Who really invented the Ultradyne?




The Ultradyne saga continues.......


Who really invented the ULTRADYNE?



The term "Ultradyne" was coined by R. E. Lacault in 1924 for his superheterodyne radio receivers which used the "Modulation System". Since then Ultradyne is also synonymous of a particular type of RF mixer for reception. Its originality lies in having used a triode not powering the plate with the usual DC voltage (+B) but with the radio frequency voltage of the local oscillator which employed another triode. This leads to a rhythmic interruption (marked by the LO) of the antenna RF signal on the plate that consequently produced the intermediate frequency which in Lacault’s receivers was around 115 kHz. In 1927/1928 the Ultradyne circuit was used up to 30MHz with excellent results, the problem was to build oscillators that worked well at that frequency and beyond! In truth this mixer was invented by R.A. Jouaust in 1921 to compensate for the low sensitivity of the mixers of the time that combined the RF signal with that of the local oscillator to obtain the IF by rectification. He, however, used it only in the "heterodyne" type of receivers albeit with a great outcome. Lacault had the merit of being the first in having adapted and used this circuit in a superheterodyne, to have improved it and made popular (at least in the twenties), but the story of the Ultradyne does not ends here.......

Recently looking on the Net at some other information for the Ultradyne I came across a German forum where it was stated that a circuit with the same principle was already invented and patented in Germany in 1920! This has caused me perplexity and amazement but also a lot of interest, so I started a search to find some more details and maybe a copy of the original patent. This task has not been easy but finally I succeeded. Here below you can see the original schematic diagram from the patent. The German title is the following:

“Einrichtung zum Empfang kontinuierlicher elektrischer Schwingungen” (Ref. 1)

Which translated, it sounds like this:

“System for receiving continuous electrical oscillations”


Patent 366546



From the diagram it is clear that the tube 3 is the mixer, where the winding 7 picks by induction, from the winding 6, the oscillating voltage from the oscillator thus feeding the anode of the mixer. The local oscillator signal is generated by the tube 4 and is amplified by that numbered 5. The beat is picked up in the terminals 8 and 9. The interesting fact is that in the text of the German patent the mixer 3 is described as a tube that serves as an amplifier and interrupter, this is, without question, a much better explanation than those of Jouaust and Lacault, and confirms what I have written on the actual working of the Ultradyne (Ref. 2). There is no doubt that already in 1920 the switching mixing system was in the air!

The patent application is dated August 10, 1920, then about 10 months earlier than that of Jouaust which is from June 22, 1921.

Sometimes it happens that the same (or similar) invention arises in the mind of some inventors in different times and places.





(Rev. A)
From a better translation of the original text of the Telefunken patent it argues that the circuit was designed to be used not solely for a shift of the antenna RF signal into the Audio band (Heterodyne) but also to a first conversion in the "Medium Frequency" and then in audio, therefore with the concept of the superheterodyne. Not only that, but to avoid "interferences" it was proposed to use the same type of circuit in several frequency conversions in cascade! The text of the patent shows another peculiarity; the function of the tube 5. This tube rather than amplify the oscillator signal turned it into impulses! The interrupter tube (3) plate received these short pulses through the coil 7. According to the inventor(s) that caused an amplification.





     1- Gesellschaft für drahtlose Telegraphie m.b.H. in Berlin (TELEFUNKEN) - Einrichtung zum Empfang kontinuierlicher elektrischer Schwingungen - Patent N° 366546 - January 6, 1923 (Patent application date: August 10, 1920)

     2- www.radiopharos.it - The Ultradyne dilemma






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1st Issue - November 2014
Revision A: Added Note 1
March 2015