Q: Is there a distance limitation when using DMR on UHF?
- It seems there might be a distance limitation of maximum 45 mi.

A: Yes, there is a range limit on DMR.
Here is one test.
www.va3xpr.net/search-range-limit-dmr/

But we have actually broken that two-way (portable) record out to 110 miles (mobile).
Mt. Washington to Malden, MA on VHF DMR.

There are other factors like terrain obstructions, antenna gains and radio power levels.

Separately, we have confirmed One-Way reception of a DMR repeater over 200 miles (Grand Manaan Is., New Brunswick to Shapleigh, ME).
- This was during a summertime tropo enhancement over water.

73,
Bill, NE1B