Select appropriate source to proceed with AC analysis. Place an appropriate source to proceed with AC analysis. Several are in the library tech_ngspice: drag from Explorer to place in schematic. For the rest: in the side-bar select Component tab, then schematic technology, and click an entry on the Spice component-menu (this is an electric built-in library named spicepartsS3), then click to place it in the schematic. Double-cilck the instance to edit properties. Here we used VSRC.ic from library tech_ngspice.
Make sure voltage levels have proper values
AC analysis component is present in the tech_ngspice library as dotAC.ic. Drag it from side-bar Explorer to place in a schematic.
Double-click the instance to edit its properties.
Click the SIM button on toolbar to write ngspice netlist and run the simulation. Launch symprobe on the output rawfile via toolbar wave button.
See also: Reuse View Analog Simulation results in symprobe; for an AC-Analysis, the Trace menu offers an easy way to plot Phase, Magnitude, and db20.