Electromagnetic wave range of 30-300 MHz
Very high frequency
Frequency range
| 30
MHz
to 300
MHz
|
---|
Wavelength range
| 10 to 1 m
|
---|
Very high frequency
(
VHF
) is the
ITU
designation
[1]
for the range of
radio frequency
electromagnetic waves
(
radio waves
) from 30 to 300
megahertz
(MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF are denoted
high frequency
(HF), and the next higher frequencies are known as
ultra high frequency
(UHF).
VHF radio waves propagate mainly by
line-of-sight
, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the
visual horizon
out to about 160 km (100 miles). Common uses for radio waves in the VHF band are
Digital Audio Broadcasting
(DAB) and
FM radio
broadcasting,
television broadcasting
,
two-way
land mobile radio systems
(emergency, business, private use and military), long range data communication up to several tens of kilometers with
radio modems
,
amateur radio
, and
marine communications
.
Air traffic control
communications and air navigation systems (e.g.
VOR
and
ILS
) work at distances of 100 kilometres (62 mi) or more to aircraft at cruising altitude.
In the Americas and many other parts of the world, VHF
Band I
was used for the transmission of
analog television
. As part of the worldwide
transition to digital terrestrial television
most countries require broadcasters to air television in the VHF range using digital, rather than analog encoding.
Propagation characteristics
[
edit
]
Radio waves in the VHF band propagate mainly by
line-of-sight
and ground-bounce paths; unlike in the
HF
band there is only some reflection at lower frequencies from the
ionosphere
(
skywave
propagation).
[2]
They do not follow the contour of the Earth as
ground waves
and so are blocked by hills and mountains, although because they are weakly refracted (bent) by the atmosphere they can travel somewhat beyond the
visual horizon
out to about 160 km (100 miles). They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause
multipath propagation
, which can interfere with television reception. Atmospheric
radio noise
and interference (
RFI
) from electrical equipment is less of a problem in this and higher frequency bands than at lower frequencies. The VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for
two-way
land mobile radio systems
, such as
walkie-talkies
, and
two way radio
communication with aircraft (
Airband
) and ships (
marine radio
). Occasionally, when conditions are right, VHF waves can travel long distances by
tropospheric ducting
due to refraction by temperature gradients in the atmosphere.
Line-of-sight calculation
[
edit
]
VHF transmission range is a function of transmitter power, receiver sensitivity, and distance to the horizon, since VHF signals propagate under normal conditions as a near
line-of-sight
phenomenon. The distance to the
radio horizon
is slightly extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere.
An approximation to calculate the line-of-sight horizon distance (on Earth) is:
- distance in nautical miles =
where
is the height of the antenna in feet
[
citation needed
]
- distance in kilometers =
where
is the height of the antenna in meters.
[
citation needed
]
These approximations are only valid for antennas at heights that are small compared to the radius of the Earth. They may not necessarily be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves.
In engineered communications systems, more complex calculations are required to assess the probable coverage area of a proposed transmitter station.
[
citation needed
]
Antennas
[
edit
]
VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a
quarter wave whip antenna
at VHF frequencies is 25 cm to 2.5 meter (10 inches to 8 feet) long. So the VHF and UHF wavelengths are used for
two-way radios
in vehicles, aircraft, and handheld
transceivers
and
walkie-talkies
. Portable radios usually use
whips
or
rubber ducky antennas
, while base stations usually use larger fiberglass whips or
collinear arrays
of vertical dipoles.
For directional antennas, the
Yagi antenna
is the most widely used as a
high gain
or "beam" antenna. For television reception, the Yagi is used, as well as the
log-periodic antenna
due to its wider bandwidth.
Helical
and
turnstile antennas
are used for
satellite communication
since they employ
circular polarization
. For even higher gain, multiple Yagis or helicals can be mounted together to make
array antennas
. Vertical
collinear arrays
of dipoles can be used to make high gain
omnidirectional antennas
, in which more of the antenna's power is radiated in horizontal directions. Television and FM broadcasting stations use collinear arrays of specialized dipole antennas such as
batwing antennas
.
Universal use
[
edit
]
Certain subparts of the VHF band have the same use around the world. Some national uses are detailed below.
By country
[
edit
]
Australia
[
edit
]
The VHF TV band in Australia was originally allocated channels 1 to 10-with channels 2, 7 and 9 assigned for the initial services in
Sydney
and
Melbourne
, and later the same channels were assigned in
Brisbane
,
Adelaide
and
Perth
. Other capital cities and regional areas used a combination of these and other frequencies as available. The initial commercial services in
Hobart
and
Darwin
were respectively allocated channels 6 and 8 rather than 7 or 9.
By the early 1960s it became apparent that the 10 VHF channels were insufficient to support the growth of television services. This was rectified by the addition of three additional frequencies-channels 0, 5A and 11. Older television sets using rotary dial tuners required adjustment to receive these new channels. Most TVs of that era were not equipped to receive these broadcasts, and so were modified at the owners' expense to be able to tune into these bands; otherwise the owner had to buy a new TV.
Several TV stations were allocated to VHF channels 3, 4 and 5, which were within the FM radio bands although not yet used for that purpose. A couple of notable examples were
NBN-3
Newcastle
,
WIN-4
Wollongong
and
ABC
Newcastle
on channel 5. While some Channel 5 stations were moved to 5A in the 1970s and 80s, beginning in the 1990s, the
Australian Broadcasting Authority
began a process to move these stations to
UHF
bands to free up valuable VHF spectrum for its original purpose of FM radio. In addition, by 1985 the federal government decided new TV stations are to be broadcast on the UHF band.
Two new VHF channels, 9A and 12, have since been made available and are being used primarily for digital services (e.g.
ABC
in capital cities) but also for some new analogue services in regional areas. Because channel 9A is not used for television services in or near Sydney, Melbourne, Brisbane, Adelaide or Perth,
digital radio
in those cities are broadcast on DAB frequencies blocks 9A, 9B and 9C.
VHF radio is also used for marine Radio
[3]
as per its long-distance reachability comparing UHF frequencies.
Example allocation of VHF?UHF frequencies:
[4]
- Radionavigation 60: 84–86 MHz
- Fixed Maritime Mobile: 130–135.7 MHz
- Fixed Aeronautical radio navigation: 160–190 MHz
- Broadcasting Aeronautical Radionavigation: 255–283.5 MHz
- Aeronautical Radionavigation AUS 49 / Maritime Radionavigation (radiobeacons) 73: 315–325 MHz
New Zealand
[
edit
]
Until 2013, the four main free-to-air TV stations in
New Zealand
used the VHF television bands (
Band I
and
Band III
) to transmit to New Zealand households. Other stations, including a variety of pay and regional free-to-air stations, were forced to broadcast in the
UHF
band, since the VHF band had been very overloaded with four stations sharing a very small frequency band, which was so overcrowded that one or more channels would not be available in some smaller towns.
However,
at the end of 2013
, all television channels stopped broadcasting on the VHF bands, as New Zealand moved to digital television broadcasting, requiring all stations to either broadcast on UHF or satellite (where UHF was unavailable) utilising the
Freeview
service.
[5]
Refer to
Australasian television frequencies
for more information.
United Kingdom
[
edit
]
British television originally used VHF
band I
and
band III
. Television on VHF was in black and white with
405-line
format (although there were experiments with all three colour systems-
NTSC
,
PAL
, and
SECAM
-adapted for the 405-line system in the late 1950s and early 1960s).
British colour television was broadcast on
UHF
(channels 21?69), beginning in the late 1960s. From then on, TV was broadcast on both VHF and UHF (VHF being a monochromatic downconversion from the 625-line colour signal), with the exception of
BBC2
(which had always broadcast solely on UHF). The last British VHF TV transmitters closed down on January 3, 1985. VHF
band III
is now used in the UK for
digital audio broadcasting
, and VHF
band II
is used for
FM radio
, as it is in most of the world.
Unusually, the UK has an
amateur radio
allocation at
4 metres
, 70?70.5 MHz.
United States and Canada
[
edit
]
Frequency assignments between US and Canadian users are closely coordinated since much of the Canadian population is within VHF radio range of the US border. Certain discrete frequencies are reserved for
radio astronomy
.
The general services in the VHF band are:
- 30–49.6 MHz: Licensed 2-way land mobile communication, with various sub-bands.
[a]
- 30–88 MHz: Military VHF
FM
, including
SINCGARS
- 43–50 MHz:
Cordless telephones
, 49 MHz FM walkie-talkies and radio controlled toys, and mixed 2-way mobile communication. The FM broadcast band originally operated here (42–50 MHz) before it was moved to 88–108 MHz.
- 50–54 MHz:
Amateur radio
6-meter band
- 54–88 MHz, known as "
Band I
" internationally; some DTV stations will appear here. See
Pan-American television frequencies
.
- 54–72 MHz
TV
channels 2–4 (VHF-Lo)
- 72–76 MHz: Radio controlled models, industrial remote control, and other devices.
Model aircraft
operate on 72 MHz while surface models operate on 75 MHz in the US and Canada, air navigation beacons 74.8–75.2 MHz.
- 76–88 MHz TV channels 5–6 (VHF-Lo)
- 87.5–108 MHz:
FM radio
broadcasting (87.9–91.9 non-commercial, 92–108 commercial in the United States) (known as "
Band II
" internationally)
- 108–118 MHz: Air navigation beacons
VOR
- 118–137 MHz:
Airband
for
air traffic control
,
AM
- 121.5 MHz is an emergency frequency
- 137–138 MHz Space research, space operations, meteorological satellite
[7]
- 138–144 MHz: Land mobile, auxiliary civil services, satellite, space research, and other miscellaneous services
- 144–148 MHz:
Amateur radio
2-meter band
- 148–150 MHz: Land mobile, fixed, satellite
- 150–156 MHz: "VHF
business band
", public safety, the unlicensed
Multi-Use Radio Service
(MURS), and other 2-way land mobile, FM
- 156–158 MHz
VHF Marine Radio
- 156.8 MHz (Channel 16) is the maritime emergency and contact frequency.
- 159.81-161.565 MHz railways
[b]
- 159.81–160.2 are railroads in Canada only and is used by trucking companies in the U.S.
- 160.6–162 Wireless microphones and TV/FM broadcast remote pickup
- 162.4–162.55:
NOAA Weather Stations
, narrowband FM, Weatheradio Canada Stations
- 174–240 MHz, known as "
Band III
" internationally. A number of DTV channels have begun broadcasting here, especially many of the stations which were assigned to these channels for previous analog operation.
- 174–216 MHz television channels 7–13 (VHF-Hi)
- 174–216 MHz: professional wireless microphones (low power, certain exact frequencies only)
- 216–222 MHz: land mobile, fixed, maritime mobile,
[7]
- 222–225 MHz:
1.25 meters
(US) (Canada 219–220, 222–225 MHz)
amateur radio
- 225 MHz and above (UHF): Military aircraft radio, 243 MHz is an emergency frequency (225–400 MHz) AM, including
HAVE QUICK
, dGPS RTCM-104
Cable television
, though not transmitted aerially, uses a spectrum of frequencies overlapping VHF.
[8]
VHF television
[
edit
]
The U.S.
FCC
allocated television broadcasting to a channelized roster as early as 1938 with 19 channels. That changed three more times: in 1940 when Channel 19 was deleted and several channels changed frequencies, then in 1946 with television going from 18 channels to 13 channels, again with different frequencies, and finally in 1948 with the removal of
Channel 1
(analog channels 2?13 remain as they were, even on
cable television
).
[9]
Channels 14?19 later appeared on the UHF band, while channel 1 remains unused.
87.5–87.9 MHz
[
edit
]
87.5–87.9 MHz is a radio band which, in most of the world, is used for
FM broadcasting
. In
North America
, however, this bandwidth is allocated to VHF television channel 6 (82–88 MHz). The analog audio for TV channel 6 is broadcast at 87.75 MHz (adjustable down to 87.74). Several stations, known as
Frankenstations
, most notably those joining the
Pulse 87
franchise, have operated on this frequency as radio stations, though they use television licenses. As a result, FM radio receivers such as those found in automobiles which are designed to tune into this frequency range could receive the audio for analog-mode programming on the local TV channel 6 while in North America. The practice largely ended with the
DTV transition
in 2009, although some still exist.
The FM broadcast channel at 87.9 MHz is normally off-limits for FM audio broadcasting; it is reserved for displaced class D stations which have no other frequencies in the normal 88.1–107.9 MHz subband to move to. So far, only two stations have qualified to operate on 87.9 MHz: 10–watt
KSFH
in
Mountain View, California
and 34–watt translator
K200AA
in
Sun Valley, Nevada
.
Unlicensed operation
[
edit
]
In some countries, particularly the United States and Canada, limited low-power license-free operation is available in the FM broadcast band for purposes such as
micro-broadcasting
and sending output from
CD
or digital media players to radios without auxiliary-in jacks, though this is illegal in some other countries. This practice was legalised in the United Kingdom on 8 December 2006.
[10]
See also
[
edit
]
Notes
[
edit
]
References
[
edit
]
Broadcast bands with Roman numeral designations
|
---|
VHF
| |
---|
UHF
| |
---|
SHF
| |
---|
|
---|
ELF
3 Hz/100 Mm
30 Hz/10 Mm
|
SLF
30 Hz/10 Mm
300 Hz/1 Mm
|
ULF
300 Hz/1 Mm
3 kHz/100 km
|
VLF
3 kHz/100 km
30 kHz/10 km
|
LF
30 kHz/10 km
300 kHz/1 km
|
MF
300 kHz/1 km
3 MHz/100 m
|
HF
3 MHz/100 m
30 MHz/10 m
|
VHF
30 MHz/10 m
300 MHz/1 m
|
UHF
300 MHz/1 m
3 GHz/100 mm
|
SHF
3 GHz/100 mm
30 GHz/10 mm
|
EHF
30 GHz/10 mm
300 GHz/1 mm
|
THF
300 GHz/1 mm
3 THz/0.1 mm
|
|
|
|
---|
Terrestrial
| |
---|
Satellite
| |
---|
Codecs
| |
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Subcarrier
signals
| |
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Related topics
|
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Technical (audio)
| |
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Technical (
AM stereo
formats)
| |
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Technical (emission)
| |
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Cultural
| |
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|
|