Lecture 2 - RF Fundamentals

Radio Frequency
Fundamentals
(1 September 2006)
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Describe the behavior of RF
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Explain the properties of an RF signal
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Understand the nature of the intentional
Radiator and EIRP
Objectives
Upon completion of this lecture you will be able to:
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What is RF?
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RF Behaviors
✔
Reflection
✔
Refraction
✔
Diffraction
✔
Scattering
✔
Absorption
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Gain and Loss
Radio Frequency

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Radio Frequencies are high frequency alternating
current (AC) signals that pass along a copper
conductor and then radiated into the air via an
antenna.
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The Antenna
✔
Coverts the wired signal into a wireless signal and
✔
Converts the wireless signal into a wired signal.
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The RF propagates from the antenna in a straight
line in all directions.
Radio Frequency
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Alternating Sine Wave
Fundamental Characteristics
1. Amplitude
2. Frequency
3. Phase
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Wavelength = 300,000,000 meters per sec/Frequency in Hz.
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Length of one wave at a specific frequency.
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As the frequency increases the wavelength decreases.
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A frequency is the number of wavelengths per unit time

1 cycle /second = 1Hz
1,000 cycles/second = 1Khz
1,000,000 cycles /second = 1Mhz
1,000,000,000 cycles/second = 1Ghz
Wavelength vs Frequency
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Electromagnetic Frequency Spectrum
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Wavelength = Speed of Light/Frequency
Visible Light
Fiber Optic
Electromagnetic Spectrum
800
850
1300
1500
Micro = 1 x 10
-6
Nano = 1 x 10
-9
Pico = 1 x 10
-12
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Gain describes an increase in the RF
signal's Amplitude. An external source is
normally used to amplify the signal.
✔

RF Amplifier amplifies the signal while a
✔
Directional High-gain antenna focuses the beamwidth to
increase the signal amplitude.
✔
Reflected signals combined with the main signal can
cause gain.
RF Behavior
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Loss describes a decrease in signal strength.
Loss is caused by such things as:
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Resistance of cables
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Resistance in connectors.
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Impedance mismatch can cause a signal to be reflected back
toward the source.
✔
Objects such as trees or buildings in the transmission path can
cause the signals to be absorbed or reflected.
✔
RF Attenuators and accurate resistors convert frequency to heat to
reduce the signal amplitude.
RF Behavior
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Reflection occurs when a propagating electromagnetic wave
impacts an object with dimensions larger than the wavelength

of the propagating wave.
✔
Reflections can be caused by the earth, buildings, walls, lakes,
metal roofs, metal blinds, metal doors, etc.
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Reflections of the main signal from many objects is referred to
as multipath.
✔
Multipath can degrade or cancel a signal at the receiver.
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Antenna diversity is normally used to overcome Multipath.

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Refraction describes the bending of radio waves as they
pass through a medium of different density.
✔
For example, RF waves passing through different density of the
atmosphere may change direction away from the receiver.
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Absorption occurs when the RF signal strikes an object and
is absorbed rather than being reflected, refracted or bent.
RF Behavior Contd
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Reflection
Refraction