Acoustic spectrogram of the spoken Tokyo Japanese word minato

A spectrum analyzer or spectral analyzer is a device used to examine the spectral composition of some electrical, acoustic, or optical waveform. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids waveformogg|right|a sine square and sawtooth wave at 440 hz]] Waveform means the shape and form of a signal such as a Wave moving in a solid liquid or gaseous It may also measure the power spectrum. In Statistical signal processing and Physics, the spectral density, power spectral density ( PSD) or energy spectral density (

There are analog and digital spectrum analyzers:

• An analog spectrum analyzer uses either a variable band-pass filter whose mid-frequency is automatically tuned (shifted, swept) through the range of frequencies of which the spectrum is to be measured or a superheterodyne receiver where the local oscillator is swept through a range of frequencies. An analog computer (spelt analogue in British English is a form of Computer that uses continuous physical phenomena such as electrical mechanical A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for A band-pass filter is a device that passes frequencies within a certain range and rejects ( Attenuates frequencies outside that range In Electronics, the superheterodyne receiver (also known by its full name the supersonic heterodyne receiver, or by the abbreviated form superhet) is a A local oscillator is an electronic device used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer
• A digital spectrum analyzer computes the discrete Fourier transform (DFT), a mathematical process that transforms a waveform into the components of its frequency spectrum. In Mathematics, the discrete Fourier transform (DFT is one of the specific forms of Fourier analysis. Familiar concepts associated with a Frequency are colors musical notes radio/TV channels and even the regular rotation of the earth

Some spectrum analyzers (such as Tektronix's family of "real-time spectrum analyzers") use a hybrid technique where the incoming signal is first down-converted to a lower frequency using superheterodyne techniques and then analyzed using fast fourier transformation (FFT) techniques. Tektronix Inc is a North American company best known for its test and measurement equipment such as Oscilloscopes Logic analyzers, and video and mobile In Electronics, the superheterodyne receiver (also known by its full name the supersonic heterodyne receiver, or by the abbreviated form superhet) is a

Operation

A real time analysis of a song. This spectrum analyzer output features frequency on X (horizontal), magnitude on Y (vertical), and moves through time in sequence with the song

Usually, a spectrum analyzer displays a power spectrum over a given frequency range in real time, changing the display as the properties of the signal change. There is a trade-off between how quickly the display can be updated and the frequency resolution, which is for example relevant for distinguishing frequency components that are close together. With a digital spectrum analyzer, the frequency resolution is Δν = 1 / T, the inverse of the time T over which the waveform is measured and Fourier transformed. With an analog spectrum analyzer, it is dependent on the bandwidth setting of the bandpass filter. However, an analog spectrum analyzer will not produce meaningful results if the filter bandwidth (in Hz) is smaller than the square root of the sweep speed (in Hz/s), which means that an analog spectrum analyzer can never beat a digital one in terms of frequency resolution for a given acquisition time. Choosing a wider bandpass filter will improve the signal-to-noise ratio at the expense of a decreased frequency resolution. Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements

With Fourier transform analysis in a digital spectrum analyzer, it is necessary to sample the input signal with a sampling frequency ν_s that is at least twice the highest frequency that is present in the signal, due to the Nyquist limit. The Nyquist frequency, named after the Swedish-American engineer Harry Nyquist or the Nyquist–Shannon sampling theorem, is half the Sampling frequency A Fourier transform will then produce a spectrum containing all frequencies from zero to ν_s / 2. This can place considerable demands on the required analog-to-digital converter and processing power for the Fourier transform. An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic integrated circuit which converts continuous signals to Often, one is only interested in a narrow frequency range, for example between 88 and 108 MHz, which would require at least a sampling frequency of 216 MHz, not counting the low-pass anti-aliasing filter. In such cases, it can be more economic to first use a superheterodyne receiver to transform the signal to a lower range, such as 8 to 28 MHz, and then sample the signal at 56 MHz. This is how an analog-digital-hybrid spectrum analyzer works.

For use with very weak signals, a pre-amplifier can be used, although harmonic and intermodulation distortion may lead to the creation of new frequency components that were not present in the original signal. The total harmonic distortion, or THD, of a signal is a measurement of the Harmonic distortion present and is defined as the ratio of the sum of the powers Intermodulation or intermodulation distortion ( IMD) or intermod for short

Acoustic uses

In acoustics, a spectrograph converts a sound wave into a sound spectrogram. Acoustics is the interdisciplinary science that deals with the study of Sound, Ultrasound and Infrasound (all mechanical waves in gases liquids and solids Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies The spectrogram is the result of calculating the Frequency spectrum of Windowed frames of a compound signal. The first acoustic spectrograph was developed during World War II at Bell Telephone Laboratories, and was widely used in speech science, acoustic phonetics and audiology research, before eventually being superseded by digital signal processing techniques. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Speech-language pathology is the study of disorders that affect a person's Speech, Language, cognition voice swallowing ( Dysphagia) and the rehabilitative Acoustic phonetics is a subfield of Phonetics which deals with acoustic aspects of speech Sounds. Audiology (from Latin la ''audīre'' "to hear" and from Greek grc -λογία -logia) is the branch of Science that studies hearing Digital signal processing ( DSP) is concerned with the representation of the signals by a sequence of numbers or symbols and the processing of these signals Now spectrum analyzers cover the acoustic range.

RF uses

In telecommunications, for example, spectrum analyzers are used to determine occupied bandwidth and track interference sources. Cellplanners use this equipment to determine interference sources in the GSM/TETRA and UMTS technology.

See also

• Spectrometer
• electromagnetic spectrum
• Measuring receiver

External links

• Spectrum analyzer tutorial
• Spectrum analyser and general radio frequency eBooks
• Superheterodyne spectrum analyser simulator
• Spectrum analyser program for Linux
• Homebrew spectrum analyzer project
• Homebrew LCD spectrum analyser
• Sri Welaratna, "30 years of FFT Analyzers", Sound and Vibration (January 1997, 30th anniversary issue). A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies In Telecommunication, a measuring receiver or measurement receiver is a calibrated laboratory-grade Radio receiver designed to measure the characteristics A historical review of hardware spectrum-analyzer devices.

Manufacturer (alphabetic)

• Aaronia
• Agilent
• AirMagnet
• Anritsu
• Hameg
• Narda Safety Test Solution
• Rohde & Schwarz
• Standford Research Systems
• Tektronix
• Willtek