Abstract: Apparatus, methods, and computer program products are disclosed for detecting or locating a viable data carrier in a downstream channel by a cable modem. When a cable modem is first installed by a cable operator or powered up by a user, it must first locate or tune in to the correct downstream channel in order to receive data from the headend of the cable plant. This time-consuming process can be shortened by performing two matches between the selected, potential downstream data carrier and constellation diagrams of certain modulation schemes. Through this method, potential channels for data carriers can be eliminated quickly by going through a “screening” process (the first constellation diagram match) thereby preventing those potential channels from going through a significantly more time-consuming second constellation match. The process begins with selecting a potential frequency channel from the downstream band.