Thanks Dave,
Will this one work? It appears to offer full duplex and is isolated, which help with all the RF floating around the site.

www.serialcomm.com/serial_rs232_converters/rs232_to_rs485_converters/externally_powered_rs232_to_4_wire_rs485_rs422_con verter/ext_rs232_to_4_wire_rs485_rs422.product_general_in fo.aspx

Thank you again.
Terry K9HA
Sneaky-geek