Electronic measuring instruments
The electronic instrument used to analyze waves in the frequency domain is called a spectrum analyzer . Basically, it displays the energy distribution of a signal on its CRT screen. Here, the x-axis represents frequency and the y-axis represents amplitude.
Types of spectrum analyzers
We can classify spectrum analyzers into the following two types .
- Filter bank spectrum analyzer
- Superheterodyne spectrum analyzer
Now let's talk about these two spectrum analyzers one by one.
Filter Bank Spectrum Analyzer
The spectrum analyzer, used to analyze signals are of range AF is called filter bank spectrum analyzer, or real-time spectrum analyzer as it shows (displays) all variations of all input frequencies.
The following figure shows the block diagram of the filterbank spectrum analyzer.
The operation of the filterbank spectrum analyzer is mentioned below below.
It has a set of bandpass filters a nd each is designed to allow a specific frequency band. The output of each band pass filter is given to a corresponding detector.
All detector outputs are connected to the electronic switch. This switch allows the detectors to exit sequentially to the vertical deflection plate of the CRO. Thus, CRO displays the frequency spectrum of the AF signal on its CRT screen.
Superheterodyne Spectrum Analyzer
The spectrum analyzer, used to analyze the signals are of RF range is called superheterodyne spectrum analyzer . Its functional diagram is illustrated in the figure below.
The operation of the superheterodyne spectrum analyzer is carried outmentioned below.
The RF signal to be analyzed is applied to the input attenuator. If the signal amplitude is too large, it can be attenuated by an input attenuator .
The low pass filter (LPF) only allows frequency components that are below the cutoff frequency.
Mixer gets the inputs from the low pass filter and the voltage tuned oscillator. It produces an output, which is the difference in frequencies of the two signals applied to it.
The IF amplifier amplifies the intermediate frequency (IF) signal, that is, the output of the mixer. The amplified IF signal is applied to the detector.
The output of the detector is given to the vertical deflection plate of the CRO. Thus, CRO displays the frequency spectrum of the RF signal on its CRT screen.
So we can choose an s analyzerparticular spectrum low over the frequency range of the signal to be analyzed.