Unbounded media/unguided media

media doesn't use any physical connectors between the two devices communicating. this is media transport electromagnetic wave withhout physical conductor. signal are broadcasting through air or water and therefore availble to anyone who has a device capable of receiving them. usually the transmission is send through the atmosphere but sometimes it can be just across the rule.

terrestrial microwave

microwaves are radio waves with wavelengths ranging from as long as one meter to as one milimetre, or equivalently, with frenquencies between 300 MHz (0.3 GHz.). require line-sight transmission and reception equipment. towers on hills or mountains. the signal transmit one way direction at a time.

 there has 2 types of antennas:
        1. Parabolic dish
        2. Horn
1. Parabolic dish

A parabolic reflector (or dish or mirror) is a reflective device used to collect or project energy such as light,sound, or radio waves. its shape is that of a cicular paraboloid, that is, the surface generated by a parabola revolving around its axis. the parabolic reflector transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus. Based on geometry of parabola.

2. Horn
it looks like gigantic scoop outgoing transmission are broadcast up a stem & deflected outward in a series of narrow parallel beams by the scooped shape of the horn.

 

3. Satellite
A satellite dish is a dish-shaped types of parabolic antenna designed to receive mircrowaves from communications satellites, which transmit data transmissions or broadcasts, such as satellite television. that satellite is super tall antenne and repeater. single bounce.
capability- any location on earth no matter how remote. it is high quality communication without requiring a huge investment in ground-based infrastructure. same speed as the eart.
Geosynchronous satellite - orbit speed is based on distance from the planet.
minimum 3 satellite  to provide full global transmissions. transmission from earth to satellite  is uplink however transmission from the satellite to earth is downlink.

principle of operation- the parabolic shape of a dish reflects the signal to the dish's focal point. this feedhorn is essentially the front-end of a waveguide that the signal at or near the focal point and 'conducts' them to a low-noise block downconverter or LNB.

4. WI-FI
wi-fi is a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed internet connections. the WI-FI Alliance defines WI-FI as any " wireless local area network (WLAN) products that are based on the institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards.

A device that can use Wi-Fi (such as a personal computer, video game console, smartphone, tablet, or digital audio player) can connect to a network resource such as the Internet via a wireless network access point. Such an access point (or hotspot) has a range of about 20 meters (65 feet) indoors and a greater range outdoors. Hotspot coverage can comprise an area as small as a single room with walls that block radio waves or as large as many square miles — this is achieved by using multiple overlapping access points.

Radio Frequancy
Radio frequency (RF) is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems do exist (see mechanical filter and RF MEMS). Electric currents that oscillate at radio frequencies have special properties not shared by direct current or alternating current of lower frequencies. The energy in an RF current can radiate off a conductor into space as electromagnetic waves (radio waves); this is the basis of radio technology.