A wireless client device discovers vacant DTV channels using location information acquired from a Dynamic Host Configuration Protocol server. The basic device is a two-terminal unit, denoted as a Signal Canceling Unit, which sensesthe signal available at its terminals, and applies negative feedback in order to cancel and absorb the signal. The sterically regulated methacrylic polymer comprises 50 to 100 mol-% unit based on methacrylate having a tertiary amino group bound to at least two aromatic rings in a side chain, wherein the number-average molecular weight is 5000 to 2000000, the poly dispersity coefficient is 1 to 1.