The codecs and narrow frequencies used on most public safety trunked radio networks is truly terrible. IMBE and AMBE+2 should have never made it past Y2K, yet Motorola and Project 25 have ensured these remain in widespread use on these networks: https://en.wikipedia.org/wiki/Project_25

If Whisper achieves 85% or higher accuracy on this audio, it would be a miracle. Garbage in, garbage out tbh. Project 25 needs to move to a modern codec, ideally not one seeing little development done by one small company.