Very high frequency
Frequency range | 30 MHz |
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Wavelength range | 10 to 1 m |
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Very high frequency (VHF) is the
VHF radio waves propagate mainly by
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 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
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
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
Universal use
Certain subparts of the VHF band have the same use around the world. Some national uses are detailed below.
- 50–54 MHz: Amateur Radio 6-meter band.
- 108–118 MHz: Air navigation beacons Instrument Landing Systemlocalizer.
- 118–137 MHz: Airband for air traffic control, AM, 121.5 MHz is emergency frequency
- 144–146 MHz: Amateur Radio 2-meter band(Extends up to 148 MHz in some Regions).
- 156–174 MHz: VHF maritime mobile band for maritime two-way radioon ships.
By country
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
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
- 44–51, 54–68 MHz: Band I Television (channels 1–3)
- 87.5–108 MHz: Band II Radio
- 118–137 MHz: Airband for air traffic control, AM
- 144–148 MHz: Amateur radio 2-meter band
- 156–162.2 MHz: Marine radio
- 174–230 MHz: Band III Television (channels 4–11)
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
United Kingdom
British television originally used VHF
-adapted for the 405-line system in the late 1950s and early 1960s).British colour television was broadcast on
Unusually, the UK has an
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.[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
- 50.8–51 MHz: Radio-controlled aircraft (on ten fixed frequencies at 20 kHz spacing) with an FCC Amateur Radio Service license, flown under FCC Part 97, rule 97.215.[6]
- 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
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
87.5–87.9 MHz is a radio band which, in most of the world, is used for
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
Unlicensed operation
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
See also
- Marine VHF radio
- TV radio
- List of oldest radio stations
- Apex (radio band)
- FM broadcast band
- Moving image formats
- Polar mesosphere summer echoes
- Television channel frequencies
- Knife-edge effect
- VHF omnidirectional range
- High frequency
- Low frequency
- Extremely low frequency
- Ultra low frequency
Notes
- ^ The 42 MHz Segment is still in current use by the California Highway Patrol, New Jersey State Police, Tennessee Highway Patrol, and other state law enforcement agencies.
- railroad radios, issued to the railroad. For example, AAR 21 is 160.425 MHz and that is issued to Tennessee Valley Railroad Museum, as well as other railroads that want AAR Channel 21.
References
- ^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Archived from the original (PDF) on 31 October 2013. Retrieved 20 February 2013.
- ISBN 978-0471743682.
- ^ "Marine VHF radio". [[Australian Communications & Media Authority|]].
- ^ "Australian radiofrequency spectrum plan". Planning. Australian Communications & Media Authority.
- ^ "Going Digital - When is my area going digital?". goingdigital.co.nz. Ministry for Culture and Heritage. Archived from the original on 17 October 2011. Retrieved 20 October 2011.
- ^ "Electronic Code of Federal Regulations (ECFR)". Archived from the original on 2021-01-26. Retrieved 2019-03-05.
- ^ a b Canadian Table of Frequency Allocations 9 kHz – 275 GHz (2005 (revised February 2007) ed.). Industry Canada. February 2007. pp. 29–30.
- ^ "Cable TV Channel Frequencies". www.jneuhaus.com. Archived from the original on 23 August 2017. Retrieved 27 April 2018.
- ^ "What Ever Happened to Channel 1?". tech-notes.tv. Tech Notes. Table 1. Archived from the original on 17 March 2017. Retrieved 27 April 2018.
- ^ "Change to the law to allow the use of low power FM transmitters for MP3 players". Ofcom. 23 November 2006. Archived from the original on 7 August 2011. Retrieved 2 October 2012.