How to work out (Hfe) AC Forward current transfer ratio for ZTX650 BJT Transistor?
This might help: -



So, look up what the transition frequency is and imagine a line falling at 6dB/octave crossing the point marked \$f_T\$. The horizontal/flat line (at lower frequencies) is the "DC" hFE and, where the 6dB/octave line crosses the horizontal line, that is the place where hFE starts to decrease with frequency.

Basically this means that you can assume hFE applies to AC up to the point where the 6dB/octave line intercepts it.

The typical \$f_T\$ for the ZTX650 is 175 MHz and if hFE is (say) 128 at DC, 7 octaves below 175 MHz is where the two lines intercept i.e. ~1.4 MHz: -