In California, the relevant organization is NARCC. Any time that you set up a new repeater, you should ideally go to them and follow their policies to get your repeater into a state of "coordinated" so you can fall under their protection from future interference. Unfortunately, when it comes to high density urban areas like the bay area, we are essentially out of free repeater pairs, so unsurprisingly the politics involved in getting a new repeater on the air is eye-watering for "just" a hobby.
While I do work on a few permanent repeater systems coordinated under NARCC, I'm not the formal trustee for any of them, so I have relatively little interaction with the coordination committee. Where I do often end up being the trustee is for temporary repeaters which are deployed for only a matter of days for special events such as the Wildflower Triathlon or the Bay Area Maker Faire. Getting coordination for these events wouldn't work out, since the coordination process is so slow and labor intensive, so I often get challenged by other amateurs for "how dare I set up a repeater without NARCC coordination."
When it comes to UHF repeaters, I actually kind of do technically have NARCC coordination. At least in the 440 band, NARCC was kind enough to set aside one of the repeater pairs to be designated as a "test" pair. This pair is designated as a free-for-all, and presumably meant primarily for use at new repeater sites for evaluating range to assist in getting a new repeater coordinated. I've been having great success using it for these small weekend deployments in much the same way that you would select a simplex frequency for an event and just pray that no one else needs the frequency.
At least in California, the best pair to use for temporary or portable repeaters is:
I didn't know about this pair until last year when I stumbled upon it in a band plan graphic on the NARCC and the Santa Clara County websites.
Unfortunately, it doesn't seem that there is a likewise allocation on any of the other repeater bands, which is understandable since 2m repeater pairs are in such greater demand than UHF pairs (at least a longer waiting list beyond there being none left?). I know of some groups who will just pick a repeater pair that's not locally used much and try and fly it in under the radar, but if I were to ever need a 2m pair for a temporary deployment, I plan to follow essentially the same protocol I use for utilizing an existing repeater, only for just their frequency pair instead of their actual machine:
- Identify a repeater within the area where I need communications resources.
- Reach out to them before the event to seek permission to use their repeater pair.
- Set up a repeater on their pair with a different PL tone. Possibly have them disable their box for the hours of operation.
- Thank them profusely after the event
- Nudge the hosting organization to donate $100-$750 to the repeater trustee for the use of their repeater pair and dealing with us for the weekend.
Many repeater trustees take the coordination process very seriously, and it's a relatively tight-knit community of repeater operators across California, so you will make a bad impression on a lot of people very quickly if you get known for setting up random repeaters on other people's repeater pairs, even if just for a special event.