The WW2 Navy aircraft GP-7 transmitter had TUs to provide continuous coverage 350 to 9050 kc. The ground/shipboard version of this rig (I forget the nomenclature) used the same TUs. Later (1950s), the Navy SRT-14,15 and16 transmitters covered 300 kc to 26 mc continously. (In 10 cps steps!) Dennis D. W7QHO Glendale, CA