Foster–Seeley discriminator The Foster–Seeley discriminator[1][2] is a common type of FM detector circuit, invented in by Dudley E. Foster[3] and Stuart. FOSTER-SEELEY DISCRIMINATOR The FOSTER-SEELEY DISCRIMINATOR is also known as the PHASE-SHIFT DISCRIMINATOR. It uses a double-tuned rf. Foster Seeley Discriminator – Download as PDF File .pdf), Text File .txt) or read online. foster.

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Navy Electricity and Electronics Training Series (NEETS), Module 12 – RF Cafe

The Foster Seeley is a common type of FM detector circuit used mainly within radio sets constructed using discrete components. The secondary winding of T1 L2 and capacitor C2 also form a tank circuit tuned to the center frequency.

At resonance the tank acts like a resistive circuit; that is, the tank current is in phase with the primary voltage Ep. All trademarks, copyrights, patents, and other disscriminator of ownership to images and text fosteg on the RF Cafe website are hereby acknowledged.


It uses a tuned RF transformer to convert frequency changes into amplitude changes. Christopher James Christie born September 6, is an American politician, former federal prosecutor, and political commentator who served as the 55th Governor of New Jersey from to Frequency Modulation Tutorial Includes: This gives a signal that is 90 degrees out of phase.

What is the primary advantage of a ratio detector? Point A to point D equals -2 volts. The vector sum of Ep and e2 is larger than that of e and e1. Contract was awarded 9 months later, Foster and Stuart William Seeley in Amplitude modulation suppression A large value reservoir capacitor C4 a Therefore a limiter amplifier stage must be used before the detector, to remove amplitude variations in the signal which would be detected as noise.


The transmitter was switched on and off to produce long or short periods of radio waves, spelling out text messages in Morse code. These voltages cancel each one another out at the output so that no voltage is present. This circuit is basically the same as an AM detector with the tank tuned to a higher or lower frequency than the received carrier.

Foster Seeley Discriminator or FM Detector

R1 and R2 will each have 5 volts dropped across them because they are of equal values. Lawrence University alumni Revolvy Brain revolvybrain. The current flowing in the tank circuit causes diwcriminator e1 and e2 to be developed in the secondary winding of T1.

When an un-modulated carrier is applied at the centre frequency, both diodes conduct, to produce equal and opposite voltages across their respective load deeley. A ratio detector using solid-state diodes The ratio detector is a type of detector circuit, commonly used in radio receivers for demodulatng frequency modulated FM signal.

Both diodes conduct equally. When the tuned circuit is operated at a frequency lower seeley resonance, the capacitive reactance increases and the inductive reactance decreases.

Foster–Seeley discriminator

Invented in by Dudley E. A typical discriminator response curve is shown in figure Above xiscriminator center frequency, diode CR1 conducts more than diode CR2. Therefore a limiter amplifier stage must be used before the detector, Since the diodes are connected as half-wave rectifiers, these small AM signals will be detected as they would be in a diode detector and will appear in the output.


Demodulation is extracting the original information-bearing signal from a carrier wave.

Download our mobile app and study on-the-go. Power management RF technology Test Wireless. In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage. Likewise, the voltage applied to the discrimijator of CR2 is the vector sum of e2 and Ep.

Proceedings of the Institute of Radio Engineersvol. When C3 discharges sufficiently, the quadrature grid becomes positive, grid current flows, and the cycle repeats itself. This is much lower than that required for limiter saturation and less gain is required from preceding stages.

Because the quadrature grid has the same conduction and cutoff levels as the fotser grid, the resultant current waveform will be transformed into a square wave. High cost of transformer. Either grid can cut off plate current. When the input signal reverses polarity, the secondary voltage across Fostrr also reverses. As with any circuit there are a number of advantages and disadvantages to be considered when choosing between the various techniques available for FM demodulation.

Accordingly these circuits are rarely used in modern equipment. Equal anode voltages on diodes CR1 and CR2 produce equal currents and, with equal load resistors, equal and opposite voltages will be developed across R3 and R4. What is the function of serley fm detector? This disadvantage can be eliminated by placing a limiter circuit before the tank input.