Frequency Modulation Simulator
In Frequency Modulation, the frequency of the carrier signal varies in accordance with the message signal's amplitude. See Mathematical Background=>
Change the parameter values to see the effect.
Frequency deviation
ฮf = ฮฒ × fm
sFM(t) = Ac cos(ฯct + kf∫m(t)dt)
where ฯ = 2ฯf & kf = Frequency Sensitivity
Modulation index, ฮฒ = (kf * Am) / fm
๐งช Experiment for Students:
"Changing carrier amplitude affects only the displayed signal magnitude and transmitted power. It does not change the frequency deviation, modulation index, or bandwidth of an ideal FM signal. In another simulator, set the Message Amplitude to 1 and Frequency Sensitivity ($k_f$) to 5. Observe how the wave 'stretches' and 'squeezes'. Next, increase the Message Amplitude to 2.5. Notice that the frequency swings become much wider because the peak frequency deviation ($\Delta f = k_f \cdot A_m$) has increased."
Understanding Frequency Modulation (FM) Performance
Modulation Index ($\beta$)
The FM modulation index ($\beta$) is defined as the ratio of peak frequency deviation to the message frequency. Unlike Amplitude Modulation (AM), the modulation index in FM can be significantly greater than 1. A small value ($\beta < 1$) corresponds to Narrowband FM (NBFM), while larger values produce Wideband FM (WBFM).
Bandwidth and Carson's Rule
An FM signal theoretically contains an infinite number of sidebands. In practice, the required transmission bandwidth is estimated using Carson's Rule: $BW \approx 2(\Delta f + f_m)$. Therefore, FM bandwidth depends on both the peak frequency deviation ($\Delta f$) and the highest modulating frequency ($f_m$).
Noise Immunity
Frequency Modulation offers excellent resistance to noise compared with AM. Because information is carried by frequency variations rather than amplitude changes, FM receivers can use limiter circuits to suppress amplitude-based noise and interference while preserving the original information.