Back when I had my Veloster, I was working on a radio comms system for a local car club. I hadn't made much progress by the time I crashed it; the setup we had at that point was just Baofeng UV-5R walkie talkies hooked up to Nagoya UT72 magnetic antennas to get some actual range... and the leader & I were the only ones who actually had them as I didn't consider the setup finished yet. With my Veloster and his Dodge Ram we could run the antenna cables out the doors as they were tough enough to still work while jammed in a car door. His Hellcat that he's trying to fix has frameless door glass, however, and now that I have a Mini, I do too, which complicates this arrangement.

An idea I had was modifying a stock sharkfin to fit an extra antenna, then run an extended antenna cable through the existing hole. If successful this would allow mounting an antenna for vehicle-to-vehicle comms without having to cut an extra hole in the roof. The problem is, I don't know how "dense" the stock sharkfin is i.e. how much of its volume is actually taken up by important stuff, and I don't want to cut up my existing unit to see, nor do I want to waste money on another one if the whole operation is just not possible. Has anyone ever cut one of these in half lengthwise to see what was inside it?

(If I was doing this whole setup over again, I'd probably try CB radios, but the club leader states he's already tried that before and got even less range than our Baofeng setup somehow, and no, we're not using illegal power levels with our radios so I have no idea how that happened.)

 

You may want to rethink that option - getting the sharkfin antenna off and on the car is "interesting" (my video shows the easiest method, but be prepared for lots of muttering while trying to do the task). There's honestly not a whole lot of room inside my antenna (the large base variety), and I suppose a lot less in the "small base" version. Seems like it would be easy enough to use a magnetic mount antenna - just run it out the hatch if you don't want to run it out a frameless window (not quite sure why that would be a problem - sounds more like an opportunity to me).

 

I wasn't the one who originally saw a problem with the frameless glass, that was the crew leader's idea. Likely (and understandably) he fears that shutting the door on an antenna cable might break the glass. Leaving the windows down is not an option because of Alaska's climate & weather for most of the year. As for running it out the hatch, this might create issues with the cable interfering with the operation of the vehicle. I planned to eventually use lapel mics which would enable the radio to be kept out of the way, but never got that far. Also, this isn't just about my car, I'm trying to create a solution that can be used on a wide variety of cars. We've got notchbacks (like the aforementioned leader's Hellcat) and wagons/large SUVs (Durango, leader's old Magnum) in our group, which would make that solution more difficult.

And running wires outside the cabin to external mag mounts just looks and is janky. It worked as a temporary solution for testing range & reception, but on a permanent basis, it's ugly. What I'm trying to come up with here is a permanent, visually discreet mounting solution that can be used by a wide variety of cars without cutting extra holes in the roof or otherwise doing permanent damage.

 

The last thing I'd worry about is breaking window glass with a small coax antenna, but it is a little fiddly, and if you don't like the look of a mag mount antenna, you're going to have to get creative.

I've seen antenna mounts the clip to the edge of a trunk, which could be used on the edge of the hood, running the coax through the firewall. That's about as clean as you're going to get, and there's actually a ground connection to the hood / trunk lid, which is good from a radio wave propagation standpoint (as compared to a mag mount).

There are also through-glass antenna mounts I've seen - maybe that would work through the sunroof glass?

Anyway, you can get a feel for the lay of the land watching my video (forgot to attach it to my previous post), both in getting access to that area, and what the "innards" of the large-base antenna look like, too...

 

FWIW, here's a photo I just took of the "cap" and the circuit board. There doesn't really appear to be any logical point of access for a cable to go through that board, but I haven't taken it off the base to see if the other side might provide a clue to an "inert point" that could be exploited for a feed-through...

 

Alternative, do you use the FM antenna? Maybe gut it & repurpose for the purpose of the OP?