Sending GPS data over XBEE RF link problem

I have two XBEE-PRO XSC(S3B) units interfaced through the Sparkfun Explorer USB interface boards. If I plug these into two PCs and run XCTU in terminal mode, they talk to each other just fine. My application is to have an RS232 GPS module (4800/8/n/1) feed data to one XBEE and have it appear at the other (only one way communication).
So, for now the receiving end is the same XBEE talking to XCTU.
The transmit end is a bit messier. The RS232 GPS feeds an FTDI-based serial to USB converter which then feeds the transmitting XBEE. Both the GPS and the Sparkfun are powered by an independent 5v supply since there’s no USB host to supply power. The GPS has an LED indicator that lights steady until it acquires satellites, then blinks once/second. That’s happening. If I plug the output of the FTDI converter directly into the PC’s USB port and run a simple terminal program, I see the GPS data. But when I plug the same into the transmitting XBEE, I get nothing. Thinking that this might be similar to the null modem issue from the old RS232 days, I got a USB OTG (OnTheGo) adapter cable. That also gives me no results. Any suggestions as what to try next is appreciated.

I think your problem here is that both the Sparkfun XBEE module and the serial to USB converter are USB devices, and neither is a USB host. A valid USB setup consists of a single host (typically your PC) and then one or more devices which the host can control and communicate with. Communication is then only ever Host <-> Device, never Device <-> Device.

The correct way to do this is connect the RS232 output from the GPS directly to the XBEE through a RS232 to TTL level converter. So just using a pure serial connection, no USB involved.

Your USB OTG cable will not help here. It’s only for “intelligent” equipment which knows how to be both a USB device and a host. That doesn’t apply to either of the USB devices you have here.