Hello everyone, I am Rose. Today I will introduce spectrum analyzer to you. A spectrum analyzer is a tool for analyzing the structure of electrical signals' spectrum. Signal distortion, modulation, spectral purity, frequency stability, and intermodulation distortion are all measured using it.

Ⅰ.  What is spectrum analyzer?

A spectrum analyzer  is a tool for analyzing the structure of electrical signals' spectrum. Signal distortion, modulation, spectral purity, frequency stability, and intermodulation distortion are all measured using it. Certain circuit systems, such as amplifiers and filter  s, can be measured using it. A meter is an electrical measuring equipment that can be used for a variety of purposes. It's also known as a frequency domain oscilloscope, a tracking oscilloscope, an analysis oscilloscope  , a harmonic analyzer, a frequency characteristic analyzer, or a Fourier analyzer, among other names. Modern spectrum analyzer  s can evaluate electrical signals in all radio frequency bands, from very low frequency to sub-millimeter wave bands below 1 Hz, and can display analysis results in analog or digital formats. It contains storing and calculating features if digital circuits and microprocessors are utilized inside the instrument; equipped with standard interfaces, it is simple to create an automatic test system.

Ⅱ.  What's the classification of spectrum analyzer?

There are two types of spectrum analyzer  s: real-time analysis and sweep frequency analysis. The former can gather all necessary spectrum information, analyze it, and display the results in real time when the measured signal happens, but the latter takes numerous sampling procedures to complete repeated information processing. The real-time spectrum analyzer  is mostly utilized for signal analysis that is non-repetitive and has a short duration. The non-real-time spectrum analyzer  is primarily used to examine a specific segment of continuous radio frequency transmissions and periodic signals ranging from audio frequency to sub-millimeter wave.

Sweep frequency spectrum analyzer 

It's a sweeping frequency superheterodyne receiver  with a display device that's mostly used to analyze the spectrum of continuous and periodic signals. It operates in the audio to sub-millimeter wave frequency range and only shows the amplitude of the signal, not the phase. The local oscillator uses a sweeping frequency oscillator  , the output signal and each frequency component in the signal under test go through difference frequency conversion in the mixer in order, and the resultant intermediate frequency signal goes through a narrowband filter,  It is added to the video amplifier as the oscilloscope's vertical deflection signal after amplification and detection, so that the vertical display on the screen is proportionate to the amplitude of each frequency component. The sawtooth voltage created by the sawtooth wave sweep generator controls the frequency sweep of the local oscillator. The horizontal sweep of the oscilloscope is similarly based on the sawtooth wave voltage, therefore the horizontal display on the screen is proportionate to the frequency.

Real-time  spectrum analyzer 

The instrument that extracts all of the signal's spectrum information for analysis and displays the result within the measured signal's limited time is primarily used to analyze non-repetitive stable random processes and short-duration transient processes, and it can also analyze frequencies below 40 MHz. Continuous signals with low and extremely low frequencies can show amplitude and phase. A real-time spectrum analyzer  is the Fourier analyzer. Its primary working idea is to use an analog-to-digital conversion circuit to transform the examined analog signal into a digital signal, which is then added to the digital filter  for Fourier analysis; it is controlled by the central processing unit. The quadrature digital local oscillator generates a digital local oscillator signal that changes according to the sine and cosine laws, and it's also used in Fourier analysis with the digital filter  and measured signal. A sweeping frequency oscillator  is the quadrature digital local oscillator. It will output when its frequency matches the frequency of the detected signal. The analysis result is obtained for the oscilloscope to display the spectrum graph after integration processing. The outcome of analyzing a quadrature local oscillator using sine and cosine signals is complex, but it can be translated to amplitude and phase. The results of the study can also be delivered to a plotter for printing or connected to a computer via a standard interface.

Ⅲ.  The working principle of a spectrum analyzer

The spectrum analyzer's primary function is to determine the spectrum content of the signal that is input into it. The spectrum analyzer.  for example, will measure the spectral content of the output filter  in the frequency domain if we wish to measure the output of a filter.  such as a low-pass  filter ,  It will also measure the noise content and display it in the CRO during this procedure.

A spectrum analyzer's job is essentially to generate vertical and horizontal scans on a cathode-ray oscilloscope, as indicated in the block diagram. The horizontal scan of the signal under test will be proportional to its frequency, whereas the vertical scan will be proportional to its amplitude, as we know.

The signal at the radio frequency level is fed into the input attenuator, which attenuates the signal at the radio frequency level in order to provide a horizontal sweep of the signal under test. To reduce any ripple components in the signal, the attenuator's output is routed to a low-pass filter,  It is then supplied into an amplifier, which boosts the signal's amplitude to a specified level.

It is also combined with the output of an oscillator adjusted to a specific frequency during the procedure. The oscillator aids in the generation of the feedback waveform's alternating nature. The signal is sent to the level detector, which translates the signal into the frequency domain after it has been combined with the oscillator and amplified. The amount of spectrum in a signal is expressed in the frequency domain in a spectrum analyzer, 

For vertical scanning, amplitude is required. To obtain the amplitude, the signal is passed to a voltage-tuned oscillator. At the radio frequency level, the voltage tuned oscillator is tuned. An oscillator circuit is typically constructed using a mix of resistors and capacitors. An RC oscillator is what this is called. The signal is phase altered by 360 degrees at the oscillator level. RC circuits of various levels are employed to achieve this phase shift. We usually have three levels.

For phase shifting, transformers are sometimes employed. A ramp generator can also be used to regulate the frequency of the oscillator in most circumstances. To acquire the pulse's ramp, the ramp generator is sometimes coupled to a pulse width modulator. The oscillator's output is routed into the vertical scanning circuit. On a cathode ray oscilloscope, it provides amplitude.

Ⅳ.  What’s the function of spectrum analyzer?

The spectrum analysis system's primary role is to display the frequency domain spectrum properties of the incoming signal. Real-Time Spectrum Analyzers and Sweep-Tuned Spectrum Analyzers are the two most common types of spectrum analyzers, depending on the signal processing methods used. The real-time frequency analyzer has the same functions as the real-time frequency analyzer. Display the signal amplitude in the frequency domain in real time. Its basic idea is that different frequency signals have corresponding filter  s and detectors, and the signals are subsequently transferred to CRT or liquid crystal display devices via a synchronized multiplex scanner. It has the benefit of being able to illustrate the instantaneous reaction of Periodic Random Waves (Periodic Random Waves)

Ⅴ.  What’s the character of spectrum analyzer?

The disadvantage is that it is costly, and the bandwidth range, number of filter  s, and maximum switching time are all limited (Switching Time). The most popular  spectrum analyzer is a scanning tuning spectrum analyzer.  which has a superheterodyne-like basic construction. The input signal is delivered directly to the mixer through the attenuator, and the oscillation frequency is generated linearly with time through the scan generator synchronized with the CRT by the adjustable local oscillator. After the signal is mixed and down-converted, the intermediate frequency signal (IF) is amplified,  filter ed, detected, and delivered to the CRT's vertical direction board, where the vertical axis displays the corresponding relationship between the signal amplitude and frequency. For the discrimination and measuring of signals of various frequencies, a lower RBW is unquestionably beneficial. When the signal is shown, a lower RBW will filter  out higher frequency signal components, resulting in distortion. The set RBW is directly related to the distortion value. RBW will very likely impair the identification of low-intensity signals by increasing the noise floor value (Noise Floor), reducing measurement sensitivity, and increasing the noise floor value (Noise Floor). As a result, the correct usage of spectrum analysis is the proper RBW width. Instrument is a crucial idea.

It is not commonly used by maintenance employees. For starters, the cost is more, and the procedure is more difficult. It's necessary to work with a signal generator. However, it is quite useful for locating flaws.

Ⅵ.  Where can we use spectrum analyzer?

Measurement of amplifier gain, frequency response and passive component characteristics

In cable television or communication systems, a vast number of passive components like as amplifiers and taps, connectors, and coaxial cables are employed. Because the quality of the components has a significant impact on the signal's characteristics, pre-screening aids in ensuring signal quality. The frequency response characteristics of the equipment under test are evaluated using the tracking generator of the spectrum analyzer (DUT). The plotter (Plotter) can be used to obtain textual data from the measurement result.

Communication monitoring

Wireless communication must use high frequency due to spectrum usage rules. The antenna transmits and receives signals. Using a spectrum analyzer and an antenna, it is simple to determine the strength of the present transmission signal and the carrier frequency. The signal source's frequency, amount, and amplitude are displayed on the screen. If a directional antenna is utilized, it goes without saying that the two pieces of measurement equipment will be able to determine the area of the signal source. This is also the primary detection method employed by relevant units to prevent unauthorized radio wave transmission (such as illegal radio stations, etc.).

Cable TV image information measurement

Cable television (CATV) is a project that uses cable to send video to the subscriber's house (such as coaxial cable or optical cable). Due to technological advancements, it has been recommended to open up microwave The function of transmission or satellite transmission to subscribers' houses in the form of Spot in order to reduce the difficulty of excavating roads and burying cables while also lowering prices. At the moment, Warner Pictures has launched satellites with 150 video channels to serve customers in the Northern California area. Video is obviously sent by cables, microwaves, and satellites. It has coexisted to serve the public, providing viewers with a wider range of options.