# Avionics MCQs – Radio Transmitters

1 - Question

The transmission of data by dots and dashes is an example of ___________
a) Amplitude modulation
b) Frequency modulation
c) Continuous wave transmission
d) Discrete signal transmission
Explanation: The oscillator generates the carrier and can be switched off and on by a telegraph key to produce the dots and dashes of the International Morse code. Information transmitted in this way is referred to as continuous-wave (CW) transmission. Such a transmitter is rarely used today.

2 - Question

What device is used to prevent power from the transmitter from going to the receiver side?
a) Multiplexer
b) Duplexer
c) Monoplexer
d) Filter
Explanation: A duplexer is a device that is placed just before the antenna in a transducer system. It is basically a switch which allows both transmission and reception but only one at a time.

3 - Question

What generates the final carrier frequency?
a) Oscillator
b) Modulator
c) Antenna
d) Power source
Explanation: An oscillator, in most applications a crystal oscillator, generates the final carrier frequency. A modulator simply adds the information signal and an antenna transmits the signal.

4 - Question

Frequency multiplier multiplies the frequency deviation produced by the modulator.
a) True
b) False
Explanation: The frequency multiplier increase the carrier frequency to the desired output frequency, but also it multiplies the frequency deviation produced by the modulator. The design of the transmitter must be such that the frequency multipliers will provide the correct amount of multiplication not only for the carrier frequency but also for the modulation deviation.

5 - Question

______ is used to provide continuous tuning over the desired range?
a) Variable frequency oscillator
b) Frequency synthesizer
c) Variable Frequency producer
d) Frequency multiplier
Explanation: A variable frequency oscillator (VFO) is used to provide continuous tuning over a desired range. Using VFO different carrier frequencies can be generated.

6 - Question

What is the only oscillator capable of meeting the precision and stability demanded by the FCC?
a) Armstrong Oscillator
b) Crystal Oscillator
c) Hartley oscillator
d) RC Phase Shift Oscillator
Explanation: The transmitter must remain on the assigned frequency. It must not drift off or wander from its assigned value despite the many operating conditions, such as wide temperature variations and changes in power supply voltage, that affect frequency. The only oscillator capable of meeting the precision and stability demanded by the FCC is a crystal oscillator.

7 - Question

The device that maintains controlled temperature for crystal oscillators are called __________
a) Crystal stove
b) Crystal ovens
c) Crystal chamber
d) Temperature chamber
Explanation: greater stability of crystal frequency can be achieved by mounting the crystal in sealed, temperature-controlled chambers known as crystal ovens. These devices maintain an absolute constant temperature, ensuring a stable output frequency.

8 - Question

What is the maximum frequency of a 16-MHz crystal with a stability of 200 ppm?
a) 1,60,03,200Hz
b) 2,14,65,400Hz
c) 1,36,12,500Hz
d) 4,56,42,863Hz
Explanation: The frequency can vary as much as 200 Hz for every 1 MHz of frequency or 200×16=3200Hz. The maximum frequency is 1,60,00,000 + 3200 = 1,60,03,200 Hz.

9 - Question

Calculate the transmitter output frequency if the transmitter uses a crystal oscillator with a frequency of 14.9 MHz and a frequency multiplier chain with factors of 2, 3, and 3.
a) 1.564MHz
b) 268.2MHz
c) 264.3MHz
d) 265.6MHz
Explanation: Total frequency multiplication factor 2 x 3 x 3 = 18 Transmitter output frequency = 14.9 MHz x 18 = 268.2 MHz.

10 - Question

Calculate the frequency for maximum drift of crystal if The crystal has a stability of 6300 ppm and an output frequency of 268.2MHz and frequency multiplier chain with factors of 2, 3, and 3.
a) 123.5MHz
b) 423.2MHz
c) 269.65MHz
d) 235.1MHz
Explanation: Variation = 300ppm = 0.03% This variation is multiplied by the frequency multiplier chain, yielding 0.03 percent x 18 =60.54 percent. Now, 268.2 MHz x 0.0054 = 1.45 MHz. Thus, the frequency of the transmitter output is 268.2 + 1.45 MHz. The maximum frequency is 268.2 + 1.45 = 269.65 MHz.

11 - Question

What is the minimum frequency of a 16-MHz crystal with a stability of 200 ppm?
a) 1,60,03,200Hz
b) 2,14,65,400Hz
c) 1,59,96,800Hz
d) 4,56,42,863Hz