Very high frequency


Very high frequency is the ITU designation for the range of radio frequency electromagnetic waves from 30 to 300 megahertz, with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF are denoted high frequency, and the next higher frequencies are known as ultra high frequency.
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. Common uses for radio waves in the VHF band are Digital Audio Broadcasting and FM radio broadcasting, television broadcasting, two-way land mobile radio systems, 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 work at distances of 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

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. 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 by the atmosphere they can travel somewhat beyond the visual horizon out to about 160 km. 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 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 and ships. 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

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 is:
  • distance in nautical miles = where is the height of the antenna in feet
  • distance in kilometers = where is the height of the antenna in meters.
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.

Antennas

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 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

Certain subparts of the VHF band have the same use around the world. Some national uses are detailed below.

Australia

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 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 as per its long-distance reachability comparing UHF frequencies.
Example allocation of VHF–UHF frequencies:
  • 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 73: 315-325 MHz

    New Zealand

  • 44-51, 54-68 MHz: Band I Television
  • 87.5-108 MHz: Band II Radio
  • 118-137 MHz: Airband for air traffic control, AM
  • *108-117.975 MHz: Air navigation beacons VOR and ILS
  • *121.5 MHz is an emergency frequency
  • 144-148 MHz: Amateur radio 2-meter band
  • 156-162.2 MHz: Marine radio
  • 174-230 MHz: Band III Television
Until 2013, the four main free-to-air TV stations in New Zealand used the VHF television bands 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 utilising the Freeview service.
Refer to Australasian television frequencies for more information.

United Kingdom

British television originally used VHF band I and band III. Television on VHF was in black and white with 405-line format.
British colour television was broadcast on UHF, beginning in the late 1960s. From then on, TV was broadcast on both VHF and UHF, with the exception of BBC2. 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

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.
  • 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 before it was moved to 88-108 MHz.
  • 50-54 MHz: Amateur radio 6-meter band
  • *50.8-51 MHz: Radio-controlled aircraft with an FCC amateur radio Service license, flown under FCC Part 97, rule 97.215.
  • 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
  • *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
  • 87.5-108 MHz: FM radio broadcasting
  • 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
  • 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, and other 2-way land mobile, FM
  • 156-158 MHz VHF Marine Radio
  • *156.8 MHz is the maritime emergency and contact frequency.
  • 159.81-161.565 MHz railways
  • *159.81-160.2 are railroads in Canada only and are 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
  • *174-216 MHz: professional wireless microphones
  • *216-222 MHz: land mobile, fixed, maritime mobile,
  • *222-225 MHz: 1.25 meters amateur radio
  • 225 MHz and above : Military aircraft radio, 243 MHz is an emergency frequency AM, including HAVE QUICK, dGPS RTCM-104
Cable television, though not transmitted aerially, uses a spectrum of frequencies overlapping VHF.