I've recently become quite fascinated (again) by early tech, and in digging around the World Radio History site have been able to learn a good deal more about things that were only hinted at in publications available to me in the past. Although the subject is more general radio interest, arc technology was typically operated below 500 kHz, Hence placement of this posting here in the LW category. The use of arcs to generate "continuous waves" is rather interesting, more so where advances were made in telephony. A nice account of this, from 1918 is "Radio Telephony" Alfred N. Goldsmith. It contains a discussion of many examples of equipment and experiments by Poulsen and others, and can be found here.
worldradiohistory.com/BOOKSHELF-ARH/Bookshelf_Early_Radio_Technology.htm
It has me wondering about making some very curious experiments with batteries and pencil leads, large coils etc.. The idea of some manner of "Transmitter" involving no conventional electronics and 100+ year old methods has quite captured my interest.