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Cryptophone
Mechanical voice scrambler · 1919 - this page is a stub

Cryptophone 1 was one of the first practical implementations of a voice scrambler for telephone, invented and patented in 1919 by the French Engineer Jules Carpentier 2 [1] and Eugène Poirson. The device uses inversion of the frequency spectrum by means of a motor-driven commutator.

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Jules Carpentier (30 August 1851 - 30 June 1921) was a former student of the prestigious École Polytechnique, the school for polytechnic engineering in Palaiseau, a suburb of Paris (France) [5]. In 1878 he bought the Ruhmkorff workshops in Paris, and turned it into a successful business for building electrical and magnetical devices [1]. Over the years, Carpentier patented a large number of inventions, mainly in the field of photography, cinematography (film) and telegraphy (telex).

  1. This name is uncertain and was propably not registered, but we assume it to be correct, as it was referred to as kryptofon, Kryptophon and kryptofoon in Polish, German and Dutch news articles of 1919 and 1920, in which the invention was announced [3][4]. Cryptophone would have been the French and English spelling.
  2. In publications of 1919 [3] and 1929 [4], his name is erroneously spelled as Charpentier. This is a common mistake and is often seen as an alternative spelling for the same name. Furthermore, he was a polytechnic engineer, not a physicist as suggested in the articles.

Thanks to Frank Dörenberg for bringing this device to our attention [7].
Patent   FR522916
In February 1919, Carpentier filed a patent for a for a secure telephony device, in which a motor-driven commutator is used to reverse the current of an audio signal 3340 times per second [4]. This technique, also known as chopping, introduces sidebands in the frequency spectrum – one of which is reversed – and is basically the mechanical equivalent of the diode-based electronic ring mixer. The reversing of the audio frequency spectrum is also known as voice inversion [6].

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The above drawing from French Patent 522916 [2] illustrates the chopping of the speech signal, which is subsequently sent over the telephone line. At the remote end of the line, an identical commutator running at the same speed (3340 Hz) — effectively another mixer — is used to make the signal legible again. For this to work properly, it is important that the commutators at both ends are synchronised. In the patent, Carpentier shows a number of possible solutions for this.

The invention was announced internationally, such as in Poland in July 1919 [3] and in Germany and the Netherlands in February 1920 [4], but it is unlikely that it became a successfully product, as Jules Carpentier unexpectedly died in a car accident the following year, on 30 June 1921 [1].

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Patent
  • French Patent FR522916
    Principe et procédés pour assurer l'etablissement de conversation téléphoniques scrètes et dispositifs électriques en permettant la mise en oevre pratique.
    Jules Carpentier and Eugene Poirson, 8 February 1919. 1
  1. Filed: 8 February 1919. Granted 8 April 1921. Published 9 August 1921.

References
  1. Wikipedia, Jules Carpentier
    Retrieved 24 May 2020.

  2. French Patent FR522916, ...conversation téléphoniques scrètes...
    Jules Carpentier and Eugene Poirson, 8 February 1919.

  3. Joanna (redactor), Announcement of Kryptofon in Poland
    Ilustrowany Kuryer Codzienny, 24 July 1919.

  4. Jan Corver, De kryptofoon
    Radio Nieuws, Volume 2, 1 February 1920. Page 45.
    File obtained from NVHR via this link.

  5. Wikipedia, École Polytechnique
    Retrieved 24 May 2020.

  6. Wikipedia, Voice inversion
    Retrieved 24 May 2020.

  7. Frank Dörenberg, Personal correspondence
    Received May 2020.
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© Crypto Museum. Created: Monday 25 May 2020. Last changed: Friday, 03 July 2020 - 12:00 CET.
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