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ELECTROMAGNETIC-WAVE PROPAGATION
Electromagnetic waves of a SW broadcast are separated into sur-
face waves which are propagated along the surface of the earth
and space waves which are propagated upwards. Low frequency
waves (LW and MW) are surface waves, while high frequency
waves (SW) are bounced off the ionosphere which is located
100-300km above the earth surface. This layer is charged and
acts like a mirror toward electromagnetic waves. That is why
high frequency waves can be received over great distances.
On the other hand, the electromagnetic waves of higher fre-
quencies (VHF) protrude through the ionosphere and can only
be used for short distances.
The ionosphere is thought to have been made by the ultra-violet
rays of the sun, and consequently, the conditions of the ionos-
phere change from time to time due to the position of the sun.
Seasonal variations also occur. Since it is multilayered, the path
of propagation of electric waves is extremely complex; In parti-
cular, solar spots whose number changes every 11 years changes
affects the shape of the propagation. In receiving SW broadcast,
PRECAUTIONS
For your safety and to prevent damage to the set:
•
Do not connect the set to any AC outlet other than the type
supplying 120 volts.
•
Avoid cuts, scratches, or poor connections in the AC power
cord which may result in possible fire or electric shock
hazard. Also, excessive bending, pulling, or slicing of the
cord should be avoided.
•
Do not unplug the AC power cord by pulling on the cord. To
do so may cause permature failure or shock hazard.
•
Do not operate the set on AC power in a bathroom as a poten-
tial shock hazard may result.
-9-
one must keep all of the foregoing in mind. The best known SW
stations take all of the factors into consideration and change the
frequency from season to season or broadcast with two or more
different frequencies at the same time, so that the most suitable
reception can be achieved.
Broad-
casting
station
HELPFUL HINTS
Fig. 18
•
If the set is not used for a long time or is used only from an
AC power source, remove all the batteries to prevent poten-
tial damage due to possible battery leakage.
•
When the sound volume begins to lower, it is advisable to
replace all the batteries. with new ones before they are
completely discharged.
•
Do not subject the set to a temperature of over 60°C (140°F),
because characteristics of the internal parts may be adverse-
ly affected by heat. Especially, never leave the set in a car
exposed to direct sunlight for a long time with all the doors
and windows closed. The cabinet may become' deformed,
and deterioration of the performance may result.
•
Do not use benzine, thinner, or the like, or any abrasive
powder to clean the cabinet. Wipe it with soft cloth moistened
with a mild soap and water solution.
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