Abstract: This describes a method for improved data signaling equipment for use with well-drilling tools for rapidly sending measurements made down the hole in the wellbore to the surface without the need of an electric cable. A special well tool is connected into a drill string having a drill bit coupled thereto for drilling a borehole. During normal drilling operations, the data-sending equipment is not in operation, and the main body of circulating or drilling fluid is passed through a main valve in the downhole tool and bypasses a pressure-changing unit. A sensing unit is incorporated in the downhole tool and measures downhole parameters. When it is desired to send these data to the surface, the main circulation of drilling fluid is stopped and the bypass valve closed. Then, a small amount of fluid is supplied to the "closed" drill string from a substantially constant-pressure source.