Large metal shop, is there anyway to put a pass through antenna.

I was thinking that the inside antenna would not connect via wireless to any radio but would be able to use any radio and maybe the signal would come through the outside antenna to the inside antenna then any radio could get reception wireless.

I’m not sure what ideas you have, but the idea is to mount an antenna OUTSIDE, use a coaxial cable and connect it to one inside radio. There’s not enough signal in that 1 cable to act as a mini-broadcast station once indoors.

What you might be able to do is connect an FM transmitter in the shop to some internet radio source, as a for instance, but it would be 1 channel at a time, not a broad-band FM amplifier.

https://amzn.to/4b7l14s

If we are talking about multiple listeners for multiple stations, you are going to be better off setting up Wifi inside the shop, and letting them use personal devices with Blutooth speakers.