Abstract: A collapsible-helix antenna, continuously variable in length and self-resonant with a uniform resistance over an exceedingly wide frequency range, for example 2-32 mHz. The collapsible-helix is continuous in two sections: a fixed-length, shorted-out section wherein the turns of the helix are collapsed upon each other; and a variable-length section wherein the helix has an approximately constant pitch, and is a radiating element. Means are provided to drive turns of the helix from either section to the other, providing a helix with continuously variable physical and electrical length.