Frequency-Shift Keying Modulation Quiz

What is the purpose of capacitor C5 in the modulating signal circuit?

To provide a path for the modulating signal to the varactor
To filter the modulating signal
To block the DC varactor bias from the modulating signal circuits (correct)
To couple the modulating signal to the RF choke

What is the purpose of the tuned circuit formed by L2 and C1 in the slope detector?

To amplify the FM signal
To convert frequency variations to voltage variations (correct)
To filter the FM signal
To generate the FM signal

How does the slope detector output voltage change when the frequency of the FM signal goes lower than the carrier frequency?

The output voltage first increases and then decreases
The output voltage decreases (correct)
The output voltage remains the same
The output voltage increases

What is the purpose of the diode detector in the slope detector circuit?

To rectify the AC voltage across C1 into DC pulses (A) Signup and view all the answers

What is the purpose of the radio frequency choke (RFC) in the modulating signal circuit?

To provide a path for the modulating signal to the RF stage (A) Signup and view all the answers

How does varying the resistance of R4 affect the center carrier frequency of the FM signal?

It increases the carrier frequency (B) Signup and view all the answers

In frequency modulation (FM), what remains constant?

Carrier amplitude (C) Signup and view all the answers

What happens to the carrier frequency when the amplitude of the modulating signal increases?

The carrier frequency increases (A) Signup and view all the answers

Which term refers to the amount of change in carrier frequency produced by the modulating signal?

Frequency deviation (B) Signup and view all the answers

When does maximum frequency deviation occur in FM?

At the maximum amplitude of the modulating signal (A) Signup and view all the answers

In binary frequency modulation, how many values can the carrier frequency have?

Two values (B) Signup and view all the answers

What determines the amount of shift in carrier frequency in binary frequency modulation?

The amplitude of the binary signal (B) Signup and view all the answers

What is the purpose of the reverse-biased junction diode in the circuit?

To act as a small capacitor (C) Signup and view all the answers

How does the width of the depletion layer affect the capacitance of the reverse-biased junction diode?

Wider depletion layer results in lower capacitance (C) Signup and view all the answers

What is the purpose of the capacitor $C_1$ in the circuit?

To block the DC bias on the base of $Q_1$ from being shorted to ground through $L_1$ (A) Signup and view all the answers

What is the purpose of the potentiometer $R_4$ in the circuit?

To adjust the DC bias on the varactor diode $D_1$ (D) Signup and view all the answers

What is the purpose of the inductor $L_1$ in the circuit?

To set the center frequency of the oscillator (D) Signup and view all the answers

What is the typical range of capacitance values for varactor diodes?

1 pF to 200 pF (C) Signup and view all the answers

What is the purpose of the zero-crossing detector or clipper-limiter in the pulse-averaging discriminator?

To generate a binary voltage-level change on each cycle of the FM signal (C) Signup and view all the answers

What is the purpose of the one-shot multivibrator in the pulse-averaging discriminator?

To generate a fixed-amplitude, fixed-width DC pulse on the leading edge of each FM cycle (C) Signup and view all the answers

What is the purpose of the low-pass filter in the pulse-averaging discriminator?

To average the DC pulses from the one-shot multivibrator and recover the original modulating signal (C) Signup and view all the answers

What is the purpose of setting the one-shot multivibrator duration to be less than one-half the period of the highest frequency expected during maximum deviation?

To ensure that the one-shot pulses do not overlap (D) Signup and view all the answers

What is the main advantage of the pulse-averaging discriminator over other FM demodulation techniques?

It can recover the original modulating signal without amplitude variations (B) Signup and view all the answers

What is the name of the modulation widely used in Bluetooth headsets and wireless speakers?

Frequency-Shift Keying (FSK) (A) Signup and view all the answers

What are the side frequencies produced when a constant-frequency sine wave modulates a carrier?

Sum and Difference of the carrier and modulating frequency (B) Signup and view all the answers

What is the modulation index in FM systems?

The ratio of frequency deviation to modulating frequency (C) Signup and view all the answers

In standard FM broadcasting, what is the maximum permitted frequency deviation?

75 kHz (D) Signup and view all the answers

How is the carrier frequency generated in a frequency modulator?

By an LC or a crystal oscillator circuit (B) Signup and view all the answers

What determines the carrier frequency in an LC oscillator?

The values of inductance and capacitance in a tuned circuit (D) Signup and view all the answers