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
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
“Einrichtung zum Empfang kontinuierlicher elektrischer
Which translated, it sounds like this:
“System for receiving continuous electrical oscillations”
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.
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.
Gesellschaft für drahtlose Telegraphie m.b.H. in Berlin
- Einrichtung zum Empfang kontinuierlicher elektrischer
Patent N° 366546 -
January 6, 1923
(Patent application date: August 10, 1920)
The Ultradyne dilemma
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1st Issue - November 2014
Revision A: Added Note 1