I looked around and first and found no answers. I just got a pair of M900 to do some 900mhz testing. There are 2 antenna ports on the top but no reference to them in the software. Can you use just one of these and terminate the other ? They are marked Chain0 & Chain1
Mike AE4ML
http://www.aredn.org/content/rocket-antenna-port-questions
Like all unused life RF connections it is recommended to terminate unused ports with a suitable dummyload/terminator to prevent RFI and reduce/prevent weather infiltration.