Mark,

Sorry I was a bit late as I was back in the hospital for most of this week.

I'm not as familiar with XBee as I am with the lower frequencies subject to FCC Part 15 Regulations but I believe it will be a better fit for what you want to do.

1. It's pre-approved by the FCC. Getting Part 15 approval can cost several thousands of dollars. There's a loophole for "homebuilt" designs but your application sounds too commercial to fit the loophole.

2. There's much more spectrum and frequency hopping is automagically included so I suspect you can meet your desired schedule. If not, since they are all transceivers, you can do a query/response schedule from a master unit which will be simpler to manage than random transmissions from multiple transmitters.

Good luck and keep us updated - this is likely to interest many others.