<s>
A	O
damped	B-Device
wave	I-Device
was	O
an	O
early	O
method	O
of	O
radio	O
transmission	O
produced	O
by	O
the	O
first	O
radio	O
transmitters	O
(	O
spark	O
gap	O
transmitters	O
)	O
which	O
consisted	O
of	O
a	O
series	O
of	O
damped	O
radio	O
waves	O
.	O
</s>
<s>
Information	O
was	O
carried	O
on	O
this	O
signal	O
by	O
telegraphy	O
,	O
turning	O
the	O
transmitter	O
on	O
and	O
off	O
(	O
on-off	B-Device
keying	I-Device
)	O
to	O
send	O
messages	O
in	O
Morse	O
code	O
.	O
</s>
<s>
Damped	B-Device
waves	I-Device
were	O
the	O
first	O
practical	O
means	O
of	O
radio	O
communication	O
,	O
used	O
during	O
the	O
wireless	O
telegraphy	O
era	O
which	O
ended	O
around	O
1920	O
.	O
</s>
<s>
Such	O
transmissions	O
have	O
a	O
wide	O
bandwidth	B-Algorithm
and	O
generate	O
electrical	O
"	O
noise	O
"	O
(	O
electromagnetic	O
interference	O
)	O
which	O
interferes	O
with	O
other	O
radio	O
transmissions	O
.	O
</s>
<s>
Because	O
of	O
their	O
potential	O
to	O
cause	O
interference	O
and	O
their	O
resulting	O
wasteful	O
use	O
of	O
radio	B-Algorithm
spectrum	I-Algorithm
resources	O
,	O
there	O
is	O
an	O
international	O
prohibition	O
against	O
the	O
use	O
of	O
class	O
B	O
damped	B-Device
wave	I-Device
radio	O
emissions	O
(	O
except	O
in	O
the	O
USA	O
under	O
Part	O
15	O
:	O
"	O
§	O
15.521	O
Technical	O
requirements	O
applicable	O
to	O
all	O
UWB	O
devices	O
.	O
</s>
<s>
(	O
i	O
)	O
The	O
prohibition	O
in	O
§	O
2.201(f )	O
and	O
15.5(d )	O
of	O
this	O
chapter	O
against	O
Class	O
B	O
(	O
damped	B-Device
wave	I-Device
)	O
emissions	O
does	O
not	O
apply	O
to	O
UWB	O
devices	O
operating	O
under	O
this	O
subpart	O
.	O
</s>
<s>
However	O
the	O
definition	O
of	O
"	O
damped	B-Device
waves	I-Device
"	O
in	O
these	O
regulations	O
is	O
unclear	O
when	O
applied	O
to	O
modern	O
technology	O
,	O
and	O
recently	O
there	O
have	O
been	O
moves	O
to	O
amend	O
this	O
prohibition	O
to	O
exempt	O
emerging	O
radio	O
technologies	O
such	O
as	O
ultra-wideband	O
transmission	O
systems	O
.	O
</s>
