Electromagnetic
were
predicted
by
James
Clerk
Maxwell
in
his
1873
theory
of
electromagnetism
,
now
called
Maxwell's
equations
,
who
proposed
that
a
coupled
oscillating
electric
field
and
magnetic
field
could
through
space
as
a
wave
,
and
proposed
that
light
consisted
of
electromagnetic
waves
of
short
wavelength
.
On
November
11
,
1886
,
German
Heinrich
Hertz
,
attempting
to
confirm
Maxwell's
theory
,
first
observed
radio
waves
he
generated
using
a
primitive
spark
gap
transmitter
.
Experiments
by
Hertz
and
physicists
Jagadish
Chandra
Bose
,
Oliver
Lodge
,
Lord
Rayleigh
,
and
Augusto
Righi
,
among
others
,
showed
that
waves
like
light
demonstrated
reflection
,
refraction
,
diffraction
,
polarization
,
standing
waves
,
and
traveled
at
the
same
as
light
,
confirming
that
both
light
and
radio
waves
were
electromagnetic
waves
,
differing
only
in
frequency
.
In
1895
,
Guglielmo
Marconi
developed
the
first
radio
system
,
using
a
spark
gap
transmitter
to
send
Morse
over
long
distances
.
By
December
1901
,
he
had
transmitted
across
the
Atlantic
ocean
.
Karl
Ferdinand
Braun
invented
the
phased
array
antenna
in
1905
.
Three
antennas
are
arranged
to
transmit
a
directional
.
Marconi
and
Braun
shared
the
1909
Nobel
Prize
in
Physics
"
for
their
contributions
to
the
development
of
telegraphy
"
.
During
radio's
first
two
decades
,
called
the
radiotelegraphy
era
,
the
primitive
damped
wave
radio
transmitters
could
only
transmit
pulses
of
radio
waves
,
not
the
continuous
waves
which
were
needed
for
audio
modulation
,
so
radio
was
used
for
person
-
to
-
person
,
diplomatic
and
military
text
messaging
.
Starting
around
1908
industrial
countries
worldwide
networks
of
powerful
transoceanic
spark
transmitters
to
telegram
traffic
between
continents
and
communicate
with
their
colonies
and
naval
fleets
.
During
World
War
I
the
development
of
continuous
wave
radio
transmitters
and
rectifying
electrolytic
and
crystal
radio
receiver
detectors
amplitude
modulation
(
AM
)
radiotelephony
to
be
achieved
by
Reginald
Fessenden
and
others
,
allowing
sound
(
audio
)
to
be
transmitted
.
On
November
2
,
1920
,
the
first
commercial
radio
was
transmitted
by
Westinghouse
Electric
and
Manufacturing
Company
in
Pittsburgh
,
under
the
call
sign
KDKA
featuring
live
coverage
of
the
Harding
-
Cox
presidential
election
.
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