Yep, it just screws off. Although the stem is attached to the car, and can't be removed easily. It affects AM radio noticeably, and affects FM slightly but it's not noticeable (it's one of the 3 FM antennas).
This is mine:
This is where I got it:
http://www.amazon.com/gp/product/B00...ms_ohs_product
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[Current] Tesla Model 3 Performance
[Retired] Audi R8 V10 6MT, BMW i3 BEV, BMW i3 REx, BMW Z4 sDrive35i DCT, BMW 335i Coupe 6MT