Wireless: Start of Ch 4

Supplemental notes for the review of Ch 3. 

High pass aka low cut

Low pass aka high cut

The spike or raised area on any graph shows the BLOCKED frequencies.

Chapter 4 start

Gain and Loss

Understanding RF signal transmission involves the strength or power with which the transmitter is sending out the signal, the amount of reduction in signal strength caused by cables, connectors, and other components, the transmission medium and the minimum strength of the signal required by the receiver to be able to properl recover the data sent by the transmitter. 

An amplifier boosts the power of a signal, called a gain.  Cables and connectors offer a resistance to the flow of electricity and tend to decrease the power of a signal (loss).  Signal power changes logarithmically and gains and loss are relative concepts.  You need to know the power level of the signal at two different points. 

The Decibel

Decibel (dB) is the ratio between two signal levels.  It makes it much simpler to express and calculate power gain or loss.  

Tens and threes of RF mathematics

A gain of (+)3dB means the signal is two times bigger, or twice the power.  A gain of (+)10dB means the signal is 10 times bigger, or 10 times the power.  The same applies for loss.

dBm is a relative way to indicate an absolute power level in the linear Watt scale, ex: 1 mW = 0dBm.  An Isotropic radiator is a theoretical perfect sphere that radiates power equally in all directions.  It provides a reference point for representing the gain of an antenna, and is usually expressed in dB isotropic (dBi).  For microwave and higher frequency anennas gain is usually expressed in dB dipole (dBd).  A Dipole is the smallest, simplest, most practical type of antenna that can be made that also exhibits the least amount of gain.  It has a fixed gain over that of an isotropic radiator of 2.1 db.