In addition,
The FCC rules are abundantly clear about who is permitted to add radios to a radio system. As an employee, volunteer, staff, friend, amateur radio operator, hobbyist, interested party, neighbor, random dude on the street, etc. you are not permitted to add any radios to the radio system without the permission of the licensee. You, as one of the above, do not have an FCC license to transmit on their frequencies. Only the licensee does, and that licensee is the only one authorized by the FCC to add additional radios to the system.
The licensee is responsible for all radios on their system, including those purchased by volunteers, staff, employees, etc. Simply being part of the department doesn't change that.
The rules go in depth about what can be programmed into the radios, where they can be used, and by whom they can be used.
Adding a radio to their system isn't OK without permission. Adding a cheap Chinese radio with horrible specifications just adds to the issue. I've had users put these Cheap Chinese Radios onto my systems and it's -really- easy to tell when it happens. The audio sounds like garbage. Not what you want in an emergency.
Here is what you need to do:
1. Find out who holds the FCC license for the radio system you use. You can find that using the FCC search page.
2. Talk to that person. Get permission, in writing, add your own radio the system. Make sure it's in writing and is specifically allowing you (as in your name) to add a specific number of radios their system. Keep that paper as proof.
3. Find out what kind of radio system they are using. Specifically frequencies, emission type, digital/analog, trunked, etc.
4. Ideally find out what specific model radio they purchase for the department.
4a. Get the exact same radio. It'll allow them to program the same file into your radio.
5. Find out if they or the dispatch center using any sort of individual radio ID'ing system (MDC1200, FleetSync, DTMF, etc)
5a. Get an ID assigned to your radio and have your radio programmed to send out that ID. Don't show up on their radio system without it.
It's not always as easy as buying a cheap radio off E-Bay or Amazon. There are a lot of variables you need to consider if you want it to work correctly. No point in buying a radio that isn't going to work on their system.
We are happy to assist you if you can find out some details. If your budget is tight, and they are not running trunked or digital, you can often find used/reconditioned quality radios for a decent price if you know who to ask.