Roof antennas and cameras came up a while back and now I have the diagrams to dig in a little further.

We'll use this photo by @tiltoncreative to help illustrate.
If you've ever wondered what all the things on the roof of a NASCAR Cup car do, here is a handy diagram.
More on how the roof camera decals work here: https://twitter.com/hoonable/status/1277640306356293638
Each of the pieces on the roof has a specific position of where it must be placed with reference points to the centerline of the car as well as the truck trailing arm crossmember below the car. The position of these is checked with a template during tech inspection.
You may remember the truck trailing arm crossmember from our discussion on skew. It is the bar that goes across the middle of the car where the truck trailing arms or "truck arms" for short mount. https://twitter.com/hoonable/status/1264953873929613312
This illustration shows a better view of where that truck trailing arm crossmember ends up on the car.
As I referenced in the aero thread yesterday, every piece on the car that touches the air is optimized for aero and that even includes the antennas on the roof. While they have a template for location, these antennas can be tilted to maximize airflow. https://twitter.com/hoonable/status/1288262007779663884
While small antennas may seem insignificant at first glance, every bit of air that can be controlled is another bit that can help with performance especially at aero dependant places like intermediate tracks so the small sharkfin antenna can be used to direct some air.
Parts available for the SMT system hint at this because there are dummy antennas specifically built for wind tunnel testing. https://twitter.com/hoonable/status/1277670640028471296
Every car is equal so everyone runs the same "camera" unit even if there is not an actual camera installed. Those that don't have a camera installed will have a dummy piece of equivalent weight. https://twitter.com/lilcal8/status/1288468929820622848?s=20
This is a great note on the camera and telemetry systems running standalone and not being hooked into the electrical system of the car. I did not know the specific type battery until now. https://twitter.com/Sfrymyer2/status/1288466516862808064?s=20
Some of the parts that teams are required to have in the car as part of that mounting solution that @Sfrymyer2 mentions above.
To clarify, the yellow part is the dummy weight and the mounting solution information is listed beside it in the diagram above. https://twitter.com/Sfrymyer2/status/1288471044840394753?s=20
The telemetry information is read from the ECU over CAN-BUS and the battery housing must be free and clear of any other pieces that teams install inside the car.
The following parameters are collected by the telemetry system.
All cars must have 3 "kits" from SMT installed to facilitate their equipment.
The "A-Kit" is a roof mount kit that costs around $100.

https://shop.sportvision.com/ProductDetails.asp?ProductCode=02%2D0767%2D00
The "B-Kit" is a set of claws that attaches to parts of the "A-Kit" to mount the vector unit. This set runs around $165.

https://shop.sportvision.com/ProductDetails.asp?ProductCode=02%2D0768%2D00
The "C-Kit" contains that battery housing as well as the CAN-BUS interface for the ECU that is mentioned above. It costs $610.

https://shop.sportvision.com/ProductDetails.asp?ProductCode=02%2D0769%2D01
A much better look at that unit. https://twitter.com/Sfrymyer2/status/1288473272707948546?s=20
SMT also sells a template for the roof.

https://shop.sportvision.com/ProductDetails.asp?ProductCode=06%2D0816%2D00
Teams find room for improvement everywhere, even doing slight position changes in antennas and it all adds up in the end. Hopefully thr separate antennas also help to explain why someone can be having radio troubles but still have a clear camera feed. https://twitter.com/xfinityracing/status/1274466669318950912?s=21 https://twitter.com/xfinityracing/status/1274466669318950912
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