Friday is the last day to apply for a federal coupon to purchase a digital converter box. The box is required to watch digital television signals broadcast over the air. The nation transitioned to digital broadcasting June 12, but households have until Friday to request the $40 converter box coupon. To apply for a coupon, call 888-DTV-2009 or visit www.dtv2009.gov before the program ends July 31. The coupons are valid for 90 days after they are issued.