Hartley oscillator

Hartley oscillator

The Hartley oscillator is an LC electronic oscillator that derives its feedback from a tapped coil in parallel with a capacitor (the "tank circuit"). Although there is no requirement for there to be mutual coupling between the two coil segments, the circuit is usually implemented as such. A Hartley oscillator is essentially any configuration that uses a pair of series-connected coils and a single capacitor (see Colpitts oscillator for the equivalent oscillator using "two" capacitors and "one" coil). It was invented by Ralph Hartley, who filed for a patent on June 1, 1915 and was awarded patent number [http://patimg2.uspto.gov/.piw?Docid=01356763&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D1,356,763.PN.%2526OS%3DPN%2F1,356,763%2526RS%3DPN%2F1,356,763&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page] 1,356,763 on October 26, 1920.


Hartley oscillators may be series or shunt fed.A Hartley oscillator is made up of the following:

* Two inductors which need not be mutual (may be a two-winding transformer)
* One tuning capacitor

Advantages of the Hartley oscillator include:

* The frequency is varied using a variable capacitor
* The output amplitude remains constant over the frequency range
* The feedback ratio of the tapped inductor remains constant

Disadvantages include:

* Harmonic-rich content of the output
* It is not suitable for a pure sine wave


The Hartley oscillator was extensively used on all broadcast bands including the FM 88-108MHz band. An example is given of the Scott 310E RF oscillator for its FM section.


The Hartley oscillator was invented by Ralph V.L. Hartley while he was working for the Research Laboratory of the Western Electric Company. Hartley invented the design while overseeing Bell System's transatlantic radiotelephone tests of 1915. In 1946 Hartley was awarded the IRE medal of honor "For his early work on oscillating circuits employing triode tubes and likewise for his early recognition and clear exposition of the fundamental relationship between the total amount of information which may be transmitted over a transmission system of limited band-width and the time required." [Ralph V. L. Hartley, Legacies, IEEE History Center, updated January 23 2003, [http://www.ieee.org/organizations/history_center/legacies/hartley.html] ] (The second half of the citation refers to Hartley's work in information theory which largely paralleled Harry Nyquist.)

See also

* Armstrong oscillator
* Colpitts oscillator
* Clapp oscillator
* Vačkář oscillator
* Opto-Electronic Oscillator


* Radiotron Designer's Handbook, 4th edition

External links

* [http://www.tpub.com/content/neets/14181/css/14181_81.htm Hartley oscillator] , Integrated Publishing

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