Ham Radio Exam Preparation 3

The output signal of a CE amplifier will be:
a) 45 deg out of phase
b) 90 deg out of phase
c) 180 deg out of phase
d) 270 deg out of phase

The most common type is common emitter configuration in which emitter is grounded, base acts as the input and collector as the output. So the input is given between the base and the emitter which is grounded. Current gain in this configuration, which is the ratio of collector current to the base current is known as beta or hFE, which stands for Hybrid parameter Forward current gain, common Emitter. Beta is always more than 1. This configuration has medium input and output impedance levels. Both current and voltage gains are medium. There is a 180 degree phase change between input and output, so that output is the inverse of the input.

An Oscillator is based on
a) Positive feedback
b) Negative feedback
c) No feedback
d) Both a & b

Oscillator in electronics is a circuit which produces periodic oscillations or alternating signal which could be a sine wave, square wave or another type of wave. The oscillator is powered by a direct current source and can be used in a wide variety of applications like radio, television, computer and mobile phone. In the animation, a resistor-capacitor (RC) network is used to feed a portion of the output of the inverting Schmitt trigger into its input. Schmitt trigger is a circuit with hysteresis implemented by applying positive feedback to the non inverting input of a differential amplifier. It is called a trigger because the output retains its value till the input changes sufficiently to trigger a change. That brings us to the most common form of linear oscillator or harmonic oscillator in which a transistor or operational amplifier is connected in a feedback loop with output fed back into its input through a frequency selective electronic filter to provide positive feedback. In the illustration, the RC network does this job. 

The output signal of a detector in a communication receiver is in
a) Audio Frequency range
b) Radio Frequency range
c) Intermediate Frequency range
d) None of the above

Typically detection is the process of extracting the modulating signal from the radiofrequency signal received by the radio. So output signal will be in the audio frequency range. Intermediate frequency is the output of the mixer which mixes the received signal in a superheterodyne receiver with a local oscillator signal. In double conversion receivers there will be two intermediate frequencies, while in the direct conversion receiver there is no intermediate frequency. That is because local oscillator frequency in a direct conversion receiver is at or very near that of the received radio frequency signal.

The following type of Oscillator will be more stable
a) RC Oscillator
b) Hartley Oscillator
c) Colpitts Oscillator
d) Crystal Oscillator

Crystal oscillators are more stable than other types of oscillators. But the disadvantage is that they can operate only on a fixed frequency. Even frequency of crystals can drift with change in temperature as the quartz crystal can expand or contract. That is why in high precision equipment, crystal temperature is controlled, typically in a warmed chamber known as crystal oven. Then they are called oven-controlled crystal oscillator (OCXO). Other methods of stabilization are with analog circuits to compensate drift in frequency with temperature known as TXCO or temperature compensated crystal oscillator and microcontroller compensation known as MCXO.

For a Step-down Transformer, the relation between the number of
turns in primary (Np) and the number of turns in secondary (Ns) is
a) Np > Ns
b) Ns > Np
c) Ns = Np
d) None of the above

For a step down transformer, the number of turns in the primary winding is higher. In case of step up transformer, secondary winding has more number of turns. The turns ratio between the primary and secondary windings gives the ratio between the primary and secondary voltages.