The Armstrong oscillator (also known as the Meissner oscillator) is an
electronic oscillator
An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating ...
circuit which uses an
inductor and capacitor to generate an oscillation. It is the earliest oscillator circuit, invented by US engineer
Edwin Armstrong
Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous awa ...
in 1912 and independently by Austrian engineer
Alexander Meissner
Alexander Meissner (in German: Alexander Meißner) (September 14, 1883 – January 3, 1958) was an Austrian engineer and physicist. He was born in Vienna and died in Berlin.
His field of interest was: antenna design, amplification and detectio ...
in 1913, and was used in the first vacuum tube
radio transmitters
In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
. It is sometimes called a tickler oscillator because its distinguishing feature is that the
feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
signal needed to produce oscillations is
magnetically coupled into the tank inductor in the input circuit by a "tickler coil" ''(L2, right)'' in the output circuit. Assuming the coupling is weak but sufficient to sustain oscillation, the oscillation frequency ''f'' is determined primarily by the
LC circuit
An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, and a capacitor, represented by the letter C, connected together. The circuit can a ...
(tank circuit L1 and C in the figure on the right) and is approximately given by
:
This circuit was widely used in the
regenerative radio receiver
A regenerative circuit is an amplifier circuit that employs positive feedback (also known as regeneration or reaction). Some of the output of the amplifying device is applied back to its input so as to add to the input signal, increasing the a ...
, popular until the 1940s. In that application, the input radio frequency signal from the antenna is magnetically coupled into the LC circuit by an additional winding, and the feedback is reduced with adjustable gain control in the feedback loop, so the circuit is just short of oscillation. The result is a narrow-band radio-frequency filter and amplifier. The non-linear characteristic of the transistor or tube also
demodulated the RF signal to produce the audio signal.
The circuit diagram shown is a modern implementation, using a
field-effect transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs co ...
as the amplifying element. Armstrong's original design used a triode
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as ...
.
In the Meissner variant, the LC resonant circuit is exchanged with the feedback coil, i.e., in the output path (vacuum tube plate, field-effect transistor drain, or bipolar transistor collector) of the amplifier (e.g., Grebennikov, Fig. 2.8).
Many publications, however, embrace both variants with either name. English speakers call it the "Armstrong oscillator", whereas German speakers call it the "Meißner oscillator".
See also
*
Opto-Electronic Oscillator
An opto-electronic oscillator (OEO) is an optoelectronic circuit that produces repetitive electronic sine wave and/or modulated optical continuous wave signals.
An opto-electronic oscillator is based on converting the continuous light energy fr ...
Footnotes
External links
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{{DEFAULTSORT:Armstrong Oscillator
Electronic oscillators