Frequency Modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency.
It was very efficient and better than its predecessor Amplitude Modulation (AM), in which the amplitude of the carrier is varied, to convey information, while its frequency remains constant.
There were many patent disputes related to the invention of FM, but as is clear now Edwin. H. Armstrong is considered the father of FM.
Excellent articles on the life of Edwin H Armstrong and the invention of FM can be found in [1] and [2].
One of the earliest research papers on frequency modulation by Edwin Armstrong is 'A Method of Reducing Disturbances in Radio SignalingBy a System of Frequency Modulation' Published in Proceedings of the IRE, Volume 24, Issue 5, May 1936 Page(s):689 - 740.
One of the earliest patents disclosing frequency modulation is Patent number: US1941066 by Edwin H. Armstrong, Filing date: Jul 30th 1930, Issue date: Dec 26th 1933
It relates to a method of reception in signalling systems based on frequency modulation.
There are many other patents covering FM, such as Patent number: US2323698 by Edwin H. Armstrong, Filing date: Oct 12th 1940, Issue date: Jul 6th 1943, disclosing phase shifting method for generating frequency modulated signal.
However, US1941066 is the earliest patent identified which discloses Frequency Modulation.
It relates to a method of reception in signalling systems based on frequency modulation.
There are many other patents covering FM, such as Patent number: US2323698 by Edwin H. Armstrong, Filing date: Oct 12th 1940, Issue date: Jul 6th 1943, disclosing phase shifting method for generating frequency modulated signal.
However, US1941066 is the earliest patent identified which discloses Frequency Modulation.
Hence, we can consider US1941066 as the basic/ foundation/ original patent or the first patent of Frequency Modulation (FM).
The story of Edwin H Armstrong is very inspiring, I encourage you to read up on it from the sources in the references.
Remember this man whenever you tune in to any FM radio station.
References:
[1] http://www.yonkershistory.org/arms.html
[2] http://www.ee.columbia.edu/misc-pages/armstrong_main.html?mode=interactive
[3] http://users.erols.com/oldradio/
[4] http://www.nndb.com/people/133/000099833/
[3] http://users.erols.com/oldradio/
[4] http://www.nndb.com/people/133/000099833/