Olce's Brain Dumpster

Frequency modulated -> delta amplitude of X(t) gives delta frequency in X'(t)

Objective:

15khz FM transmitter in small form factor, preferably capable of 5 watts. Tunable around standard commercial FM ranges, adjacent amateur ranges or similar.

Maximum deviation: ?? 75khz commercial, 5 khz in LMRS

The maximum frequency deviation of the carrier is usually specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz

https://www.fcc.gov/narrowbanding-overview

Ideally tunable and in workable range, no high SWR.