I’m on a team at a startup who are using 900MHz XBee SX and XBee Pro SX modules for as part of a project. The XBee SX modules have been working flawlessly, but many of the Pro SX modules have failed with shorted antenna connectors.
I believe it is caused by an impedance mismatch on the antenna. The reflected signal causes the driver or receiver in the XBee to fail with a short to ground. I can confirm this with a simple ohm meter test on the antenna socket. All of the modules that can communicate have an open circuit reading, and all that can’t communicate read short circuit.
I’m not able to find any references online to this fault. I thought it was me doing something wrong until we ordered an mPCIe to XBee board with a Pro SX pre installed. It had failed too, and the manufacturer got back saying the rest of his stock had failed in the same way. They had tested them without antennas connected.
We have had several of our products fail because of this issue as well.
I’m reaching out here because I want to know if anyone else has experienced this problem, and if Digi are aware of it.
No, Digi is not aware of this as I am not aware of anyone else reporting it. Also all XBee modules are tested as part of the manufacturing process for two way communications and making sure they meet specifications. If they do not, then they do not pass the test and are removed from the production line. Only modules that pass this testing get a label as the final part of the process.
I’ve submitted a ticket to Digi regarding the issue, but for anyone else who has the same problem, these are my findings. We’ve got multiple XBee PRO SX and XBee SX antenna connection failures. It’s not just the PRO SX modules that I originally thought.
I ran an experiment to try and kill both an SX and PRO SX module. A 900MHz antenna was connected to each module with a 10cm U.FL to SMA cable. I was unable to damage the modules by removing the U.FL connector on the module itself while it was polling, but I was able to damage the XBee SX module by removing the antenna from the SMA connector during polling. I suspect the fault only occurs coincidentally when the impedance changes during a transmission, caused by reflections in the short cable. I believe the PRO SX module could be destroyed through the same method, but I’m not willing to sacrifice another module.