For my simple setup I've got 2 N210's each with an RFX2400 (using TX/RX for receive).
Are you sure you're really using TX/RX for receive? As the link Josh supplied says "The user may set the receive antenna to be TX/RX or RX2.
However, when using an RFX board in full-duplex mode,
the receive antenna will always be set to RX2, regardless of the settings."