30 Questions
What is a radio signal composed of?
Electric and magnetic fields
What causes the electric and magnetic fields in an antenna?
Voltage applied to the antenna
How are the electric and magnetic fields oriented in a radio signal?
They are at right angles to each other
What is the speed at which electric and magnetic fields propagate through space?
The speed of light
How are the polarities of the wires in a transmission line related?
They have opposite polarities
Why do transmission lines not radiate radio signals efficiently?
They are not designed to radiate signals
What is the measure of an antenna's directivity?
Beam width
How is beam width measured on an antenna's radiation pattern?
Between points that are 3 dB down from the maximum amplitude
What is antenna gain expressed as?
Ratio of effective radiated output power to input power
What impedance does a dipole antenna have at its center?
73 ohms
At what frequency does a dipole antenna appear to be a pure resistance of 73 ohms?
Resonant frequency
What is important for maximum power transfer in a dipole antenna?
Matching the impedance of the transmission line to the load
Which layer of the ionosphere is divided into the F1 and F2 layers?
The F layer
What is the primary effect of the F layer on radio signals?
Refracting radio signals as they cross layer boundaries
At what angle do radio signals pass directly through the ionosphere without being refracted?
$90^\circ$
Which layers of the ionosphere exist only during daylight hours?
The D and E layers
What happens to radio signals at very high frequencies above 50 MHz?
They pass through the ionosphere without refraction
What is the result of radio waves being reflected by the ionosphere?
The signal is propagated over an extremely long distance
What is the relationship between the angles and indices of refraction called?
Snell's law
What happens when an obstacle appears between a transmitter and receiver?
A shadow zone is created where some of the signal is blocked
Which of the following is NOT one of the three basic paths that a radio signal can take through space?
Ionospheric wave
What type of polarization is required for ground waves to be propagated from an antenna?
Vertical polarization
In which frequency range are ground waves the main signal path?
30 kHz to 3 MHz
What is the index of refraction for air, compared to the speed of a wave in a vacuum?
Very close to 1
What is the nature of the magnetic field generated by an antenna?
The magnetic field varies sinusoidally in accordance with the applied signal from the generator.
What is the relationship between the electric and magnetic fields in an electromagnetic wave?
The electric and magnetic fields support and sustain each other in an electromagnetic wave.
What is the wave impedance of space, which is the ratio of the electric field strength to the magnetic field strength of a radiated wave?
377 Ω
At what speed are the resulting electromagnetic fields radiated into space?
The speed of light ($3 \times 10^8$ m/s)
What is the role of the antenna radiation resistance in an antenna?
It represents the resistive component of the antenna that consumes power as radiated electromagnetic energy.
What are the two sets of fields produced by an antenna?
The near field and the far field
Learn about the basic principles of antennas in the context of radio and TV engineering. Understand how radio signals are composed of electric and magnetic fields, and how antennas emit these fields to propagate signals.
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