I'm using pixhawk and simonk esc trying to calibrate esc. I have fs i6b receiver and i6 transmitter.
From RC of pixhawk to ppm/ch1 are connected.
What should I do ?
is there any need of PPM encoder ?

yes you need ppm encoder and connect the receiver to the encoder and then connect it to PPM on Pixhawk

What is the receiver you are using ia6 or ia6b?
ia6 only has PWM. You need PPM encoder.
If you have ia6b then it has PPM and ibus but you need to bind your receiver in PPM/ibus mode in order to use it.

@Balakrishna Reddy Thanks ...
I've I6B and tried with ppm mode and it worked ..