An electronic instrument used to analyze waves is called a waveform analyzer. It is also called a signal analyzer because signal and wave can be used interchangeably.
We can represent the periodic signal as the sum of the following two terms.
- DC component.
- series of sinusoidal harmonics.
So, the analysis of a periodic signal is the analysis of its harmonics components.
It is also known as a signal analyzer or carrier frequency voltmeter or frequency-selective voltmeter or selective level voltmeter. This instrument uses a set of filters for tuning and a voltmeter to analyze the signal in the frequency domain. Waveform analyzers are available in the RF range (low) and 50 MHz below range and also run through the AF range with high-frequency resolution.
Basic Wave Analyzer
The basic wave analyzer mainly consists of three blocks – primary detector, full wave rectifier, and PMMC galvanometer. The block diagram of the waveform analyzer is shown in the figure below:
The function of each block of the basic wave analyzer is mentioned below:
- Primary Detector – It consists of an LC circuit. An inductor, L, and capacitor can adjust the values of C in such a way that it allows only the desired harmonic frequency component to be measured.
- Full Wave Rectifier – It converts AC input to DC output.
- PMMC Galvanometer – It shows the peak value of the signal, which is received at the output of a full wave rectifier.
By replacing each block with the corresponding component(s) in the above block diagram of the waveform analyzer, we will obtain the corresponding circuit diagram. So, the circuit diagram of the waveform analyzer will look as shown in the following figure –
This wave analyzer can be used for the analysis of each harmonic frequency component of a periodic signal.
Types of Wave Analyzers
Wave analyzers are classified into two types on the basis of the frequency range.
- Frequency Selective Wave Analyzer
- Superheterodyne Wave Analyzer
Frequency Selective Wave Analyzer
Frequency-selective waveform analyzer works on the principle of the frequency-selective voltmeter. It is tuned to a single signal frequency and at the same time rejects all other types of signal components. Such analyzers include a narrow passband filter section to tune the frequency.
This type of analyzer is mainly used in the measurement of the frequency range of audio which is 20Hz to 20 kHz. The frequency Selective Waveform Analyzer Block diagram is shown below which consists of different blocks.
A frequency-selective wave analyzer consists of a set of blocks. The function of each block is mentioned below:
- Input Attenuator – The AF signal, which is to be analyzed, is applied to the input attenuator. If the amplitude of the signal is too large, it can be attenuated by an input attenuator.
- Driver Amplifier – It amplifies the received signal when necessary.
- High Q-filter – It is used to select the desired frequency and reject unwanted frequencies. It consists of two RC sections and two filter amplifiers and all of them cascade with each other. To change the range of frequencies in powers of 10 one can change the capacitance values. Similarly, changing the frequency within a selected range can change the resistance values.
- Meter Range Attenuator – It receives the selected AF signal as input and generates an attenuated output whenever required.
- Output Amplifier – It amplifies the selected AF signal when necessary.
- Output Buffer – It is used to provide the selected AF signal to the output device.
- Meter Circuit – It displays the reading of the selected AF signal. Meter readings can be selected in the volt range or decibel range.
Superheterodyne Wave Analyzer
Superheterodyne wave analyzer works on the principle of mixing or heterodyning. Heterodyne input signal to be analyzed, i.e. mixing in high IF signal through the internal local oscillator. Oscillator tuning causes components of the signal frequency to move into the passband of the IF amplifier. This type of analyzer is mainly used in the measurement of the RF range.
The working of Superheterodyne wave analyzer:
- The RF signal to be analyzed is applied to the input attenuator. If the amplitude of the signal is too large, it can be attenuated by an input attenuator.
- The untune amplifier amplifies the RF signal as and when required, before applying it to the mixer.
- If the frequency range of the local oscillator’s RF signal and output is 0–18 MHz and 30–48 MHz, respectively, the first mixer produces an output with a frequency of 30 MHz. It is the difference in frequencies of two signals applied to it.
- The IF amplifier amplifies the intermediate frequency (IF) signal, i.e. the output of the first mixer is the amplified IF signal applied to the second mixer.
- The amplified IF signal of the crystal oscillator and the output frequencies are the same and equal to 30MHz, then the second mixer produces an output with a frequency of 0Hz. It is the difference in frequencies of the two signals applied to it.
- The cut-off frequency of the active low pass filter (LPF) is chosen as 1500 Hz. Therefore, this filter allows the output signal of another mixer.
- The meter circuit displays the reading of the RF signal. Meter readings can be obtained selectively in the volt range or decibel range.
Applications of Wave Analyzers
The applications of the waveform analyzer are demonstrated below:
- It measures the harmonic distortion of the signal.
- Used in electrical, vibration, and sound measurement.
- The signal energy can be measured using a well-defined BW.
- The harmonic distortion of the amplifier can be measured and each separate component can also be determined in the periodic signal.
- A waveform analyzer is applicable for electrical measurement.
- Using this analyzer, harmonics can be isolated as well as displayed.
- It is used as an automatic frequency controller.
- It is used to reduce vibration as well as the sound produced through machines used in electrical industries.
- Used to measure the amplitude of the preferred frequency component within a signal.
- Signal The desired frequency components can be selected to test the signal.
- It is used to measure noise as well as signal amplitude through interface signals.
- It is mainly used to analyze the DC component within a periodic signal.