M Radio", Johns Hopkins Univ Press, 2010
     I am apparently unfair to Mr Carson; Armstrong quoted him out of context, and I did not dig up
     the original paper.

Gagliardi, "Introduction to Communications Engineering", Wiley Interscience, 1978.

Gray and Mathews, "A Treatise on Bessel Functions and Their Applications to Physics", MacMillan and Co, 1895.

Klapper, "Selected Papers on Frequency Modulation", Dover 1970. (Out of print, but available
     via used book markets such as abebooks or amazon &md