I am designing a circuit board which will have multiple XBee modules on it. I will be using the RF Pad version of these modules, where the RF signal comes out on a pin of the device. The RF signal from each of the XBee modules will go to an RF splitter/combiner, the summing port of which will go to the antenna. I notice that the RF ground signal on these modules is electrically connected (internally) to the other ground pins of the module. To avoid ground loops and other problems, the RF (analog) ground and digital grounds should only be connected in one place. If I was designing the board with only one module, I would isolate the RF ground from the digital ground on my circuit board. This brings me to my question: for my circuit board with multiple XBee modules connecting to a common RF splitter/combiner, should I connect the RF ground signals of the modules together (and then to the ground of the splitter/combiner)? This will create a ground loop. If I only connect the RF ground of one module to the RF S/C, then the RF ground return for the other modules would be through the digital ground signal, through the other XBee module to its RF ground, to the RF S/C ground. Please let me know what you recommend.
although I’m not a hardware engineer I did find this comment on grounding (pg. 15):
http://ftp1.digi.com/support/documentation/90000976_P.pdf