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19
Why more radio stations received at night
than that of the daytime?
Medium wave propagation mainly relies on the ground
wave. Only a small amount of medium wave is transmitted
by relying on sky wave.
When a radio wave encounters conductor, conductor will
generate induced current, consuming a portion of energy.
The phenomenon that weakens the radio wave energy is
called the absorption of radio wave.
The ground is a conductor, which has high absorption of
medium wave. So, the medium wave cannot be transmitted
for a long distance in the form of ground wave (about two
or three hundred kilometers).
Due to sunlight and ionization density increase during the
daytime, the ionosphere becomes a good conductor, such
that a small part of the medium waves propagated in the
form of sky wave will be strongly absorbed, and difficult
to return to the ground. Moreover, the medium waves
propagated in the form of ground wave are absorbed by the
earth and can’t be transmitted for a long distance. So it is
difficult to receive the medium wave radio stations during
the daytime.
At night, the atmosphere is not subject to sunlight, and the
mutual recombination of ionospheric electrons and ions is
significantly increased. Hence, the ionosphere becomes
thinner, the density becomes smaller, the conductivity
becomes poorer, and the radio wave absorption is also
greatly weakened. At this time, the medium wave can be
transmitted to a remote place through sky wave, so the
more medium wave radio stations could be received at
night.
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20
What factor will affect broadcasting
reception effect?
The reception environment is the main factor that affects
the broadcast reception!
In the receiving environment in modern city, there are
many waves that may interfere with the radio, such as FM
radio, wireless phone, personal computer switching power
supply and powerful shortwave SSB communication
station. It is very difficult to listen to shortwave programs
near such places; furthermore, various motors, cars,
televisions, microwave ovens, SCR equipment, and the
fluorescent lamps and poor quality energy-saving lamps
that use electronic rectifier will seriously affect the
medium wave broadcasting.
The mutual interference of a large number of FM radio
stations and VHF TV will also make the FM radio receiver
worse. The second problem may be the radio itself.
