Hans,
No, there is no constitutionally defined measure of journalism. That is in one part why Connecticut no longer issues any press credentials, as well other states and jurisdictions have as well. They were unable to define who was and who was not a "legitimate" journalist.
For work, I now primarily cover Feds. I have some of my own radios, and not all of their channels are publicly listed , or defined as to what they frequency does, but I've had help there in some instances. I at times end up with 'their radios' from people I know to listen to those channels that I wouldn't be able to monitor with my own radios. I understand the need for encryption, in some instances, but overall I see it encrypting everything ... like DCFD's Fire & EMS dispatch ... as an egregious act of curtailing a public's right to know.
There are other issues with this move, such as Nassau County, NY, PD going to P25 Phase II Encrypted, which effectively cut off the ability of the volunteer fire & EMS department to monitor the police. In Nassau County the vollie FDs share the EMS duties with the NCPD's Emergency Ambulance Bureau, often speeding up their response times by getting the calls off the PD dispatch, which is critical for cardiac cases, MVAs and other situations. For not EMS purposes the FD often gets dispatched, and getting a jump on that is always beneficial.
Each department is issued 3 radios that can monitor the PD encryption ... sure 3 radios may sound good, but in the village I grew up in, with nearly 60,000 people, there are four engines, two trucks, a heavy rescue, two ambulances, three chiefs, operating from five separate houses ... so those three radios really do no good to the community in regard to speeding up response times.
There are countless incidents now where the FDs have had issues because they cannot monitor the NCPD EMS bus, because they operate on the precinct channels. In other situations there have been dispatch delays for an MVA where the PD were reporting a fire, but that info goes from cop to NCPD dispatch, who sends it to NC FireCom, who dispatches it, before the tones go out for for the vollies to head to the house, wait for a crew, and roll out. In the past you could end up with a vollie on scene with a fire extinguisher , or first responder on scene, beating the bus, beating the engine, which greatly enhances public safety.
But you can't hand an encrypted radio to every vollie in 76 departments across 9 Battalions ... but yea, there is no need for what is considered 'the public' by some jurisdictions to monitor the police.