= Frequency modulation laboratory
The New Jersey Institute of Technology's \i[Lab 2: FM Modulation, Demodulation and Bessel Zeros], Part I, prepares a <voltage-controlled oscillator> in low-frequency mode. A <frequency counter> reads its output while a buffered constant <electric potential difference> calibrates its sensitivity. Sweeping the control voltage checks <linearity>; the calibrated gain is then held fixed.<Lab 2: FM Modulation, Demodulation and Bessel Zeros, NJIT ECE 489>[Part I, Figure 2 and steps T1–T7: VCO preparation, frequency-counter readout, DC sensitivity and linearity sweep]{ref}
An audio oscillator replaces the constant control voltage. An <oscilloscope> displays the <signal> and its <FFT> <frequency spectrum> together. Zero modulation supplies a carrier reference. Increasing message <amplitude> reveals sidebands, compares their heights with the carrier, and locates a carrier minimum. These readouts test the spectrum and infer <frequency deviation>. This is a student procedure, not a report of measured results.<Lab 2: FM Modulation, Demodulation and Bessel Zeros, NJIT ECE 489>[“The FM Spectrum”, steps T8–T13: audio-oscillator input, simultaneous waveform/FFT, unmodulated reference, relative sideband heights and carrier minimum]{ref}
A carrier minimum is a minimum of one <Fourier coefficient>, not disappearance of the whole <signal>. In the ideal model the first positive zero of $J_0$ is approximately $\beta=2.4048256$, while the <wave envelope> remains $A$. The lab's introductory special-cases paragraph agrees with this rounded value; step T12 mistakenly repeats the equal-sideband value for the carrier zero.<Lab 2: FM Modulation, Demodulation and Bessel Zeros, NJIT ECE 489>[“Special Cases, β=1.45 and β=2.405”, compared with the inconsistent numerical annotation in T12]{ref}
The interpretation also has practical limits. A finite recording limits <frequency> resolution; inadequate sampling can cause <aliasing>; and nonlinear VCO response can introduce extra components. Keeping the gain fixed and first checking <linearity> helps distinguish those effects from a change in <FM modulation index>. The diagrams above are independent model calculations, not laboratory measurements.
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