An embodiment of the invention is a modular card style radio-signal modem suitable for wireless data communication to a personal computer. The modem comprises a main circuit board substrate defining an opening, a card-to-computer connection interface operably linked to the circuit board, a radio transceiver on the circuit board in communication with the connection interface. The radio transceiver has a receiver input and a transmitter output. The card modem also includes a dielectric block antenna duplexer attached to the circuit board and suspended in the opening, the duplexer having a transmit signal input in electric communication with the transmitter output, a receive signal output in electric communication with the receiver input and an antenna connection electrode.