Chapter 2 - Electronic Fundamentals for Communications

What is capacitive reactance (Xc) ?

An opposition to alternating current is caused by a capacitor.

What is Attenuation?

Attenuation refers to a loss introduced by a circuit or component.

What's the relationship between Bandwidth, Frequency and Quality Factor?

BW = Fr/Q

What are Tuned Circuits made up of?

Circuits made up of inductors and capacitors that resonate at specific frequencies.

What is the relationship between the bandwidth of a circuit and its Quality factor (Q)?

The bandwidth of a circuit is inversely proportional to Quality Factor

What are half-power points?

The current levels at which the response is down 70.7 percent because the power at the cutoff frequencies is one-half the power peak of the curve. P = I^2 * R = (0.707 * Ipeak)^2 * R = 0.5 * Ipeak^2 * R

What are Decibels?

The gain or loss of a circuit is usually expressed in decibels (dB),

What is the Quality Factor (Q) of an inductor?

The ratio of inductive power to resistive power

What is Skin Effect?

The tendency of electrons flowing in a conductor to move near and on the outer surface of the conductor frequencies in the VHF, UHF, and microwave regions.

What happens to Xl and Xc during resonance of a Series RLC Circuit?

They are equal, which results in the total impedance comprising of a resistive component alone.

How do you calculate the total gain of cascaded gains?

They are multiplied by one another.

Above the resonant frequency, the circuit is inductive, and the current will lag the applied voltage. True or False

True

Above the resonant frequency, the inductor voltage drop is greater than the capacitor voltage drop. True or False?

True

At very low frequencies, In addition, because the circuit is predominantly capacitive, the current leads the voltage by nearly 90°. True or False?

True

At very low frequencies, XC goes down and XL goes up. The amount of leading phase shift decreases.

True

At very low frequencies, therefore, the current in the circuit is very low because of the high impedance. True or False?

True

Below resonance, the capacitor voltage drop is higher than the inductor voltage drop. True or False?

True

Capacitance causes the current to lead the applied voltage True or False?

True

Does a 2:1 ratio represents a 3-dB power gain or a 6-dB voltage gain. True or False

True

In any wire or conductor exhibits a characteristic inductance. The longer the wire, the greater the inductance. True or False

True

Ratios less than 1 give negative decibel values True or False?

True

Resonance in a series tuned circuit can also be defined as the point at which the circuit impedance is lowest, and the circuit current is highest. True or False?

True

The bandwidth is approximately centered on the resonant frequency. True or False?

True

The bandwidth of a resonant circuit defines its selectivity, i.e., how the circuit responds to varying frequencies. True or False?

True

The bandwidth of a resonant circuit is determined by the Q of the circuit. True or False?

True

The wire leads of a capacitor have resistance and inductance, and the dielectric has leakage that appears as a resistance value in parallel with the capacitor. True or False?

True

What is Inductive Reactance (Xl)?

When an inductor is used in an ac circuit, this opposition becomes continuous and constant and is known as inductive reactance.

What is the working mechanism of an Inductor (Inductance)?

When current is passed through a coil, a magnetic field is produced around the coil. If the applied voltage and current are varying, the magnetic field alternately expands and collapses. This causes a voltage to be self-induced into the coil winding, which has the effect of opposing current changes in the coil.

Why is expressing gain or attenuation in decibels not always a very good idea?

When the ratio is computed, the units of voltage or power are canceled, making the ratio a dimensionless, or relative, figure. When you see a decibel value, you really do not know the actual voltage or power values.

What is the relationship between the reactance of a capacitor (C) and it's operating frequency (F).

Xc = 1 / (2 * π * F * C)

What is the expression for Inductive reactance (Xl)?

Xl = 2 * π * F * L

Is the Quality factor (Q) is a function of the circuit resistance?

Yes. A low resistance produces a high Q, a narrow bandwidth, and a highly selective circuit. A high circuit resistance produces a low Q, wide bandwidth, and poor selectivity.

How do you calculate the overall decibel gain or attenuation of a circuit or system

You simply add the decibel gain and attenuation factors of each circuit

What is the mathematical representation of the total impedance of a Series RLC Circuit?

Z = sqrt(R^2 + (Xl-Xc)^2)

What are cut-off frequencies?

cutoff frequencies occur where the current amplitude is 70.7 percent of the peak current. i.e (0.707 * Ipeak)

What is the bandwidth of the tuned circuit

it is defined as the difference between the upper and lower cutoff frequencies: BW = F2 - F1

What is the mathematical representation of the Quality Factor (Q) of an inductor?

Q = I^2 * Xl / I^2 * R = Xl / R

What is Reactance?

Reactance is an opposition that directly affects the amount of current in a circuit.

What is the bandwidth?

The *narrow* frequency range over which the current is highest is called the bandwidth.

What are the physical factors affecting the inductance of a coil?

* The number of turns of wire * The spacing of the turns * The diameter of the coil * The type of magnetic core material.

The least perceptible sound (hearing threshold)

0 dB

How do you calculate dBm?

10 * log10 (Po / 0.001) in Watts

What is the formula for calculating Decibel gains or losses for Power?

10 * log10 (Po / Pin)

The pain threshold of sound.

120 dB

What is the formula for calculating Decibel gains or losses for Voltage and Current?

20 * log10 (Vo / Vin) 20 * log10 (Io / Iin)

The Intensity of a Normal Conversation?

65 dB

What is 1/10 a decebel?

A bel

What are the functions of Capacitors in A.C. circuits?

A capacitor used in an ac circuit continually charges and dis- charges. A capacitor tends to oppose voltage changes across it.

What comprises a tuned circuit?

A tuned circuit is made up of inductance and capacitance and resonates at a specific frequency, the resonant frequency.

____ was a unit of measurement that was originally created as a way of expressing the hearing response of the human ear to various sound levels.

Decibel

How do you calculate the total gain of a cascaded circuit?

Each circuit gain is multiplied by the next.

How do you calculate the attenuation factor of a cascaded circuit?

Each circuit loss is multiplied by the next.

What is the relationship between the Bandwidth, Cut-off Frequency and Resonant Frequency?

F1 = Fr - BW/2 & F2 = Fr + BW/2

Inductance does not causes the current to lag the applied voltage. True or False?

False

It is not common in communication systems and equipment to cascade circuits and components that have gain and attenuation. True or False

False

Reactive components do not produce a phase shift between the currents and voltages in a circuit. True or False

False

Above the resonant frequency, the inductive reactance is lower than the capacitive reactance True or False?

False It is higher

Below resonance, the capacitive reactance is lower than the inductive reactance True or False

False It is higher

Below resonance, the net reactance is capacitive, thereby producing a lagging current in the circuit. True or False

False The current produced is leading.

At very high frequencies, the capacitive reactance is much greater than the inductive reactance. True or False?

False. At very low frequencies, the capacitive reactance is much greater than the inductive reactance.

If the circuit Q is very low (>100), then the response curve is approximately symmetric around the resonant frequency. True or False?

False. If the circuit Q is very high (>100), then the response curve is approximately symmetric around the resonant frequency.

skin effect Increases the Q of an inductor at the higher frequencies, causing unexpected and undesirable effects. True or False

False. It reduces the Q of an inductor

What is the mathematical relationship between the resonant and cut-off frequencies (on a linear scale)?

Fr = (F1 + F2) / 2

What is the mathematical relationship between the resonant and cut-off frequencies?

Fr = sqrt(F1 * F2)

What is Gain? and what's it's ration

Gain means amplification. Output/Inside

What is the basic unit for Inductance?

Henry

How do you characterise a narrow bandwidth?

If the response is to produce a high current only over a narrow range of frequencies, a narrow bandwidth, the circuit is said to be highly selective.

What is dBm?

It is a reference value used to compare any other value when calculating gain or attenuation. Usually When a decibel value is computed by comparing a power value to 1 mW

What are Inductors?

It is simply a winding of multiple turns of wire.