied FNB-85 Ni-MH battery pack"
Then it goes on to state "Send a 5-byte dummy data (such as 00 00 00 00 00) first when sending this command
Why the battery pack should affect this particular CAT command I shudder to think