Chapter 9 Exercise: Designing and Building a Low-pass Filter

spectrum analyzer connected to a current probe around the center of an unconnected wire

Students design and build a low-pass filter. Then evaluate it to see how well it performs.

Preparation:  Students will be given a set of design parameters that their filter should meet. For example, "greater than 20 dB attenuation from 30 to 200 MHz." They should have a preliminary design in mind before coming into the lab.

Equipment Required:

  • Vector Network Analyzer
  • Cables and adapters
  • Copper tape, utility knives, soldering iron
  • Filter component kit including:
    • copper-clad board to build the filter on
    • board-edge connectors
    • filter components such as capacitors, inductors and/or ferrites with various values

Procedure:

Step 1: Students design a filter to meet the specified requirements before coming into the lab.

Step 2: Use the utility knife to cut away unwanted copper on one side of the board to form traces and solder pads.

Step 3: Solder the board-edge connectors and components to the board. 

Step 4: Measure the insertion loss from 10 MHz to 3 GHz.

Step 5: Repeat the steps above if necessary to meet the requirements.  

Step 6: Submit a report showing the design, design calculations, and the general approach used to ensure that the filter would work at high frequencies.   

Notes: 

A sample lab exercise is provided here - Filter-Design-Lab020.pdf

This could also be a student design competition.