Chapter 2. Flashcards
At what speed does a radio wave travel per second?
300,000,000 m/sec
Refraction vs diffraction, what are they, and what causes them, and what environments are they most common?
Refraction: The bending of an RF signal as it passes through a medium with a different density, thus causing the direction of the wave to change. Most common outdoors.
Diffraction: the bending of an RF signal around an object
What actually happens to a wave that is suffering from attenuation?
Amplitude is lost, which defines the power an RF wave has.
What are skywave reflections?
This phenomenon occurs with very long RF signal wavelengths; usually below 1 GHz. This occurs when the signal bounces off of charged particles of the ionosphere in the earths atmosphere.
What does a radio wave start as, as it begins its journey down a coaxial cable?
Alternating Current (AC)
What GHz range does microwave use?
1-300 GHz
What is an RF shadow?
Sitting directly behind the cause of diffraction. Directly behind a large column or pole. This could be an RF dead zone.
What is Aperture?
The effective area for receiving power from a transmitter.
What is data corruption in terms of multipath?
Because of the difference in time between the primary signal and the reflected signals known as the delay spread, along with the fact that there may be multiple reflected signals, the receiver can have problems demodulating the RF signal information.
What is delay spread?
The time differential between signals that are broken apart from the main principle wave on getting to the receivers appassure.
What is downfade?
What is upfade?
What is nulling/cancellation?
This is decreased signal strength (due to multipath). When the multiple RF signals paths arrive at the receiver at the same time and are out of phase with the primary wave, the result is a decrease in signal strength.
Upfade is the benefit from multipath
Nulling/Cancellation is when the multipath waves completely cancel each other out
What is free space path loss?
The loss of signal strength caused by the natural broadening of RF waves.
What is nulling?
This is signal cancellation. When the multiple RF signal paths arrive at the receiver at the same time and are 180 degrees out of phase with the primary avem resulting in a nulling, or cancellation.
What is oscillation?
The fluctuation of voltage in an AC current.
What is Received amplitude?
the strength of a received RF signal
What is Reflection
When a wave hits a smooth object that is larger than the wave itself, depending on the media the wave may bounce in another direction.
What is scattering? What are the two types?
Scattering can most easily be described as multiple reflections. These multiple reflections occur when the electromagnetic signal’s wavelength is larger than pieces of whatever medium the signal is reflecting from or passing through.
- Less effect on signal : When an RF signal moved through a substance and the individual electromagnetic waves are reflected off the minute particles within the medium.
- Heavy effect on signal : When an RF signal encounters some type of uneven surface and is reflected multiple directions. Chain link fences, wire mesh in stucco walls or old plaster walls, rocky terrain……
What is the most common occurrence of destructive multipath? What is a common name for it? What prevents these errors from making its way up to layer 3?
Data Corruption. Intersymbol Interference. CRC value will be wrong, and the frame will be rejected as corrupt.
What is the most common RF behavior? What does it do?
Absorption.
If a signal does not bounce off an object, move around the object, or pass through an object, then 100 percent absorption has occurred. These are objects like brick walls which absorb RF very well.
What is the natural broadening of RF waves called?
Beam Divergence
What is the relationship between the speed of a signal and its wavelength?
A simplified explanation is that the higher the frequency of an RF signal, the smaller the wavelength of that signal. The larger the wavelength of an RF signal, the lower the frequency of that signal.
What is Transmit amplitude?
Typically defined as the amount of initial amplitude that leaves the radio transmitter.
What is upfade?
This is increased signal strength. When multiple RF signal paths arrive at the receiver at the same time and are in phase or partially out of phase with the primary wave, the result is an increase in signal strength.
What is waveform?
The shape and form of the AC signal.
