Use the following as a guide for trouble shooting.
Section 1: Includes antenna systems by vehicle.
Section 2: Includes radio antenna system diagnosis procedures for AM/FM concerns using internal radio diagnostics.
Section 3: Includes antenna lead diagnosis.
Perceived reception issues may be a result of environmental factors.
Reception may be diminished in certain areas due to power wires, buildings and/or overpasses.
Aftermarket window tint may interfere with reception.
In cases that are questionable, locate identical vehicle and verify concern (if the like vehicle is same, condition may be normal).
For more detail see Repair Manual Group 91- Communication of the vehicle you are working on.