The maximum usable frequency of an ionospheric layer at

The maximum usable frequency of an ionospheric layer at 60º incidance and with 8 MHz. The critical frequency is—

Maximum usable frequency, muf = f_c sec θ
where, given θ i = 60º
f_c = 8 MHz
Now, muf = 8 × 10⁶ × sec 60º
= 16 MHz