page_title: Ernst Ruhmer
section_title: Radiotelephone
hierarchical_section_title: Ernst Ruhmer / Career / Wireless telephony / Radiotelephone
caption_attribution_description: English: Photograph of Ernst Ruhmer radiotelephone transmitter circa 1905
context_page_description: Ernst Walter Ruhmer was a German physicist. He was best known for investigating practical applications making use of the light-sensitivity properties of selenium, which he employed in developing wireless telephony using line-of-sight optical transmissions, sound-on-film audio recording, and television transmissions over wires.
context_section_description: Ruhmer also carried out research in making audio transmissions using radio signals. In 1904, he was granted, along with Adolf Pieper, German patent 173,396, "A Process for Generating Permanently Undamped Electrical Oscillations", which described a method for creating "continuous wave" transmissions using a mercury-vapor vacuum-tube.
  In 1904 he developed a high-speed alternator which produced transmitting frequencies of up to 120,000 cycles-per-second. However, this effort never got beyond a basic prototype that generated less than .001 watt.
  Ruhmer also investigated radiotelephone transmissions using a high-frequency spark transmitter. This work took place during winter 1904-5, however, this approach had limited results, as he later noted that "the transmitted speech received on microphonic contact and telephone was rough and broken like that of a stammerer".
  In 1906, employing a design largely based on the hydrogen arc transmitter developed by Denmark's Valdemar Poulsen, he reported that he had constructed a transmitter capable of producing frequencies up to 300,000 cycles-per-second. Although the quality of the resulting audio transmissions were "strikingly good", and he felt that transmission range could be extended to several kilometers, these tests were only conducted over a distance of 500 meters.
  Ruhmer also investigated carrier current transmissions (then commonly known as "wired wireless"), where multiple radio signals are transmitted along an electrical conductor, which acts as a wave guide carrying the signals to designated locations. In 1911, it was reported that during a recent demonstration, "four transmissions—German, French, song and gramophone music respectively—were effected simultaneously, but the number can obviously be increased considerably without any disturbance".
  In 1907 Ruhmer wrote Drahtlose Telephonie, which was translated by James Erskine-Murray and published in 1908 as Wireless Telephony In Theory and Practice. This book reviewed the various technologies being investigated for wireless telephony, including both optical telephone research and the newer radiotelephone developments. Radio transmissions were soon recognized to be superior for most applications, as they were unaffected by weather, and were not limited to line-of-sight transmissions.
caption: Ruhmer's radiotelephone transmitter, circa 1905
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