Lesson 11 - Radio Frequency Fundamentals
Which one is the better VSWR Ratio and why?
1.1 : 1 or 1.5 : 1 1.1 : 1 - The first number represents the reflected power. The closer to 1 it is the better... = Less impedance
A transmitter outputs 100 mWMilliwatts. An antenna cable connects the transmitter to an amplifier, and the power into the amplifier's input measures 50 mW. The amplifier increases the signal to the original transmitter's power level and sends the signal to the antenna. The antenna receives the signal from the amplifier at 75 mW, and then transmits at 150 mW. What is the IRIntentional radiator's's power level in this RFRadio frequency circuit?
75 mW
How does Radio frequency RF LOS differ from visual LOS?
RF LOS is accompanied by a Fresnel zone, a series of concentric ellipsoid-shaped areas around the visual LOS path
What is IERP
The power delivered to the antenna element from the IR
What is VSWR?
Voltage Standing Wave Ratio. Ratio of forward power versus reverse power.
What is the Fresnel zone?
Zone that'll keep RF/LOS relatively straight so it'll avoid obstructions.
Given an AP (Access point) with 100 mW (Milliwatts) of output power connected through a cable with 3 dB (Decibel) of loss to the antenna with a 10 dBi (Decibels isotropic) gain, what is the approximate EIRP (Equivalent Isotropically Radiated Power) level from the antenna in mW?
500 mW.
What is a variance of high VSWR
A signal being reflected at a point of impendence. Causes the return to have extra loss which goes back to the transmitter. If that's the case then that means the poor return means impedance on the forward.
Diffraction
a rough surface or a surface with sharp irregularities obstructs the radio path between a transmitter and receiver. Diffraction is bending AROUND the medium.
Absorption
occurs when an RF signal strikes an object and is absorbed into the object's material so that it does not pass through, reflect off, or bend around the object. Examples of objects that absorb RF signals are concrete, cement, pavement, wood, and trees.
Scattering
occurs when the medium that a wave travels through consists of objects with dimensions smaller than those of the signal's wavelength, and the number of obstacles per unit volume is large. Stop signs, rocks, sand, and other uneven surfaces.
What is refraction?
the bending of waves due to going THROUGH a denser medium. For example, signal going to a pool of cold air in a valley will cause it to bend and change direction.
What is multipath
Reflection in the main signal due to obstructions in its path.
How much blockage can be allowed before a significant amount of interference occurs.
20% - 40%. Most try to stay on the safe side and allow no more than 20.
What does IR mean
Intentional radiator
What type of antennas does WLANs need to use? LOS or RF
RF! It doesn't behave in the same manner as visual light.
Why is the Fresnel zone important to the integrity of the RF link or path?
The Fresnel zone defines an area around the RF LOS that can introduce RF signal interference if blocked.
What is Reverse Power?
mismatched impedance (resistance to current flow, measured in ohms) between devices in a radio frequency (RF) system
In what manner do radio waves propagate (move) away from the source (antenna)?
In a straight line in all directions at once.
What are some measures that can be taken to prevent high VSWR in transmitters and receivers?
Tighten connections between cables and connectors and use impedance-matched hardware throughout.
What does AC stand for
alternating current, Signal inputting that'll get turned into radio frequencies.
What unit of measurement is used to express the gain of an antenna?
dBi