The present invention relates a bidirectional signal transmission apparatus and method, wherein said apparatus comprises a processor unit connected in signal communication with an Ethernet, an RF modulation/demodulation unit, and an RF frequency conversion unit connected in signal communication with a coaxial cable network. The data signal input from the Ethernet is modulated into standard IEEE802.11 signal by means of said signal processing unit and RF modulation/demodulation unit, and then down-converted from 2.4 GHz or 5.8 GHz standard IEEE802.11 signal to a range of 500 MHz to 2000 MHz, and preferably to a range of 900 MHz to 1200 MHz. The bidirectional transmission apparatus further includes a frequency band selector for selecting different frequency bands so as to broaden the bandwidth of the signal and a real broad band data transmission is accomplished.