<s>
Airband	B-Algorithm
or	O
aircraft	B-Algorithm
band	I-Algorithm
is	O
the	O
name	O
for	O
a	O
group	O
of	O
frequencies	O
in	O
the	O
VHF	B-Algorithm
radio	B-Algorithm
spectrum	I-Algorithm
allocated	O
to	O
radio	O
communication	O
in	O
civil	O
aviation	O
,	O
sometimes	O
also	O
referred	O
to	O
as	O
VHF	B-Algorithm
,	O
or	O
phonetically	O
as	O
"	O
Victor	O
"	O
.	O
</s>
<s>
Different	O
sections	O
of	O
the	O
band	O
are	O
used	O
for	O
radionavigational	O
aids	O
and	O
air	B-Application
traffic	I-Application
control	I-Application
.	O
</s>
<s>
In	O
most	O
countries	O
a	O
license	O
to	O
operate	O
airband	B-Algorithm
equipment	O
is	O
required	O
and	O
the	O
operator	O
is	O
tested	O
on	O
competency	O
in	O
procedures	O
,	O
language	O
and	O
the	O
use	O
of	O
the	O
phonetic	O
alphabet	O
.	O
</s>
<s>
The	O
VHF	B-Algorithm
airband	B-Algorithm
uses	O
the	O
frequencies	O
between	O
108	O
and	O
137MHz	O
.	O
</s>
<s>
These	O
are	O
reserved	O
for	O
navigational	O
aids	O
such	O
as	O
VOR	B-Device
beacons	B-Protocol
,	O
and	O
precision	O
approach	O
systems	O
such	O
as	O
ILS	O
localizers	O
.	O
</s>
<s>
,	O
most	O
countries	O
divide	O
the	O
upper	O
19MHz	O
into	O
760	O
channels	O
for	O
amplitude	B-Device
modulation	I-Device
voice	O
transmissions	O
,	O
on	O
frequencies	O
from	O
118	O
to	O
136.975MHz	O
,	O
in	O
steps	O
of	O
25kHz	O
.	O
</s>
<s>
Aeronautical	O
voice	O
communication	O
is	O
also	O
conducted	O
in	O
other	O
frequency	O
bands	O
,	O
including	O
satellite	O
voice	O
on	O
Inmarsat	O
,	O
Globalstar	O
or	O
Iridium	O
,	O
and	O
high	B-Algorithm
frequency	I-Algorithm
voice	O
.	O
</s>
<s>
Military	O
aircraft	O
also	O
use	O
a	O
dedicated	O
UHF-AM	O
band	O
from	O
225.0	O
to	O
399.95MHz	O
for	O
air-to-air	O
and	O
air-to-ground	O
,	O
including	O
air	B-Application
traffic	I-Application
control	I-Application
communication	O
.	O
</s>
<s>
Non-directional	O
beacons	B-Protocol
(	O
NDB	O
)	O
s	O
operate	O
on	O
low	B-Algorithm
frequency	I-Algorithm
and	O
medium	B-Algorithm
frequency	I-Algorithm
bands	O
190	O
–	O
415kHz	O
and	O
510	O
–	O
535kHz	O
.	O
</s>
<s>
The	O
instrument	O
landing	O
system	O
(	O
ILS	O
)	O
glide	O
path	O
operates	O
in	O
the	O
UHF	O
range	O
of	O
329.3	O
–	O
335.0MHz	O
with	O
marker	O
beacons	B-Protocol
at	O
75MHz	O
.	O
</s>
<s>
Channel	O
spacing	O
for	O
voice	O
communication	O
on	O
the	O
airband	B-Algorithm
was	O
originally	O
200kHz	O
until	O
1947	O
,	O
providing	O
70	O
channels	O
from	O
118	O
to	O
132MHz	O
.	O
</s>
<s>
Increasing	O
air	B-Application
traffic	I-Application
congestion	O
has	O
led	O
to	O
further	O
subdivision	O
into	O
narrow-band	O
8.33kHz	O
channels	O
in	O
the	O
ICAO	O
European	O
region	O
;	O
since	O
2007	O
,	O
all	O
aircraft	O
flying	O
above	O
FL195	O
are	O
required	O
to	O
have	O
communication	O
equipment	O
for	O
this	O
channel	O
spacing	O
.	O
</s>
<s>
Aircraft	O
communications	O
radio	O
operations	O
worldwide	O
use	O
amplitude	B-Device
modulation	I-Device
,	O
predominantly	O
A3E	O
double	O
sideband	O
with	O
full	O
carrier	O
on	O
VHF	B-Algorithm
and	O
UHF	O
,	O
and	O
J3E	B-Device
single	O
sideband	O
with	O
suppressed	O
carrier	O
on	O
HF	O
.	O
</s>
<s>
Even	O
if	O
both	O
transmissions	O
are	O
received	O
with	O
identical	O
signal	O
strength	O
,	O
a	O
heterodyne	B-Algorithm
will	O
be	O
heard	O
where	O
no	O
such	O
indication	O
of	O
blockage	O
would	O
be	O
evident	O
in	O
an	O
FM	O
system	O
.	O
</s>
<s>
The	O
audio	O
quality	O
in	O
the	O
airband	B-Algorithm
is	O
limited	O
by	O
the	O
RF	B-Algorithm
bandwidth	I-Algorithm
used	O
.	O
</s>
<s>
In	O
the	O
newer	O
channel	O
spacing	O
scheme	O
,	O
the	O
largest	O
bandwidth	B-Algorithm
of	O
an	O
airband	B-Algorithm
channel	O
is	O
limited	O
to	O
8.33kHz	O
,	O
so	O
the	O
highest	O
possible	O
audio	O
frequency	O
is	O
4.166kHz	O
.	O
</s>
<s>
However	O
,	O
most	O
airband	B-Algorithm
voice	O
transmissions	O
never	O
actually	O
reach	O
these	O
limits	O
.	O
</s>
<s>
Usually	O
,	O
the	O
whole	O
transmission	O
is	O
contained	O
within	O
a	O
6kHz	O
to	O
8kHz	O
bandwidth	B-Algorithm
,	O
corresponding	O
to	O
an	O
upper	O
audio	O
frequency	O
of	O
3kHz	O
to	O
4kHz	O
.	O
</s>
<s>
Different	O
aircraft	O
,	O
control	O
towers	O
and	O
other	O
users	O
transmit	O
with	O
different	O
bandwidths	B-Algorithm
and	O
audio	O
characteristics	O
.	O
</s>
<s>
A	O
switch	O
to	O
digital	O
radios	O
has	O
been	O
contemplated	O
,	O
as	O
this	O
would	O
greatly	O
increase	O
capacity	O
by	O
reducing	O
the	O
bandwidth	B-Algorithm
required	O
to	O
transmit	O
speech	O
.	O
</s>
<s>
It	O
is	O
illegal	O
in	O
most	O
countries	O
to	O
transmit	O
on	O
the	O
airband	B-Algorithm
frequencies	O
without	O
a	O
suitable	O
license	O
,	O
although	O
an	O
individual	O
license	O
may	O
not	O
be	O
required	O
,	O
for	O
instance	O
in	O
the	O
US	O
where	O
aircraft	O
stations	O
are	O
"	O
licensed	O
by	O
rule	O
"	O
.	O
</s>
<s>
Many	O
countries	O
 '	O
regulations	O
also	O
restrict	O
communications	O
in	O
the	O
airband	B-Algorithm
.	O
</s>
<s>
For	O
instance	O
,	O
in	O
Canada	O
,	O
airband	B-Algorithm
communications	O
are	O
limited	O
to	O
those	O
required	O
for	O
"	O
the	O
safety	O
and	O
navigation	O
of	O
an	O
aircraft	O
;	O
the	O
general	O
operation	O
of	O
the	O
aircraft	O
;	O
and	O
the	O
exchange	O
of	O
messages	O
on	O
behalf	O
of	O
the	O
public	O
.	O
</s>
<s>
Listening	O
to	O
airband	B-Algorithm
frequencies	O
without	O
a	O
license	O
is	O
also	O
an	O
offense	O
in	O
some	O
countries	O
.	O
</s>
<s>
Such	O
activity	O
has	O
been	O
the	O
subject	O
of	O
international	O
situations	O
between	O
governments	O
when	O
tourists	O
bring	O
airband	B-Algorithm
equipment	O
into	O
countries	O
which	O
ban	O
the	O
possession	O
and	O
use	O
of	O
such	O
equipment	O
.	O
</s>
