Old magnetic cell phone antenna-UPDATE

He said the booster works great in the shop. with (one assumes) a modern proper band antenna...

So the booster is tuned to 4g or perhaps 3g where as the old antenna is 1st Generation/analog

Yes a non-resonate antenna will work and you can even make it work fairly well. I do it often. but the proper antenna will blow it away 9 times out of 8

I tried an old antenna that I had and did not have real good results so I broke down got a new magnetic antenna and 15' up in the air, my signal goes from 1 bar to 5 bars. Now I just take the repeater out of my shop and use it in the fiver

that booster is also tuned for the old frequencies,

The reason that I asked is that I have a booster in my shop which works great and is easy to get to and take out. For kicks and giggles I took it to my 5th wheel and hooked it up using a steel plate on the roof as a ground plane and an old ('90s vintage) magnetic antenna left over from the old bag phone days. It barely got me one more bar on my phone. I am taking a chance and ordering a new Wilson magnetic antenna of the right frequency. If it works-problem solved. If not, it certainly will not be the last $20 that I have wasted. I figured the distance between the indoor and outdoor antennas is not quite the issue with a magnetic one vs. a yagi antenna like I have on my shop

Without doing a ton of research I'd say NO. Depending on the design it might work.. But odds are very high it will not.. Dutch explained why.

This is why your Over the Air TV antenna still works. they did not change frequencies. they still use the same channels.. just the carrier and display channels are no longer locked together.

It's not the technology that's an issue, but the frequencies it's tuned for. There have been a number of fairly widespread new frequencies or "bands" added for cell use over the years, and the older antennas often not work well with all of them. That means how well it works will be dependent on which bands are in use where you are at the time.