Xbee modules with bad range

Hi there,

I use a system with several Xbee-Pro modules.
A “transmitter” is reading the 8 digital inputs and is sending this information to several “receivers” that react on the info with setting outputs. Just I/O.
The “receivers” are located in the field, approx. 100 meters away from the “transmitter”, however, the system does not work. Between both TX and RX is a large stack of soil / ground.

Is it possible, to let all modules send the information if received further to the other receivers? Just to make sure the information gets everywhere.

If we use 9dbi antenna’s on all modules, is it usefull to put a 20 dbi antenna on the transmitter? Or ar the modules communicating in both directions all the time.

Please let me know any suggestions.

Best regards, Rinie