AM/FM Radio

In my shop, I have an old AM/FM/8-track/turntable stereo from probably the '70s. I don't recall the brand name right now, but it was a good one back then. The problem is, it doesn't pick up a signal very well at all. I might be able to pick up my favorite station in AM or FM, and I might not. If I do get it, it may go away after a while. I think the problem is, what I have here is a pole-barn type building with a steel shell. I do have an external antenna connected, but it is just a piece of flat, two-conductor wire similar to the old TV lead-in that splits like a "T" and is fastened to one of the roof trusses. It is still inside the building. If I open one of the overhead doors (on the South side, toward most of the stations) sometimes it helps, but if I open the other one, it hurts!

  At the same time, I have a small portable radio from the same time period, with a 16-18" mast antenna, sitting in the East-facing window of my engine assembly room that works very well!

  I'm convinced that I need a better antenna in a better location for the "big" shop radio, but don't know what I need for an antenna or lead-in, or where it needs to go. Would an antenna mounted on the outside of the building, on the North side work, or would I need to mount it on the South side? The radio sits on a shelf on the North side of the shop, and it's 30 feet to the South side. Or would an antenna in the engine room window work, that's only 18-20 feet away?

  Do I need to just bite the bullet and go buy a newer stereo with newer technology, or would I have the same problem?    I have tried three different stereos, all from the '60s/'70s, with the same results. Move the portable to the shop? Naw, I have some decent speakers (yes, from the '70s) on the wall in the shop, and need to hear the Stereo effect when they play Led Zeppelin or Pink Floyd, or Jimi Hendrix.    

  So, radio geeks, what do you say? Thanks in advance.   BW