ELECTRONIC MEASUREMENT AND INSTRUMENT: WAVE ANALYZER

ELECTRONIC MEASUREMENT
AND INSTRUMENT (2141002)
“WAVE ANALYZER”
BY
SHIVANGI SINGH

 The electronic instrument used to analyze waves is called wave
analyzer. It is also called signal analyzer, since the terms signal
and wave can be interchangeably used frequently.
 We can represent the periodic signal as sum of the following two
terms.
 DC component
 Series of sinusoidal harmonics
 So, analyzation of a periodic signal is analyzation of the
harmonics components presents in it.

 Basic wave analyzer mainly consists of three blocks − the primary
detector, full wave rectifier, and PMMC galvanometer.

The function of each block present in basic wave analyzer is
mentioned below.
 Primary Detector − It consists of an LC circuit. We can adjust the
values of inductor, L and capacitor, C in such a way that it allows only
the desired harmonic frequency component that is to be measured.
 Full Wave Rectifier − It converts the AC input into a DC output.
 PMMC Galvanometer − It shows the peak value of the signal, which
is obtained at the output of Full wave rectifier.

 This basic wave analyzer can be used for analyzing each and
every harmonic frequency component of a periodic signal.

Wave analyzers can be classified into the following two types.
Frequency Selective Wave Analyzer
Super-heterodyne Wave Analyzer

The wave analyzer, used for analyzing the signals are of AF range is called
frequency selective wave analyzer.
 Frequency selective wave analyzer consists 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 input
attenuator. If the signal amplitude is too large, then it can be attenuated by input
attenuator.
 Driver Amplifier − It amplifies the received signal whenever 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 & all these are cascaded with each other. We can vary the
capacitance values for changing the range of frequencies in powers of 10.
Similarly, we can vary the resistance values in order to change the
frequency within a selected range.
 Meter Range Attenuator − It gets the selected AF signal as an input &
produces an attenuated output, whenever required.

 Output Amplifier − It amplifies the selected AF signal if
necessary.
 Output Buffer − It is used to provide the selected AF signal to
output devices.
 Meter Circuit − It displays the reading of selected AF signal. We
can choose the meter reading in volt range or decibel range.

 The wave analyzer, used to analyze the signals of RF range is called
superheterodyne wave analyzer.
 The working of superheterodyne wave analyzer is mentioned below.
 The RF signal, which is to be analyzed is applied to the input attenuator.
If the signal amplitude is too large, then it can be attenuated by input
attenuator.
 Untuned amplifier amplifies the RF signal whenever necessary and it is
applied to first mixer.

 The frequency ranges of RF signal & output of Local oscillator are 0-
18 MHz & 30-48 MHz respectively. So, first mixer produces an
output, which has frequency of 30 MHz. This is the difference of
frequencies of the two signals that are applied to it.
 IF amplifier amplifies the Intermediate Frequency (IF) signal, i.e. the
output of first mixer. The amplified IF signal is applied to second
mixer.
 The frequencies of amplified IF signal & output of Crystal oscillator
are same and equal to 30MHz. So, the second mixer produces an
output, which has frequency of 0 Hz. This is the difference of
frequencies of the two signals that are applied to it.

 The cut off frequency of Active Low Pass Filter (LPF) is chosen
as 1500 Hz. Hence, this filter allows the output signal of second
mixer.
 Meter Circuit displays the reading of RF signal. We can choose
the meter reading in volt range or decibel range.
 The operating frequency range of this instrument is from 10 kHz
to 18 MHz in 18 overlapping bands selected by the frequency
range control of the local oscillator.
 The bandwidth is controlled by an active filter and can be
selected at 200, 1000, and 3000 Hz.

1. Electrical measurements
2. Sound measurements
3. Vibration measurements.

 https://www.tutorialspoint.com/electronic_measuring_i
nstruments/electronic_measuring_instruments_wave_
analyzers.htm
 Electronic Measurements and Instrumentation, by K.
Lal Kishore, Pearson India publication

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