I wasn't sure if it's needed or not. The diagram the instructions I linked above showed one, so I assumed I did. I noticed the N9TAX Slim Jim has a ferrite bead on it too, which made me think it was required.
I'll try it without first I think. Getting something up on the roof should really improve everything either way!
84 FJ60 The TuRDle
& '89 Pickup Ext Cab DLX 22RE/5spd