Consider waveforms $$\cos(2 \pi f_1 t + \theta)$$ and $$\cos(2 \pi f_2 t), (f_1 > f_2)$$, to be used for non-coherent binary FSK signalling. If the symbol duration is T seconds, and $$\theta$$ is constant arbitrary angle from 0 to $$2 \pi$$, what is the minimum separation required between $$f_1$$ and $$f_2$$ for non-coherent, orthogonal FSK?

A

$$f_1 - f_2 = \frac{1}{T}$$

B

$$f_1 - f_2 = \frac{2}{T}$$

C

$$f_1 - f_2 = \frac{1}{4T}$$

D

$$f_1 - f_2 = \frac{1}{3T}$$