OP25 can capture data from a hardware device to a sample file. These can be analyzed later or used for debugging etc..
User-collected digital samples are available [http://op25.osmocom.org/p25-samples here] but - be warned - these files can be quite large.
To use a sample file with OP25 you'll need both the .bz2 and .info files. The .bz2 will need to be uncompressed (using "bunzip") before OP25 recognizes it.