I recently spoke with a fellow who was trying to use his hotspot on a frequency around 438 MHz. He wasn’t having much luck and with good reason. The MMDVM firmware blocks usage on all frequencies between 435 and 438 MHz. The block was implemented because 435-438 MHz is a suband used by the amateur satellite service and some amateurs noticed an increase of terrestrial interference with satellite communications.
Another ham that I spoke to is using a hotspot frequency that is also the input of several coordinated repeaters in my area. This is also not a good idea as it can also create interference, especially when operating a hotspot while mobile.
Here is my list of recommended simplex hotspot frequencies that is not likely to cause interference to other operators, repeaters, or satellites:
Most hams seem to set the admit criteria on their radios to Always for use with simplex hotspots. I strongly recommend that you use Channel Free instead to reduce the possibility of doubling.
73 de K2IE