FIG. 1 is a front perspective view of an ornamental design for a portable digital radio according to the present invention;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a top view thereof.