xbee s1 with sparkfun regulated board not sending data from pixhawk

I am using Xbee s1 , with SparkFun XBee Explorer Regulated,
I tested the peer to peer communication between two Xbees , mounted on usb explorer board, and they work just fine tx and rx both way.

then I tested one with 3,3 v i\o fdti cable connected to the xbee on the regulated board, and it works just fine (communicate with the one on the usb explorer board)

then I connected the ftdi directly to the pixhawk uart , and tested that I get data from it. ( again , works just fine)

but when I switch between the ftdi cable to the xbee on the regulated board, it sends nothing !!!
I was able to verify that the pixhawk do revive the data coming from the Xbee on the usb explorer board.

so what can be the problem???

What baud rate does your device run at?

Have you set the XBee to match the baud rate of the device?

Does the Pixhawk operate at 3V or 5V?