Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Vhf shopping experience:
1. Compare - without doubt the biggest advantage that the Vhf offers shoppers today is the ability to compare thousands of Vhf at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Vhf? Wrong! If the Vhf is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Vhf then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Vhf? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Vhf and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Vhf wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Vhf then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Vhf site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Vhf, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Vhf, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
{| align="right" border="0" class="wikitable"|-!
very high frequency (VHF)] to 1 m|}
Very high frequency (VHF) is the radio frequency range from 30
megahertz to 300 megahertz. It is also known as the
meter band or
meter wave as the wavelengths range from ten to one
meters. Frequencies immediately below VHF are denoted
High frequency, and the next higher frequencies are known as
Ultra high frequency (UHF).
Common uses for VHF are FM radio broadcast at 88–108 MHz and television broadcast (together with ultra high frequency). VHF is also commonly used for terrestrial navigation systems (
VHF omnidirectional range in particular), marine communications, and aircraft communications.
VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than low frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less bothered by buildings and other less substantial objects than higher frequencies.
Two unusual propagation conditions can allow much farther range than normal. The first, tropospheric ducting, can occur in front of and parallel to an advancing cold weather front, especially if there is a marked difference in humidities between the cold and warm air masses. A duct can form approximately 150 miles (240 km.) in advance of the cold front, much like a ventilation duct in a building, and VHF radio frequencies can travel along inside the duct, bending or refracting, for hundreds of miles. For example, a 50 watt Amateur FM transmitter at 146 MHz can talk from Chicago, to
Joplin, Missouri, directly, and to Austin, Texas, through a repeater. In a July 2006 incident, a
NOAA Weather Radio transmitter in north central Wisconsin was blocking out local transmitters in west central Michigan, quite far out of its normal range. The second type, much more rare, is called Sporadic-E, referring to the E-layer of the ionosphere. A sunspot eruption can pelt the Earth's upper atmosphere with charged particles, which may allow the formation of an ionized "patch" dense enough to reflect back VHF frequencies the same way HF frequencies are usually reflected (skywave). For example,
KMID (54–60 MHz) from
Midland, Texas was seen in near
Chicago, pushing out Chicago's own WBBM-TV. These patches may last for seconds, or extend into hours. FM stations from
Miami, Florida, Florida; New Orleans, Louisiana; Houston, Texas and even Mexico were heard for hours in central Illinois during one such event. Mid summer 2006 central
Iowa stations were heard in
Columbus, NE and blocking out
Omaha radio and TV stations for several days.
It was also easier to construct efficient transmitters, receivers, and
antennas for it in the earlier days of radio, as compared to UHF. In most countries, the VHF spectrum is used for broadcast audio and television, as well as commercial two-way radios (such as those operated by taxis and police), marine two-way audio communications, and aircraft radios.
The large technically and commercially valuable slice of the VHF spectrum taken up by television transmission has attracted the attention of many companies and governments recently, with the development of more efficient digital television broadcasting standards. In some countries much of this spectrum will likely become available (probably for sale) in the next decade or so (currently scheduled for 2008 in the United States).
Line of Sight Formula
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 Line-of-sight propagation phenomenon.
An approximation to calculate the line-of-sight horizon distance is:
- distance in miles = \sqrt{1.5 \times A_f} where A_f is the height of the antenna in feet
- distance in kilometres = \sqrt{12.7 \times A_m} where A_m is the height of the antenna in metres
Australia
The VHF TV band in Australia was originally allocated channels 1 to 10 - with the 2, 7 and 9 frequencies assigned for the initial services in Sydney and Melbourne, and later the same frequencies were assigned in Brisbane, Adelaide and Perth. Other capital cities and regional areas used a combination of these and other frequencies as available.
By the early
1960s it was apparent that the 10-channel spectrum was not going to be sufficient 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 required adjustment to enable tuning to the new frequencies.
Several TV stations were allocated to VHF channels 3, 4 and 5A, which were within the FM radio bands although not yet used for that purpose. A couple of notable examples were
NBN Television Newcastle, New South Wales,
WIN-4 Wollongong, New South Wales and Australian Broadcasting Corporation
Illawarra on channel 5A. 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. Beginning in the
1990s, the Australian Broadcasting Authority began a process to move these stations to Ultra high frequency 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 frequencies, 9A and 12, have since been made available and are being used primarily for digital services (eg.
Australian Broadcasting Corporation in capital cities) but also for some new analogue services in regional areas.
New Zealand
- 44–51, 54–68 MHz: Band I Television (channels 1–3)
- 87.5–108 MHz: Band II Radio
- 174–230 MHz: Band III Television (channels 4–11)
In
New Zealand, the four main Free-to-Air TV stations still use the VHF Television bands (Band I and Band III) to transmit their programmes to New Zealand households. Other stations, including a variety of pay and regional free-to-air stations, broadcast their programmes using the
Ultra high frequency band, since the VHF band is very overloaded with four stations sharing a very small frequency band. In some areas, the band is so overcrowded, that the
C4 (TV channel) is not available.
United Kingdom
British television originally used VHF band I and
band III. Television on VHF was in black and white with
405-line display.British colour television was broadcast on Ultra high frequency (channels 21–69), beginning in the late 1960s. TV from then on was broadcast on both VHF and UHF (VHF being a monochromatic downconversion from the 625-line colour signal), with the exception of
BBC Two (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.
Unusually, the UK has an amateur radio allocation at
4 metres, 70-70.5 MHz.
United States
The general services in the VHF band are:
- 30–46 MHz: Licensed 2-way land mobile communication. Note: The 42 MHz Segment is still currently used by the California Highway Patrol, New Jersey State Police, and other state Troopers.
- 30–88 MHz: Military VHF-frequency modulation, including SINCGARS
- 43–50 MHz: Cordless telephones, 49 MHz FM walkie-talkies and radio controlled toys, and mixed 2-way mobile communication
- 50–54 MHz: Amateur radio 6 meters band; 50 MHz is an amateur-only radio control frequency
- 54–72 MHz: television channels 2-4
- 72–76 MHz: Radio controlled models and other devices; model aircraft operate on 72 MHz while surface models operate on 75 MHz
- 76–82 MHz: TV channel 5
- 82–88 MHz: TV channel 6
- 88–108 MHz: FM radio broadcasting (88–92 non-commercial, 92–108 commercial)
- 108–118 MHz: Air navigation beacons VHF omnidirectional range
- 118–132 MHz: Airband for air traffic control, Amplitude modulation, 121.5 MHz is emergency frequency
- 132–144 MHz: Auxiliary civil services, satellite, space research, and other miscellaneous services
- 144–148 MHz: Amateur band 2 Meters
- 148–156 MHz: "VHF Business band," the unlicensed Multi-Use Radio Service (MURS), and other 2-way land mobile, FM
- 156–174 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the maritime emergency and contact frequency. The 160 and 161 areas are American Association of Railroads 99 channel railroad radios issued to the railroad (Sample, AAR 21 is 160.425 and that is issued to Tennessee Valley Railroad Museum and other railroads that want AAR 21)
- 162.40–162.55: Weatheradio, narrowband FM
- 174–216 MHz: TV channels 7 through 13, and professional wireless microphones (low power, certain exact frequencies only)
- 216–222 MHz: reserved for future use
- 222–225 MHz: Amateur "1.25 meters" band (really closer to 1.33M)
- above 225 MHz: Federal services, notably military aircraft radio (225–400 MHz) AM, including HAVE QUICK, dGPS RTCM-104
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 microbroadcasting and sending output from
Compact Disk 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.
87.5-87.9 MHz
87.5-87.9 MHz is a radio frequency which, in most of the world, is used for FM broadcasting. In
North America, however, this bandwidth is allocated to
Very High Frequency television channel 6 (82-88MHz). The audio for TV channel 6 is broadcast at 87.75 MHz.
87.9 MHz is normally off-limits except for displaced class D stations which have no other frequencies in the normal 88.1-107.9 MHz subband on which to move. So far, only 2 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.
See also
ca:VHFcs:Velmi krátké vlnyda:VHFde:Ultrakurzwellees:VHF
fr:Très haute fréquenceko:VHF
it:Very high frequencynl:Ultrakorte golfja:超短波no:Veldig høy frekvens
pl:UKFpt:VHFksh:Ulltrakootwäll
ru:Ультракороткие волныfi:ULA
sv:VHFta:அதி உயர் அதிர்வெண்zh:甚高頻
{| align="right" border="0" class="wikitable"|-!
very high frequency (VHF)] to 1 m|}
Very high frequency (VHF) is the
radio frequency range from 30 megahertz to 300 megahertz. It is also known as the
meter band or
meter wave as the wavelengths range from ten to one
meters. Frequencies immediately below VHF are denoted High frequency, and the next higher frequencies are known as Ultra high frequency (UHF).
Common uses for VHF are
FM radio broadcast at 88–108 MHz and television broadcast (together with
ultra high frequency). VHF is also commonly used for terrestrial navigation systems (VHF omnidirectional range in particular), marine communications, and aircraft communications.
VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than low frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less bothered by buildings and other less substantial objects than higher frequencies.
Two unusual propagation conditions can allow much farther range than normal. The first, tropospheric ducting, can occur in front of and parallel to an advancing cold weather front, especially if there is a marked difference in humidities between the cold and warm air masses. A duct can form approximately 150 miles (240 km.) in advance of the cold front, much like a ventilation duct in a building, and VHF radio frequencies can travel along inside the duct, bending or refracting, for hundreds of miles. For example, a 50 watt Amateur FM transmitter at 146 MHz can talk from
Chicago, to
Joplin, Missouri, directly, and to
Austin, Texas, through a repeater. In a July 2006 incident, a
NOAA Weather Radio transmitter in north central Wisconsin was blocking out local transmitters in west central Michigan, quite far out of its normal range. The second type, much more rare, is called Sporadic-E, referring to the E-layer of the ionosphere. A sunspot eruption can pelt the Earth's upper atmosphere with charged particles, which may allow the formation of an ionized "patch" dense enough to reflect back VHF frequencies the same way HF frequencies are usually reflected (
skywave). For example, KMID (54–60 MHz) from
Midland, Texas was seen in near
Chicago, pushing out Chicago's own
WBBM-TV. These patches may last for seconds, or extend into hours. FM stations from
Miami, Florida, Florida;
New Orleans, Louisiana; Houston, Texas and even
Mexico were heard for hours in central
Illinois during one such event. Mid summer 2006 central Iowa stations were heard in Columbus, NE and blocking out
Omaha radio and TV stations for several days.
It was also easier to construct efficient transmitters, receivers, and antennas for it in the earlier days of radio, as compared to UHF. In most countries, the VHF spectrum is used for broadcast audio and television, as well as commercial two-way radios (such as those operated by taxis and police), marine two-way audio communications, and aircraft radios.
The large technically and commercially valuable slice of the VHF spectrum taken up by television transmission has attracted the attention of many companies and governments recently, with the development of more efficient digital television broadcasting standards. In some countries much of this spectrum will likely become available (probably for sale) in the next decade or so (currently scheduled for 2008 in the
United States).
Line of Sight Formula
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
Line-of-sight propagation phenomenon.
An approximation to calculate the line-of-sight horizon distance is:
- distance in miles = \sqrt{1.5 \times A_f} where A_f is the height of the antenna in feet
- distance in kilometres = \sqrt{12.7 \times A_m} where A_m is the height of the antenna in metres
Australia
The VHF TV band in Australia was originally allocated channels 1 to 10 - with the 2, 7 and 9 frequencies assigned for the initial services in Sydney and Melbourne, and later the same frequencies were assigned in Brisbane, Adelaide and Perth. Other capital cities and regional areas used a combination of these and other frequencies as available.
By the early
1960s it was apparent that the 10-channel spectrum was not going to be sufficient 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 required adjustment to enable tuning to the new frequencies.
Several TV stations were allocated to VHF channels 3, 4 and 5A, which were within the FM radio bands although not yet used for that purpose. A couple of notable examples were NBN Television
Newcastle, New South Wales,
WIN-4 Wollongong, New South Wales and Australian Broadcasting Corporation Illawarra on channel 5A. 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. Beginning in the
1990s, the Australian Broadcasting Authority began a process to move these stations to Ultra high frequency 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 frequencies, 9A and 12, have since been made available and are being used primarily for digital services (eg.
Australian Broadcasting Corporation in capital cities) but also for some new analogue services in regional areas.
New Zealand
- 44–51, 54–68 MHz: Band I Television (channels 1–3)
- 87.5–108 MHz: Band II Radio
- 174–230 MHz: Band III Television (channels 4–11)
In New Zealand, the four main Free-to-Air TV stations still use the VHF Television bands (
Band I and Band III) to transmit their programmes to New Zealand households. Other stations, including a variety of pay and regional free-to-air stations, broadcast their programmes using the Ultra high frequency band, since the VHF band is very overloaded with four stations sharing a very small frequency band. In some areas, the band is so overcrowded, that the C4 (TV channel) is not available.
United Kingdom
British television originally used VHF
band I and
band III. Television on VHF was in black and white with
405-line display.British colour television was broadcast on
Ultra high frequency (channels 21–69), beginning in the late 1960s. TV from then on was broadcast on both VHF and UHF (VHF being a monochromatic downconversion from the 625-line colour signal), with the exception of
BBC Two (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.
Unusually, the UK has an amateur radio allocation at
4 metres, 70-70.5 MHz.
United States
The general services in the VHF band are:
- 30–46 MHz: Licensed 2-way land mobile communication. Note: The 42 MHz Segment is still currently used by the California Highway Patrol, New Jersey State Police, and other state Troopers.
- 30–88 MHz: Military VHF-frequency modulation, including SINCGARS
- 43–50 MHz: Cordless telephones, 49 MHz FM walkie-talkies and radio controlled toys, and mixed 2-way mobile communication
- 50–54 MHz: Amateur radio 6 meters band; 50 MHz is an amateur-only radio control frequency
- 54–72 MHz: television channels 2-4
- 72–76 MHz: Radio controlled models and other devices; model aircraft operate on 72 MHz while surface models operate on 75 MHz
- 76–82 MHz: TV channel 5
- 82–88 MHz: TV channel 6
- 88–108 MHz: FM radio broadcasting (88–92 non-commercial, 92–108 commercial)
- 108–118 MHz: Air navigation beacons VHF omnidirectional range
- 118–132 MHz: Airband for air traffic control, Amplitude modulation, 121.5 MHz is emergency frequency
- 132–144 MHz: Auxiliary civil services, satellite, space research, and other miscellaneous services
- 144–148 MHz: Amateur band 2 Meters
- 148–156 MHz: "VHF Business band," the unlicensed Multi-Use Radio Service (MURS), and other 2-way land mobile, FM
- 156–174 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the maritime emergency and contact frequency. The 160 and 161 areas are American Association of Railroads 99 channel railroad radios issued to the railroad (Sample, AAR 21 is 160.425 and that is issued to Tennessee Valley Railroad Museum and other railroads that want AAR 21)
- 162.40–162.55: Weatheradio, narrowband FM
- 174–216 MHz: TV channels 7 through 13, and professional wireless microphones (low power, certain exact frequencies only)
- 216–222 MHz: reserved for future use
- 222–225 MHz: Amateur "1.25 meters" band (really closer to 1.33M)
- above 225 MHz: Federal services, notably military aircraft radio (225–400 MHz) AM, including HAVE QUICK, dGPS RTCM-104
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 microbroadcasting and sending output from
Compact Disk 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.
87.5-87.9 MHz
87.5-87.9 MHz is a radio frequency which, in most of the world, is used for
FM broadcasting. In
North America, however, this bandwidth is allocated to Very High Frequency television channel 6 (82-88MHz). The audio for TV channel 6 is broadcast at 87.75 MHz.
87.9 MHz is normally off-limits except for displaced class D stations which have no other frequencies in the normal 88.1-107.9 MHz subband on which to move. So far, only 2 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.
See also
ca:VHFcs:Velmi krátké vlnyda:VHF
de:Ultrakurzwellees:VHF
fr:Très haute fréquenceko:VHFit:Very high frequency
nl:Ultrakorte golfja:超短波no:Veldig høy frekvenspl:UKFpt:VHFksh:Ulltrakootwällru:Ультракороткие волны
fi:ULAsv:VHFta:அதி உயர் அதிர்வெண்zh:甚高頻
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