진공관
The use of Morse code somewhat limited the usability of these broadcasts, as it required farmers to learn how to translate the telegraphic dots-and-dashes. Vacuum tube transmitters, capable of audio transmissions, had recently been developed, and in early 1917 Terry began making test transmissions using the new technology. For one of these tests he hosted a gathering at his home to listen to a transmission of phonograph records, although at the time the guests were generally unimpressed with hearing music that could just as easily be played on a nearby record player. But because vacuum tube technology was still in the experimental stage, 9XM did not introduce regular audio broadcasts at this time.