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Hi!
My name is Callinda Coyote!
When we turn on a radio,
invisible radio waves are intercepted by an antenna, amplified by
the receiver in the radio and converted to (invisible) sound waves.
A radio receiver is tuned to a specific frequency within a certain
band on the radio dial; for example, 850 (or 850 KHz) AM or 89.3 (89.3
MHz) FM. AM refers to Amplitude Modulation, FM to Frequency modulation.
These terms refer to the way the sound is put on the radio wave. But
are there other bands?
Yes, of course there are. AM
radio extends from 550-1600 kHz, FM radio from 88 MHz-108 MHz. TV
is from 52-88 MHz (channels 1-6), 174-216 MHz (channels 7-12) and
470-900 MHz (UHF). Microwave and satellite signals are of the order
of several GHz and infrared fiber-optic signals are of the order of
200-300 THz.
All the bands of radio waves (see chart on left)
are part of the electromagnetic spectrum, which includes infrared,
visible, X-, and gamma- radiation. Scientists graph the spectrum like
this:
Something very interesting happens
if you are patient enough and listen to a radio receiver tuned to
the VLF band of the spectrum. You may hear crunches and crackles,
similar to the sound of bacon frying. You are hearing Sferics, a term
that is shortened from atmospherics. Sferics are a type of radio noise
produced by lightning. If the strikes are close, perhaps within a
range of 0 to 50 miles, the noise is very strong. Sferics can interfere
with regular broadcast radio (AM through Short-wave) reception if
the strikes are close. Here is what sferics would look like when graphed
(time is on the x-axis, frequency is on the y-axis):
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