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Scopy Network Analyzer

Introduction

For you to switch to this instrument, click on the “Network Analyzer” from the menu list as illustrated. The small white squares allows you to run/stop the instrument without having that instrument in the current display.

Front Panel

1. Run/Stop Button

Starts and stops the capture of Network Analyzer Instrument. Alternatively, the capture can be started and stopped by clicking on the small white square at the right of the instrument on the left side menu.

2. Settings Menu Button

Shows or hides the general settings menu.

1. Reference Channel

Sets the reference channel for the network analyzer from the oscilloscope probes 1+ and 2+ to act as the phase reference.

2. Frequency Sweep Settings

Logarithmic/Linear – Sets the type of scale for the frequency axis.
Min and Max Frequency – Sets the minimum and Maximum Frequency to be displayed in the Bode plot. The minimum frequency ranges from 1 mHz to 20kHz and the maximum frequency ranges from 1mHz to 20MHz.
Samples Count – Sets the number of samples for each measurement from 10 to 10000

3. Waveform Settings Settings

Allows the user to change the amplitude and offset of the generated signal. The amplitude can be set to any value within the range of 1uV to 10 V. The offset value can be changes from -5 V to 5 V.

4. Display Settings

Allows you to adjust the view of the displays whether in Bode, Nyquist, or Nichols plot. By default, as you switch to this instrument, the minimum/maximum magnitude is set to -90 dB/10dB, but this can be set to any value within the range of -120 dB to 120 dB. The minimum/maximum phase value is set to -180/180 degrees by default but this can be changed to any value within -180 to 180 degrees. You can adjust these values before, during or after you click run. This is for viewing the plot effectively.

2. General Settings Menu Button

Shows or hides the control menu. Export button let's you export the network analyzer data.

1. Plot

You can choose what plot to be displayed in the plot area ( Bode, Nichols or Nyquist )

2. Export button

4. Cursors button

Shows or hides the cursors on Bode plot. When enabled, the cursors will show, and you can move them on plot by dragging the left\right arrow controls. The cursors indicate the frequency, the magnitude/phase and also the Δmagnitude and Δphase.

5. Plot area

Plots

Bode Plot

Bode Plot shows the Frequency response of a system in two parts, one part is the Bode magnitude plot that contains magnitude expressed in dB across the frequencies set from the control menu and the Bode phase plot expressing the phase shift.

Bode plot display may be modified from the available configurations in Frequency Sweep Settings and Display Settings from the Control menu.

Zooming the display

After capturing the signal, the graph may be zoomed in on the desired location by holding and dragging on the minimum and maximum desired of the frequency like shown below. This will zoom in both the Bode magnitude plot and Bode phase plot. To zoom in or out on magnitude or phase, use display controls from settings panel.

The default view that is set from the control menu may be returned by clicking the right-mouse button.

Nyquist Plot

Scopy network analyzer also features another way of showing the frequency response of a system, it is through the Nyquist diagram. Nyquist diagram is a polar plot of the frequency response that displays the amplitude in dB and phase angle on a single plot to determine if the system is stable or unstable. Display Settings control the Nyquist diagram by adjusting the minimum and maximum magnitude to the desired value.

To zoom in or out, you can use the + and - buttons (See above image). When zoomed in, you can hold left click and drag the plot around.

Nichols Plot

Nichols plot is another method of picturing frequency responses of systems. As you can see in the illustration, the Nichols plot shows the gain magnitude on a logarithmic scale (dB) in the y-axis and the phase on linear scale (degrees) in the x-axis. You can determine the gain and phase margins graphically and easily using this plot. The gain margin can be graphically determined by getting the absolute value of the magnitude axis intersect. The phase margin is determined by the distance between the origin and the phase axis intersect. The settings you applied to the controls when plotting either in bode or Nyquist will also reflect in the Nichols plot.

Network Analyzer - Low Pass Filter Example

In the following example we will show how to use the Network Analyzer to obtain the frequency response of a low pass filter circuit.

Consider the circuit in the figure below:

Oscilloscope Positive Channel 1 ('+1') is used as reference channel, connected at the input of the filter along with the Waveform Generator channel 1 ('W1'). Oscilloscope Positive Channel 2 ('+2') is connected at the ouput of the filter.

The oscilloscope negative input channels are connected to ground.

Breadboard connections for such a circuit are displayed below:

In the Network Analyzer interface, set the Reference: Channel 1 and the frequency range: Min Freq 1kHz and Max Freq 10MHz.

Run the instrument. The resulted plot is the frequency response of the low pass filter for the component values chosen.

The signal's amplitude is attenuated for frequencies larger then the cutoff frequency.

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Scopy Network Analyzer

Introduction