Once you have the schematics, you will need a workbench and one each of the following items: The shack does not appear on the map, but is at the base of the hill the Array is built on.
You can find a set on a table near a workbench in a red abandoned tent, directly west of the entrance to SatCom Array NN-03d.Lucky Harith, the weapon specialized caravan merchant, sells a set of schematics.You can also kill Vance to obtain his Shishkebab (it is fully functional but very degraded). One set of schematics can be obtained from Vance at the end of the Blood Ties questline.As with all non-explosive custom weapons, possessing multiple copies of the schematics increases the initial condition of the weapon – one copy gives a condition equal to 75% of a character's Repair skill, two gets 100%, and three gets 125%.
