The ornamental design for a portablekeyboard, as shown and described.
FIG. 1 is a front elevational view of the portable keyboard of the present invention held in a vertical position in a supporting base;
FIG. 2 is a rear elevational view of FIG. 1;
FIG. 3 is a left side elevational view of FIG. 1;
FIG. 4 is a right side elevational view of FIG. 1;
FIG. 5 is a top plan view of FIG. 1;
FIG. 6 is a bottom plan view of FIG. 1;
FIG. 7 is an exploded view thereof; the broken lines shown are for illustrative purposes only and form no part of the claimed design;
FIG. 8 is a front elevational view of the top portion of FIG. 7; and,
FIG. 9 is a rear elevational view of FIG. 8.
The broken line showing of a carrying strap secured to holding elements on the rear of the top portion in FIGS. 8 and 9 is for illustrative purposes only and forms no part of the claimed design.