Broadcast Radio

Broadcast Radio

Physical Description The principal difference between broadcast radio and
microwave is that the former is omnidirectional and the latter is directional. Thus
broadcast radio does not require dish-shaped antennas, and the antennas need not
be rigidly mounted to a precise alignment.
Applications Radio is a general term used to encompass frequencies in the range
of 3 kHz to 300 GHz. We are using the informal term broadcast radio to cover the
VHF and part of the UHF band: 30 MHz to 1 GHz. This range covers FM radio and
UHF and VHF television. This range is also used for a number of data networking
applications.

transmission characteristics 

The range 30 MHz to 1 GHz is an effective one
for broadcast communications. Unlike the case for lower-frequency electromagnetic
waves, the ionosphere is transparent to radio waves above 30 MHz. Thus transmission
is limited to the line of sight, and distant transmitters will not interfere with
each other due to reflection from the atmosphere. Unlike the higher frequencies
of the microwave region, broadcast radio waves are less sensitive to attenuation
from rainfall.
As with microwave, the amount of attenuation due to distance for radio
obeys Equation (2.2), namely 10 109(4:d)2
dB. Because of the longer wavelength,
radio waves suffer relatively less attenuation.
A prime source of impairment for broadcast radio waves is multipath interference.
Reflection from land, water, and natural or human-made objects can create
multiple paths between antennas. This effect is frequently evident when TV reception
displays multiple images as an airplane passes by.

Infrared 

Infrared communications is achieved using transmitters/receivers (transceivers)
that modulate noncoherent infrared light. Transceivers must be within the line of
sight of each other either directly or via reflection from a light-colored surface such
as the ceiling of a room.
One important difference between infrared and microwave transmission is
that the former does not penetrate walls. Thus the security and interference problems
encountered in microwave systems are not present. Furthermore, there is no
frequency allocation issue with infrared, because no licensing is required.