Foster-Seeley Discriminator: Advantages and Disadvantages

This page explores the advantages and disadvantages of the Foster-Seeley Discriminator, along with a basic overview of its function. It highlights the pros and cons of using this type of FM demodulator.

Different types of modulation and demodulation techniques exist, including those for amplitude, phase, and frequency. Several techniques are used as frequency demodulators or detectors. These include:

• Quadrature detector
• Slope detector
• PLL detector
• Foster-Seeley discriminator
• Ratio detector
• DSP-based FM demodulator

What is a Foster-Seeley Discriminator?

The Foster-Seeley Discriminator is a type of FM detector used to demodulate frequency-modulated signals. It’s also utilized as an AFC (Automatic Frequency Control) component in receivers such as super-heterodyne receivers.

The diagram above shows the circuit of a Foster-Seeley Discriminator. The circuit resembles a full-wave bridge rectifier with a center-tapped transformer.

It employs a tuned version of a transformer to convert frequency variations into amplitude variations. As shown, the transformer is tuned to the desired carrier frequency and connected to rectifier diodes. RF choke, C1, and C2 components block the RF signal from appearing at the output.

Benefits or Advantages of Foster-Seeley Discriminator

The following are the benefits or advantages of the Foster-Seeley Discriminator:

• It provides good performance.
• It offers a fair amount of linearity.
• It is simple to implement using readily available components.
• It delivers a higher output compared to a ratio detector.
• It provides an output with lower distortion compared to a ratio detector.

Drawbacks or Disadvantages of Foster-Seeley Discriminator

The following are the drawbacks or disadvantages of the Foster-Seeley Discriminator:

• It is difficult to integrate this circuit into an IC (Integrated Circuit).
• It is more expensive due to the higher cost of the required transformer.
• It has a narrower bandwidth compared to a ratio detector.
• A limiter is required along with the Foster-Seeley Discriminator because it is sensitive to both frequency and amplitude variations.