Does the car antenna NEED to be mounting outside the car

I have installed quite a few and it does work best outside but I have not had any complaints from customers when mounted inside the vehicle. Put it on the front dash or rear shelf of the car pointed up. the metal on the roof and being mounted upside down could block reception.

I have both Sirius and XM, and the antennae are inside the car back beneath the back window- reception in the L.A. area is fine for both. There are occasional dropouts in heavy tree-lined areas and under some freeway overpasses, but for the most part- especially within range of the terrestrial repeaters- throwing the antennae face up in the back window works for me. But I'd imagine that the dropouts will be fewer with the antenna on the roof or trunk lid.

I hope not because I've had mine in the back window for 2 years

I have one in my Miata that has a hardtop (just fiberglass though) and just unzipped the passenger seat and put it at the top of the headrest and zipped it back up.

Outside is best.

It will and can work inside the car, but the antenna was designed to be placed outside the vehicle and ideally mounted on the roof and with a five inch ground plane (metal) around it.

Again, this is "ideal" and I got this data from talking to RF antenna engineers who make this their living.

The only problem I have is I don't trust people. I'm always afraid that someone is going to clip the antenna off "just because" it's there for the taking.

We are in the bay area and drive through the tree laden hills to and from work with the Sirius antenna in the middle of the front dash which works like a champ. Some drop outs in Redwood areas. I use a XM Pioneer Airware without a external antenna with the unit on the dash works great too but better of course with an external antenna. We do get a stronger signal with Sirius and fewer drop outs as their birds are more directly overhead in our local.

So try it inside what do you have to loose?

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For what its worth: I have a Jeep Wrangler with a fiberglass "hard" top. I noticed ZERO signal degredation from moving the antenna into the Jeep and on top of my roll cage (steel). Previously, having the wire out my passenger door and out onto my hood near the cowl just resulted in paint scratches.

And cd quality?? pfff... I've learned to live without it on Sirius!