This is quite simple for Axis Q7401.
Make an account at axis website.
Go to the video server page and access the support section. There's a place where you can download a PTZ file for your video server. There's a lot of PTZ protocols and Pelco is there. You just have to check you firmware release to match the PTZ file.
At the video server you can go to the PTZ menu and load the PTZ file you donwloaded from Axis website.
You have to check your PTZ address (ID) and the serial baud rate (2400, 4800 or 9600), parity, bits and stop bits to match video server serial settings. You can change it on the encoder.
When you load a Pelco protocol file at Axis encoder the default settings is Pelco D (2400, N, 8, 1). At advanced PTZ settings you can change from D to P and at the Port configuration (serial) you can change the serial settings to match your PTZ settings.
If using Axis Q7401 encoder, at it's front panel you have a TX/RX 485 port you can put you serial cable coming from you PTZ equipment. Check if PTZ is receiving serial RS422 or RS485 to match the encoder settings.
This encoder is a great choice to go from analog to IP.
Regards!