Frequency Modulation

Frequency Modulation Definition

Modulation is the process by which information is encoded from a message source in order to optimize it for transmission. Frequency Modulation (FM) is the encoding of information in a carrier wave by changing the instantaneous frequency of the wave. FM technology is widely used in the fields of computing, telecommunications, and signal processing.

Diagram shows the difference between the waves of a modulating and carrier signal, and frequency modulation.

What is Frequency Modulation?

Frequency Modulation is a modulation in which the frequency of the carrier wave is altered in accordance with the instantaneous amplitude of the modulating signal, keeping phase and amplitude constant. Modification of carrier wave frequency is performed for the purpose of sending data or information over small distances. 

Frequency Modulation index is consistently over 1, requires high bandwidth in the range of 200 kHz, operates in a very high frequency range of 88 to 108 Megahertz, has a complex circuit with an infinite number of side bands, and receives a high quality signal with high sound quality. Frequency and phase modulation are complementary principal methods of angle modulation, which is a class of carrier frequency modulation often used in telecommunications transmission systems.

FM signals can be generated either by using direct frequency modulation, which is achieved by inputting a message directly into a voltage-controlled oscillator, or by using indirect frequency modulation, which is achieved by integrating a message signal to generate a phase-modulated signal, which is then used to modulate a crystal-controlled oscillator, the result of which is transmitted through a frequency multiplier to produce an FM signal.

Frequency Modulation use cases include FM radio broadcasting, magnetic tape-recording systems, monitoring newborns for seizures via EEG, radar, seismic prospecting, sound synthesis, telemetry, two-way radio systems, and video-transmission systems.

Frequency Modulation equation: FM: VFM (t) = Vco sin (2 p [fc + (Df/Vmo) Vm (t) ] t + f)

Amplitude Modulation vs Frequency Modulation

Amplitude Modulation (AM) is a modulation in which the amplitude of the carrier wave is altered in accordance with the instantaneous amplitude of the modulating signal, keeping phase and frequency constant. Modification of carrier wave amplitude is performed for the purpose of sending data or information over long distances.

Amplitude Modulation index ranges from 0 to 1, requires low bandwidth in the range of 10 kHz, operates in medium and high frequency ranges of 535 to 1705 Kilohertz, has a simple circuit with only two side bands, and receives low quality signals with poor sound quality.

FM and AM function in the same manner, however the manner in which their carrier waves are modulated differs. With AM, the strength of the signal varies in order to incorporate sound information. With FM, the frequency at which the current changes direction per second for the carrier signal is varied in order to incorporate sound information.

Frequency Modulation in Communication Systems

There are two different types of frequency modulation used in telecommunications: analog frequency modulation and digital frequency modulation.

In analog modulation, a continuously varying sine carrier wave modulates the data signal. The three defining properties of a carrier wave -- frequency, amplitude, and phase -- are used to create AM, PM, and Phase Modulation. Digital modulation, categorized as either Frequency Shift Key, Amplitude Shift Key, or Phase Shift Key, functions similarly to analog, however where analog modulation is typically used for AM, FM, and short-wave broadcasting, digital modulation involves transmission of binary signals (0 and 1).

Frequency Modulation in Vibration Analysis

Vibration analysis is a process for measuring and analyzing the levels and patterns of vibration signals or frequencies of machinery in order to detect abnormal vibration events and evaluate the overall health of machines and their components. Vibration analysis is especially useful with rotating machinery, in which exist fault mechanisms that may cause amplitude and frequency modulation abnormalities. The demodulation process can directly detect these modulation frequencies and is used to recover the information content from the modulated carrier wave.

How Does OmniSci Help Monitor Frequency Modulation?

In many telecommunications networks, it is necessary to implement modulation in order for information-bearing signals to be represented by a waveform that can effectively pass through a transmission medium. This modulated signal is then reverted to the original information-bearing signal via demodulation. Disruption of this transmission may occur if there are abnormalities in  the modulated signals.

Detecting signal anomalies or abnormal vibration patterns within enormous volumes of data signals is not possible using traditional solutions. Using OmniSci, telco analysts can easily detect and visualize network signal anomalies from billions of rows of records, with point-and-click SQL queries returned in milliseconds.