Basics

Navigation :
                  Determination of position and velocity (speed with direction) of a moving object is navigation .It's a field of study that focuses on the process of monitoring and controlling of a moving object from one place to another.Generally this field consist of four categories ; land navigation,space navigation,marine navigation and aeronautic navigation.

Air Navigation :
                   Process of controlling movement of a craft from one place to another.Ensurin safety of people on board and on ground.

Radio Wave Propagation :

                   Radio waves can propagate in air through various ways.These includes 

•  ground waves
•  ionosphere waves
•  space waves 
•  tropspheric waves

Ground Waves :

• travels close to surface of earth and propagate for relatively short distance at HF and VHF.but for greater distance at MF and LF.
• It has two basic components

1. Direct waves
2. Ground reflected waves

Direct Waves :
                   are often reffered as sapce waves ,such waves travels at line of sight at VHF,UHF and beyond.

Ground Reflected Waves :

• waves reflected from ground
• not complete incident waves is reflected from ground,some part of it is obsrbed in ground.       
• sandy soil is a poor reflector whereas flat marshy ground is an excelent reflector            

Four different effects can occur to a radio signal.

Reflection : 

• when a plane wave meets a plane object that is large relative to wavelength of signal.
• wave is reflected back with minimal distortion and without change in velocity.

Difrraction:

                  occurs when a wave move from one medium to anotherin which it travels at a different speed. 

Scaterring : 

                  occurs when a wave meets one or more object at its path having size that is fraction of wavelength of signal

Troposphric ducting :

                  in which radio signals can become trapped as a result of change of refractive index at a boundry between air masses havind differnt temperature and humidity.

MUF : 
             highest frequency that will alow communication over a given path at a particular time on a particular date.

LUF : 

             lowest frequency that will alow communication over a given path at a particular time on a particular date.