rheslip blogged about his simple scalar network analyzer project:
The principle is to stimulate an electrical network with a sinewave and measure the magnitude of the response. If we sweep over a range of frequencies and measure the power transmitted through the network we can determine its frequency response. Transfer from the input port (1) to the output port (2) is called the network’s S12 S-parameter response. By using a return loss bridge or coupler we can measure the reflected power – the S11 response. A Vector Network Analyzer is a much more complex piece of gear that measures the phase response of the network as well.
In practical terms, a Scalar Network Analyzer allows you to test and characterize crystal filters, attenuators, highpass/lowpass/bandpass filters, cable losses, and antennas among other things. Its also useful as a signal generator and the power detector can be used on its own for power measurements.
Check out the video after the break.