<s>
High	B-Algorithm
frequency	I-Algorithm
(	O
HF	O
)	O
is	O
the	O
ITU	O
designation	O
for	O
the	O
range	O
of	O
radio	O
frequency	O
electromagnetic	O
waves	O
(	O
radio	O
waves	O
)	O
between	O
3	O
and	O
30	O
megahertz	O
(	O
MHz	O
)	O
.	O
</s>
<s>
Frequencies	O
immediately	O
below	O
HF	O
are	O
denoted	O
medium	B-Algorithm
frequency	I-Algorithm
(	O
MF	O
)	O
,	O
while	O
the	O
next	O
band	O
of	O
higher	O
frequencies	O
is	O
known	O
as	O
the	O
very	B-Algorithm
high	I-Algorithm
frequency	I-Algorithm
(	O
VHF	B-Algorithm
)	O
band	O
.	O
</s>
<s>
The	O
band	O
is	O
used	O
by	O
international	O
shortwave	O
broadcasting	O
stations	O
(	O
3.95	O
–	O
25.82MHz	O
)	O
,	O
aviation	O
communication	O
,	O
government	O
time	O
stations	O
,	O
weather	O
stations	O
,	O
amateur	O
radio	O
and	O
citizens	B-Application
band	I-Application
services	O
,	O
among	O
other	O
uses	O
.	O
</s>
<s>
By	O
this	O
method	O
HF	B-Algorithm
radio	I-Algorithm
waves	O
can	O
travel	O
beyond	O
the	O
horizon	O
,	O
around	O
the	O
curve	O
of	O
the	O
Earth	O
,	O
and	O
can	O
be	O
received	O
at	O
intercontinental	O
distances	O
.	O
</s>
<s>
This	O
absorption	O
is	O
stronger	O
at	O
low	O
frequencies	O
and	O
is	O
also	O
stronger	O
with	O
increased	O
solar	B-Application
activity	I-Application
(	O
for	O
example	O
in	O
daylight	O
)	O
;	O
total	O
absorption	O
often	O
occurs	O
at	O
frequencies	O
below	O
5MHz	O
during	O
the	O
daytime	O
.	O
</s>
<s>
The	O
result	O
of	O
these	O
two	O
factors	O
is	O
that	O
the	O
usable	O
spectrum	O
shifts	O
towards	O
the	O
lower	O
frequencies	O
and	O
into	O
the	O
Medium	B-Algorithm
Frequency	I-Algorithm
(	O
MF	O
)	O
range	O
during	O
winter	O
nights	O
,	O
while	O
on	O
a	O
day	O
in	O
full	O
summer	O
the	O
higher	O
frequencies	O
tend	O
to	O
be	O
more	O
usable	O
,	O
often	O
into	O
the	O
lower	O
VHF	B-Algorithm
range	O
.	O
</s>
<s>
When	O
a	O
transcontinental	O
or	O
worldwide	O
path	O
is	O
open	O
on	O
a	O
particular	O
frequency	O
,	O
digital	O
,	O
SSB	B-Device
and	O
Morse	O
code	O
communication	O
is	O
possible	O
using	O
surprisingly	O
low	O
transmission	O
powers	O
,	O
often	O
of	O
the	O
order	O
of	O
milliwatts	O
,	O
provided	O
suitable	O
antennas	O
are	O
in	O
use	O
at	O
both	O
ends	O
and	O
that	O
there	O
is	O
little	O
or	O
no	O
man-made	O
or	O
natural	O
interference	O
.	O
</s>
<s>
The	O
main	O
uses	O
of	O
the	O
high	B-Algorithm
frequency	I-Algorithm
spectrum	O
are	O
:	O
</s>
<s>
The	O
high	B-Algorithm
frequency	I-Algorithm
band	O
is	O
very	O
popular	O
with	O
amateur	O
radio	O
operators	O
,	O
who	O
can	O
take	O
advantage	O
of	O
direct	O
,	O
long-distance	O
(	O
often	O
inter-continental	O
)	O
communications	O
and	O
the	O
"	O
thrill	O
factor	O
"	O
resulting	O
from	O
making	O
contacts	O
in	O
variable	O
conditions	O
.	O
</s>
<s>
International	O
shortwave	O
broadcasting	O
utilizes	O
this	O
set	O
of	O
frequencies	O
,	O
as	O
well	O
as	O
a	O
seemingly	O
declining	O
number	O
of	O
"	O
utility	O
"	O
users	O
(	O
marine	O
,	O
aviation	O
,	O
military	O
,	O
and	O
diplomatic	O
interests	O
)	O
,	O
who	O
have	O
,	O
in	O
recent	O
years	O
,	O
been	O
swayed	O
over	O
to	O
less	O
volatile	O
means	O
of	O
communication	O
(	O
for	O
example	O
,	O
via	O
satellites	B-Application
)	O
,	O
but	O
may	O
maintain	O
HF	O
stations	O
after	O
switch-over	O
for	O
back-up	O
purposes	O
.	O
</s>
<s>
However	O
,	O
the	O
development	O
of	O
Automatic	B-Device
Link	I-Device
Establishment	I-Device
technology	O
based	O
on	O
MIL-STD-188-141	O
for	O
automated	O
connectivity	O
and	O
frequency	O
selection	O
,	O
along	O
with	O
the	O
high	O
costs	O
of	O
satellite	B-Application
usage	O
,	O
have	O
led	O
to	O
a	O
renaissance	O
in	O
HF	O
usage	O
in	O
government	O
networks	O
.	O
</s>
<s>
Other	O
standards	O
development	O
such	O
as	O
STANAG	O
5066	O
provides	O
for	O
error	O
free	O
data	O
communications	O
through	O
the	O
use	O
of	O
ARQ	B-Error_Name
protocols	I-Error_Name
.	O
</s>
<s>
Some	O
modes	O
of	O
communication	O
,	O
such	O
as	O
continuous	O
wave	O
Morse	O
code	O
transmissions	O
(	O
especially	O
by	O
amateur	O
radio	O
operators	O
)	O
and	O
single	B-Device
sideband	I-Device
voice	O
transmissions	O
are	O
more	O
common	O
in	O
the	O
HF	O
range	O
than	O
on	O
other	O
frequencies	O
,	O
because	O
of	O
their	O
bandwidth-conserving	O
nature	O
,	O
but	O
broadband	O
modes	O
,	O
such	O
as	O
TV	O
transmissions	O
,	O
are	O
generally	O
prohibited	O
by	O
HF	O
's	O
relatively	O
small	O
chunk	O
of	O
electromagnetic	O
spectrum	O
space	O
.	O
</s>
<s>
The	O
upper	O
section	O
of	O
HF	O
(	O
26.5-30MHz	O
)	O
shares	O
many	O
characteristics	O
with	O
the	O
lower	O
part	O
of	O
VHF	B-Algorithm
.	O
</s>
<s>
These	O
include	O
CB	B-Application
radios	I-Application
around	O
27MHz	O
,	O
studio-to-transmitter	O
(	O
STL	O
)	O
radio	O
links	O
,	O
radio	O
control	O
devices	O
for	O
models	O
and	O
radio	O
paging	O
transmitters	O
.	O
</s>
<s>
These	O
tags	O
are	O
commonly	O
known	O
as	O
HFID	O
's	O
or	O
HighFID	O
's	O
(	O
High-Frequency	B-Algorithm
Identification	O
)	O
.	O
</s>
