Spectre Electromagnetique
γ = Gamma rays
HX = Hard X-rays [3 EHz to 30 EHz]
X-rays are a form of ionizing radiation and as such can be dangerous.
SX = Soft X-Rays
EUV = Extreme ultraviolet
Being very energetic, UV can break chemical bonds, make molecules unusually reactive or ionize them, in general changing their mutual behavior. Sunburn, for example, is caused by the disruptive effects of UV radiation on skin cells, which can even cause skin cancer, if the radiation damages the complex DNA molecules in the cells (UV radiation is a proven mutagen).
NUV = Near ultraviolet Visible light [480 THz to 700 THz]
red ~ 625 to 740 nm ~ 480 to 405 THz
orange ~ 590 to 625 nm ~ 510 to 480 THz
yellow ~ 565 to 590 nm ~ 530 to 510 THz
green ~ 520 to 565 nm ~ 580 to 530 THz
cyan ~ 500 to 520 nm ~ 600 to 580 THz
blue ~ 430 to 500 nm ~ 700 to 600 THz
violet ~ 380 to 430 nm ~ 790 to 700 THz
NIR = Near infrared [120 to 400 THz] (2,500 to 750 nm).
Optical telecommunication in the near infrared is technically often separated to different frequency bands because of availability of light sources, transmitting /absorbing materials (fibers) and detectors.
O-band 1260–1360 nm
E-band 1360–1460 nm
S-band 1460–1530 nm
C-band 1530–1565 nm
L-band 1565–1625 nm
U-band 1625–1675 nm
MIR = Moderate infrared [30 to 120 THz] (10 to 2.5 μm)
Mid-infrared, from 30 to 120 THz (10 to 2.5 μm). Hot objects (black-body radiators) can radiate strongly in this range. It is absorbed by molecular vibrations, that is, when the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region since the mid-infrared absorption spectrum of a compound is very specific for that compound.
FIR = Far infrared [300 GHz to 30 THz]
Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in the Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere effectively opaque. However, there are certain wavelength ranges ("windows") within the opaque range which allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as "sub-millimeter" in astronomy, reserving far infrared for wavelengths below 200 μm.
Microwave frequency bands
Designation
Frequency range
L band 1 to 2 GHz
S band 2 to 4 GHz
C band 4 to 8 GHz
X band 8 to 12 GHz
Ku band 12 to 18 GHz
K band 18 to 26 GHz
Ka band 26 to 40 GHz
Q band 30 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
E band 60 to 90 GHz
W band 75 to 110 GHz
F band 90 to 140 GHz
D band 110 to 170 GHz
The above table reflects Radio Society of Great Britain (RSGB) usage. The term P band is sometimes used for UHF frequencies below L-band. For other definitions see Letter Designations of Microwave Bands
EHF = Extremely high frequency (Microwaves) [30 GHz to 300 GHz]
Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light. This band has a wavelength of one to ten millimetres, giving it the name millimeter band.
Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.
This band is commonly used in radio astronomy.
SHF = Super high frequency (Microwaves) [3 GHz to 30 GHz]
5 GHz Les protocoles de transmission sans fil pour réseaux locaux tels que Wi-Fi, bluetooth, DECT emploient également des micro-ondes dans la bande de 2,4 gigahertz, bien que quelques variantes emploient une bande de 5 gigahertz pour la communication
UHF = Ultrahigh frequency (Microwaves) [ 300 MHz to 3GHz ]
UHF and VHF are the most common frequency bands for television. Modern mobile phones also transmit and receive within the UHF spectrum, and UHF is widely used for two-way radio communication (usually using narrowband frequency modulation, but digital services are on the rise) by both public service agencies and the general public. Though television broadcasting is common on UHF, there has traditionally been very little radio broadcasting in this band until fairly recently; see digital audio broadcasting for details.
Characteristics
The transmission of radio waves from one point to another is affected by many variables such as atmospheric moisture, the stream of particles from the sun called solar wind, and time of day.
All radio waves are somewhat absorbed by atmospheric moisture. This reduces, or attenuates, the strength of radio signals over long distances. However, this effect increases according to the frequency: UHF signals are generally more degraded by moisture than lower bands such as VHF.
As well, the layer of the Earth's atmosphere called the ionosphere is filled with charged particles that can reflect radio waves. This can be helpful in transmitting a radio signal, since the wave bounces from the sky to the ground over and over, convering long distances. However, UHF benefits less from this effect than lower (VHF, etc.) frequencies.
As the atmosphere warms and cools throughout the day, UHF transmissions may be enhanced by tropospheric ducting.
Advantages
The main advantage of UHF transmission is that its high frequency means it has a physically short wave. Since the size of transmission and reception equipment (particularly antennas) is related to the size of the wave, smaller, less conspicuous antennas can be used than with VHF or lower bands.
Frequency Allocation - United States
A brief summary of some UHF frequency usage:
300–420 MHz: government use, including meteorology
420–450 MHz: radiolocation and Amateur "70 cm" band
450–470 MHz: UHF business band, GMRS, and FRS 2-way "walkie-talkies"
470–512 MHz: TV channels 14–20, public safety
512–698 MHz: TV channels 21–51
698–806 MHz: TV channels 52–69 (to be auctioned for other uses once conversion to digital TV has been accomplished)
806–824 MHz: pocket pagers and Nextel SMR band
824–849 MHz: Cellular phones, A & B franchises, mobile phone (USA GSM network)
849–869 MHz: public safety 2-way (fire, police, ambulance)
869–894 MHz: cellular phones, A & B franchises, base station
900 MHz GSM network (rest of the world)
902–928 MHz: ISM band: cordless phones and stereo, RFID, datalinks, Amateur radio 33cm band
928–960 MHz: mixed Studio-Transmitter Links, mobile 2-way, other
1240–1300 MHz: Amateur radio
1850–1910 MHz: PCS mobile phone—note below and GSM (1800 MHz)
1930–1990 MHz: PCS base stations—note below
note: order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz
2310–2360 MHz: Satellite radio (Sirius and XM)
2390–2450 MHz: Amateur radio, shared with below:
2400–2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN
2400 MHz 802.11b and 802.11g standards use the unlicensed 2.4 gigahertz (GHz)
around 2450 MHz: Microwave oven
VHF = Very high frequency [30 MHz to 300 MHz]
Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m).
United States
The general services in the VHF band are:
30–46 MHz: Licensed 2-way land mobile communication
30–88 MHz: Military VHF-FM, including SINCGARS
43–50 MHz: Cordless telephones, "49 MHz" FM walkie-talkies, and mixed 2-way mobile communication
50–54 MHz: Amateur radio "6-meter" band
54–72 MHz: TV channels 2, 3, and 4
72–76 MHz: Remote Control devices
76–88 MHz: TV channels 5 and 6
88–108 MHz: FM radio broadcasting (88–92 non-commercial, 92–108 commercial)
108–118 MHz: Air navigation beacons VOR
118–132 MHz: Airband for Air Traffic Control, AM, 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
148–174 MHz: "VHF Business Band," the new 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
162.40–162.55: NOAA Weather Stations, FM
174–216 MHz: TV channels 7 through 13, and professional wireless microphones (low power, certain exact frequencies only)
216–222 MHz: mixed services
222–225 MHz: Amateur "1-1/4-meter" band
above 225 MHz: Federal services, notably military aircraft radio (225–400 MHz) AM, including HAVE QUICK
HF = High frequency [3 MHz to 30 Mhz]
High frequency (HF) radio frequencies are between 3 and 30 MHz. This range is often called shortwave.
Since the ionosphere often reflects HF radio waves quite well, this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:
Sunlight/darkness at site of transmission and reception
Transmitter/receiver proximity to terminator
MF = Medium frequency [300 kHz to 3 MHz]
Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. They have the property of following the curvature of the earth, making them ideal for continuous, continental communications. Unlike shortwave radio, longwave signals do not reflect or refract using the ionosphere, so there are fewer phase-caused fadeouts. Instead, the D-layer of the ionosphere and the surface of the earth serve as a waveguide directing the signal.
LF = Low frequency [30 kHz to 300 kHz]
Low Frequency or LF (sometimes called longwave) refers to Radio Frequencies (RF) in the range of 30–300 kHz. In Europe, part of the LF spectrum is used for AM broadcast service. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. Time signal stations MSF, DCF77, JJY and WWVB are found in this band.
1.- AM radio is broadcast in on several frequency bands:
Long wave is 153–279 kHz
Medium wave is 530–1,710 kHz.
Short wave is 2,300–26,100 kHz, divided into 15 broadcast bands
Medium wave and short wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, refracting around the curve of the earth over a distance up to a few hundred kilometres (or miles) from the signal transmitter. However, after sunset, changes in the ionosphere cause AM signals to travel by skywave, enabling AM radio stations to be heard much farther from their point of origin than is normal during the day.
2.- LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from two or more stations to determine the position of a ship or aircraft. Before the popularity of the satellite-based GPS system, it was primarily used in marine applications. The current version of LORAN in common use is LORAN-C, which operates in the low frequency 90 to 110 kHz band.
VLF = Very low frequency [3 kHz to 30 kHz]
Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radionavigation. Because VLF waves can penetrate water only to a depth of roughly 10 to 40 metres (30 to 130 feet), depending on the frequency and the salinity of the water, they are used to communicate with submarines near the surface. (ELF is used for fully submerged vessels.)
VF = Voice frequency or ULF Ultra low Frequency [300 Hz to 3400 Hz]
A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech.
In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sample rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN
SLF Super Low Frequency [30 Hz to 300Hz]
Super Low Frequency (SLF) is the frequency range between 30 hertz and 300 hertz. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz).
ELF = Extremely low frequency [3 to 300 Hz]
ELF was used by the US Navy to communicate with submerged submarines. Because of the electrical conductivity of salt water, submarines are shielded from most electromagnetic communications
Reference
posted by Karim @ 8:06 PM
0 Comments:
Post a Comment
<< Home