ELECTIVE 1

Troposphere

thicker at the equator and thinner near the poles

stratosphere

protects earth by absorbing harmful ultraviolet radiation from the sun

mesosphere

coldest layer of the atmosphere with very little air. most meteor burn up here due to the friction with the air, helping protect earth from potential impacts

10-15km to 50km

stratosphere height

50km to 85km

height of mesosphere

85km to 600km

thermosphere height

thermosphere

despite high temperature, it would feel very cold to humans because the air is extremely thin

thermosphere

this is where auroras or southern lights occur, and contains the international space station and many satellites

exosphere

contains very few particle and almost no air present

600km to 10000km

height of exosphere

exosphere

some satellites orbit in this layer, and it marks the transition from earth’s atmosphere into space

carbon dioxide, nitrogen, oxygen, water vapor, trace gases

composition of the earth’s atmosphere

sun radiation

what causes molecules and atom to become ionized

ideal electromagnetic waves

propagate through a perfect vacuum, they travel in a straight line from the transmitter to the receiver

refraction of radio waves

how does direction affect radio waves

attenuation

signal becomes weaker. atmospheric effects can contribute to this loss through mechanisms such as absorbtion and scattering.

direction, range, attenuation, speed

what affects radio waves

3x10^8

value of speed of light in terms of vacuum

surface/ ground wave propagation

transmition of radio waves along the earth’s surface

lower frequency waves

travel farther due to the ability to diffract around obstacles

higher frequency

more susceptable to interference

ground reflection

depends heavily on the electrical properties of the ground.

sandy soil

poor reflector of radio signals

flat marshy terrain

excellent reflecting surface

sky wave propagation

thrown into ionosphere to receiver. good for long distance communication

radio waves and ionospheric

factors that affects sky wave propagation model - frequency of _______ and ____condition

MF, HF, VHF

sky wave propagation required frequency

diffraction

occurs when a wave encounters an edge or an obstace whose dimension are large relative to the wavelength signal.

scattering

when a wave encounters ome or more object in its path whose dimensions are a fraction of the signal’s wavelength.

scattering

when this type of obstruction is present the wave becomes fragmented and re radiated over a wide angle

scattering

more common in high frequency typically vhf and above and frequency observed in the troposphere at UHF and EHF

tropospheric scattering

analogous to the way a light beam such as a torch, scatters when directed into a heavy fog or mist

tropospheric ducting

condition in which radio signal becomes trapped due to a change in a refractive index at the boundary between air masses with different temperature and humidity.

temperature inversion

typically occurs when a large mass of the cold air is overrun by warm air and typically known as a

ducting

not highly predictable and therefore is not used for practical communication application

line of sight propagation

transmission of radio waves in a straight line, free from any obstruction or reflection

line of sight propagation

finds extensive use in various application like wireless communication, radar system, and sattelite communication

ionosphere

discovered by sir edward appleton thw onw that demonstrate the existing of a reflective layer at a height of 100km which is the E LAYER and 250km THE F LAYER

ionosphere

upper portion of the atmosphere that absorbs large amount of radiant energy from the sun. causing it to become heated and ionized

d layer

responsible for absorption of radio waves at lower frequency below 4 Mhz during daylight hours

E layer

responsible for the reflection of radio waves with frequency below 5 MHz and absorbs the one above it

E Layer

develops shortly after sunrise and fades a few hours after sunset, reaching maximum ionization around mid day

Sporadic layer

ES layer is also known as?

highly reflective at frequency above 30 MHz and on some occasions up to 300Mhz and has no other use other tha enabling long distance VHF communication for radio amateurs.

ES Layer

most common during summer months with peak activity in june and july. persist for only a few hours, of then forming in the late morning and recurring in the early evening

F layer

most important layer for long distance radio communication

20-25 MHz

F layer is capable of reflecting up to __

F1 layer

forms during daylight hours reaching maximum ionization around mid day capable to reflect up to 10MHz

F2 layer

max ioinization one hour after sunrise till shortly after sunset

maximum usable frequency

highest frequency that can be used for a particular radio‑communication path under specific ionospheric conditions. It may vary with time, location, solar activity, and path geometry.

maximum usable frequency

If the operating frequency exceeds this limit, the sky‑wave signal may penetrate the ionosphere or return to a different location instead of the intended receiving area.

lowest usable frequency

lowest frequency that can provide usable communication for a particular radio path under specified conditions. However, it is not optimal to stay on the lowest usable frequency due to greater absorption especially in lower ionosphere.

Lowest usable frequency

If the operating frequency didn’t reach this limit, the sky‑wave signal may experiences excessive absorption/attenuation and arrive at the receiver too weakly for reliable communication.

CRITICAL FREQUENCY

highest frequency for a given layer that will return down to earth vy that layer after beamed up straight to it

(9x10^-3) sqrt of electron density N

critical frequency formula

Silent zone

located between regions both closer and farther from the transmitter when reception is possible. A skip zone, also called a silent zone or zone of silence, is a region where a radio transmission can not be received.

yes

when a signal returns to Earth from the ionosphere, it may sometimes be reflected by the ground. The reflected signal will experience attenuation; however, under certain conditions, it may still be strong enough to produce an additional hop, effectively doubling the working range.

Fading

At times, signals may be received simultaneously via both ground-wave and sky-wave paths. These signals can combine constructively or destructively due to differences in path length, producing an effect known as

Skip distance

distance between the point at which the sky wave is radiated and the point at which it returns to Earth is known as