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• Low Frequency
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Power line communication - Long haul, low frequency
Utility companies use special coupling
capacitors to connect radio transmitters to
the power-frequency AC conductors
1
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Power line communication - Long haul, low frequency
1
On some powerlines in the former
Soviet Union, PLC-signals are not fed
into the high voltage line, but in the
ground conductors, which are
mounted on insulators at the pylons.
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Power line communication - Long haul, low frequency
While utility companies use
microwave and now, increasingly,
fiber optic cables for their primary
system communication needs, the
power-line carrier apparatus may still
be useful as a backup channel or for
very simple low-cost installations that
do not warrant installing fiber optic
lines.
1
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Power line communication - Long haul, low frequency
1
Power line carrier communication (PLCC) is
mainly used for telecommunication, teleprotection and tele-monitoring between
electrical substations through power lines at
high voltages, such as 110 kV, 220 kV, 400
kV. The major benefit is the union of two
applications in a single system, which is
particularly useful for monitoring electric
equipment and advanced energy
management techniques (such as OpenADR
and OpenHAN).
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Power line communication - Long haul, low frequency
The modulation generally used in
these system is amplitude
modulation. The carrier frequency
range is used for audio signals,
protection and a pilot frequency. The
pilot frequency is a signal in the audio
range that is transmitted continuously
for failure detection.
1
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Power line communication - Long haul, low frequency
1
The voice signal is compressed and filtered
into the 300 Hz to 4000 Hz range, and this
audio frequency is mixed with the carrier
frequency. The carrier frequency is again
filtered, amplified and transmitted. The
transmission power of these HF carrier
frequencies will be in the range of 0 to +32
dbW. This range is set according to the
distance between substations. PLCC can be
used for interconnecting private branch
exchanges (PBXs).
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Power line communication - Long haul, low frequency
To sectionalize the transmission
network and protect against failures, a
"wave trap" is connected in series with
the power (transmission) line
1
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Power line communication - Long haul, low frequency
1
A coupling capacitor is used to connect the
transmitters and receivers to the high
voltage line. This provides low impedance
path for carrier energy to HV line but
blocks the power frequency circuit by
being a high impedance path. The
coupling capacitor may be part of a
capacitor voltage transformer used for
voltage measurement.
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Power line communication - Long haul, low frequency
Power line carriers may change its
transmission system from analog to
digital to enable Internet Protocol
devices. Digital power line carrier
(DPLC) was developed for digital
transmission via power lines. DPLC has
the required quality of bit error rate
characteristics and transmission ability
such as transmitting information from
monitored electric-supply stations and
images.
1
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Power line communication - Long haul, low frequency
1
Power line carrier systems have long
been a favorite at many utilities
because it allows them to reliably
move data over an infrastructure that
they control. Many technologies have
multiple applications. For example, a
communication system bought
initially for automatic meter reading
can sometimes also be used for load
control or for demand response
applications.
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Power line communication - Long haul, low frequency
1
A PLC carrier repeating station is a facility,
at which a power line communication
(PLC) signal on a powerline is refreshed.
Therefore the signal is filtered out from the
powerline, demodulated and modulated on
a new carrier frequency, and then
reinjected onto the powerline again. As
PLC signals can carry long distances
(several 100 kilometres), such facilities
only exist on very long power lines using
PLC equipment.
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Power line communication - Long haul, low frequency
PLC is one of the
technologies used for
automatic meter reading
1
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Power line communication - Long haul, low frequency
In a one-way (inbound only) system,
readings "bubble up" from end devices
(such as meters), through the
communication infrastructure, to a "master
station" which publishes the readings. A
one-way system might be lower-cost than
a two-way system, but also is difficult to
reconfigure should the operating
environment change.
1
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Power line communication - Long haul, low frequency
In a two-way system (supporting both
outbound and inbound), commands can
be broadcast out from the master station
to end devices (meters) -- allowing for
reconfiguration of the network, or to obtain
readings, or to convey messages, etc
1
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Powerline Digital Subscriber Line - Long haul, low frequency
Utility companies use special
coupling capacitors to connect radio
transmitters to the power-frequency
AC conductors
1
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Powerline Digital Subscriber Line - Long haul, low frequency
power-line carrier communication
(PLCC) is mainly used for
telecommunication, tele-protection
and tele-monitoring between
electrical substations through power
lines at high voltages, such as 110 kV,
220 kV, 400 kV. The major benefit is
the union of two applications in a
single system, which is particularly
useful for monitoring electric
1
https://store.theartofservice.com/the-low-frequency-toolkit.html
Powerline Digital Subscriber Line - Long haul, low frequency
The voice signal is compressed and
filtered into the 300Hz to 4000Hz range,
and this audio frequency is mixed with the
carrier frequency. The carrier frequency is
again filtered, amplified and transmitted.
The transmission power of these HF
carrier frequencies will be in the range of 0
to +32 Decibel|dbW. This range is set
according to the distance between
substations.
1
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Powerline Digital Subscriber Line - Long haul, low frequency
To sectionalize the transmission
network and protect against failures, a
wave trap is connected in series with
the power (transmission) line
1
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Powerline Digital Subscriber Line - Long haul, low frequency
power-line carriers may change its
transmission system from analog to
digital to enable Internet Protocol
devices. Digital power-line carrier
(DPLC) was developed for digital
transmission via power lines. DPLC has
the required quality of bit error rate
characteristics and transmission ability
such as transmitting information from
monitored electric-supply stations and
1
https://store.theartofservice.com/the-low-frequency-toolkit.html
Powerline Digital Subscriber Line - Long haul, low frequency
1
power-line carrier systems have long
been a favorite at many utilities
because it allows them to reliably
move data over an infrastructure that
they control. Many technologies have
multiple applications. For example, a
communication system bought
initially for automatic meter reading
can sometimes also be used for load
control or for demand response
https://store.theartofservice.com/the-low-frequency-toolkit.html
Powerline Digital Subscriber Line - Long haul, low frequency
1
A PLC carrier repeating station is a
facility, at which a power-line
communication (PLC) signal on a
Electric power
transmission|powerline is refreshed.
Therefore
https://store.theartofservice.com/the-low-frequency-toolkit.html
Powerline Digital Subscriber Line - Long haul, low frequency
the signal is filtered out from the
powerline,
Demodulation|demodulated and
Modulation|modulated on a new
Carrier wave|carrier frequency, and
then reinjected onto the powerline
again. As PLC signals can carry long
distances (several 100 kilometres),
such facilities only exist on very long
power lines using PLC equipment.
1
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Powerline Digital Subscriber Line - Long haul, low frequency
In a one-way (inbound only) system,
readings bubble up from end devices
(such as meters), through the
communication infrastructure, to a master
station which publishes the readings. A
one-way system might be lower-cost than
a two-way system, but also is difficult to
reconfigure should the operating
environment change.
1
https://store.theartofservice.com/the-low-frequency-toolkit.html
Powerline Digital Subscriber Line - Long haul, low frequency
1
In a two-way system (supporting both
outbound and inbound), commands
can be broadcast out from the master
station to end devices (meters) –
allowing for reconfiguration of the
network, or to obtain readings, or to
convey messages, etc
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Super low frequency
Another conflicting designation which
includes this frequency range is Extremely
Low Frequency (ELF), which in some
contexts refers to all frequencies up to 300
hertz.
1
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Super low frequency
1
It became operational in 1989 but was
discontinued in 2004 due to advances in
Very low frequency|VLF communication
systems
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Super low frequency
1
The requirements for receivers at SLF
frequencies is less stringent than
transmitters, because the signal
strength (set by atmospheric noise) is
far above the noise floor of the
receiver, so small, inefficient antenna
(radio)|antennas can be used
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Surround sound - Low Frequency Effects (LFE) channel
Because the low-frequency effects
channel requires only a fraction of the
bandwidth of the other audio
channels, it is referred to as the .1
channel; for example 5.1 or 7.1.
1
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Surround sound - Low Frequency Effects (LFE) channel
The LFE is a source
of some confusion in
surround sound
1
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Surround sound - Low Frequency Effects (LFE) channel
In the original movie theater
implementation, the LFE was a separate
channel fed to one or more subwoofers
1
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Surround sound - Low Frequency Effects (LFE) channel
1
Some record labels such as Telarc and
Chesky have argued that LFE channels
are not needed in a modern digital
multichannel entertainment system
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Radio frequencies - Extremely Low frequency RF
1
High-power extremely Low frequency
RF with electric field levels in the low
kV/m range are known to induce
perceivable currents within the
human body that create an annoying
tingling sensation
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Radio frequencies - Extremely Low frequency RF
page 63[http://www.who.int/pehemf/publications/elf_ehc/en/index.html
Extremely Low Frequency Fields
Environmental Health Criteria Monograph
No.238], chapter 5, page 121, WHO
1
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Low frequency
1
'Low frequency' or 'low freq' or 'LF'
refers to Radio frequency|radio
frequencies (RF) in the range of
30kHzndash;300kHz
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Low frequency - Propagation
Because of their long wavelength, low
frequency radio waves can
Diffraction|diffract over obstacles like
mountain ranges and follow the curvature
of the Earth. This mode of propagation,
called ground wave, is the main mode in
the LF band. The attenuation of signal
strength with distance by absorption in the
ground is lower than at higher frequencies.
Low frequency ground waves can be
1
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Low frequency - Propagation
1
Low frequency waves can also travel long
distances by reflecting from the
ionosphere (the actual mechanism is one
of refraction), although this method, called
skywave or skip propagation, is not as
common as at higher frequencies.
Reflection occurs at the Kennelly–
Heaviside layer|E layer or F Region|F
layers. Skywave signals can be detected
at distances exceeding 300km from the
transmitting antenna.
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Low frequency - Standard time signals
1
In the frequency range 40kHz–80kHz, there are
several standard time and frequency stations,
such as
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Low frequency - Standard time signals
1
* HBG Prangins|HBG in Prangins, Switzerland
(75kHz) (closed down on 1 January 2012)
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Low frequency - Standard time signals
In Europe and Japan, many low-cost
consumer devices have since the late 1980s
contained radio clocks with an LF receiver for
these signals. Since these frequencies
propagate by ground wave only, the precision
of time signals is not affected by varying
propagation paths between the transmitter,
the ionosphere, and the receiver. In the
United States, such devices became feasible
for the mass market only after the output
power of WWVB was increased in 1997 and
1999.
1
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Low frequency - Military
1
Radio signals below 50kHz are capable
of penetrating ocean depths to
approximately 200 metres, the longer
the wavelength, the deeper. The British,
German, Indian, Russian, Swedish,
United States and possibly other
navy|navies communicate with
submarines on these frequencies.
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Low frequency - Military
In addition, Royal Navy nuclear
submarines carrying ballistic missiles are
allegedly under standing orders to monitor
the BBC Radio 4 transmission on 198kHz
in waters near the UK. It is rumoured that
they are to construe a sudden halt in
transmission, particularly of the morning
news programme Today
Programme|Today, as an indicator that the
UK is under attack, whereafter their sealed
1
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Low frequency - Military
1
In the US, the Ground Wave Emergency
Network or GWEN operated between 150
and 175kHz, until replaced by satellite
communications systems in 1999. GWEN
was a land based military radio
communications system which could
survive and continue to operate even in
the case of a nuclear attack.
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Low frequency - Experimental and amateur
An international 2.1kHz allocation, the
2200-meterband (135.7kHz to 137.8kHz),
is available to amateur radio operators in
several countries in Europe,European
Conference of Postal and
Telecommunications
Administrations|CEPT/ERC
Recommendation 62-01 E (Mainz 1997):
Use of the band 135.7-137.8 kHz by the
Amateur Service
1
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Low frequency - Experimental and amateur
1
The UK allocated a 2.8kHz sliver of
spectrum from 71.6kHz to 74.4kHz
beginning in April 1996 to UK
amateurs who applied for a Notice of
Variation to use the band on a
noninterference basis with a
maximum output power of 1 W ERP
(effective radiated power)
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Low frequency - Experimental and amateur
1
In the United States, there is a special
license free allocation in the longwave
range called LowFER
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Low frequency - Meteorological information broadcasts
A regular service transmitting
radioteletype|RTTY marine meteorological
information in SYNOP code on LF is the
German Meteorological Service
(Deutscher Wetterdienst or
[http://www.dwd.de DWD]). The DWD
operates station DDH47 on 147.3kHz
using standard ITA-2 alphabet with a
transmission speed of 50 baud and FSK
modulation with 85Hz shift.
1
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Low frequency - Radio navigation signals
1
In parts of the world where there is no
longwave broadcasting service, Nondirectional beacons or NDB's used for
aeronavigation operate on 190–300kHz
(and beyond into the MW band). In
Europe, Asia and Africa, the NDB
allocation starts on 283.5kHz.
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Low frequency - Radio navigation signals
The commercial DATATRAK radio
navigation system operates on a number
of frequencies, varying by country,
between 120 and 148kHz.
1
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Low frequency - Radio broadcasting
1
The longwave radio broadcasting service
operates on frequencies between 148.5
and 283.5kHz in Europe and parts of Asia.
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Low frequency - Other applications
1
Some radio frequency identification (RFID)
tags utilize LF. These tags are commonly
known as LFID's or LowFID's (Low
Frequency Identification). The LF RFID
tags are near field devices.
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Low frequency - Antennas
1
Since the ground waves used in this band
require vertical polarization, vertical
antennas are used for transmission,
usually mast radiators, either insulated
from the ground and fed at the bottom, or
occasionally fed through guy-wires
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Low frequency - Antennas
1
The height of antennas differ by
usage.
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Low frequency - Antennas
For some non-directional beacons
(NDBs) the height can be as low as 10
meters, while for more powerful
navigation transmitters such as Decca
Navigator System|DECCA, masts with a
height around 100 meters are used. Tantennas have a height between 50 and
200 meters, while mast aerials are
usually taller than 150 meters.
1
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Low frequency - Antennas
The height of mast antennas for
LORAN-C is around 190 meters for
transmitters with radiated power below
500kW, and around 400 meters for
transmitters greater than 1000
kilowatts. The main type of LORAN-C
antenna is insulated from ground.
1
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Low frequency - Antennas
LF Longwave|(longwave) broadcasting
stations use mast antennas with heights of
more than 150 meters or T-aerials. The
mast antennas can be ground-fed
insulated masts or upper-fed grounded
masts. It is also possible to use cage
antennas on grounded masts.
1
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Low frequency - Antennas
For broadcasting stations,
directional antennas are often
required
1
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Low frequency - Antennas
1
For reception, long wire antennas are
used, or more often ferrite loop
antennas because of their small size.
Amateur radio operators have achieved
good LF reception using active
antennas with a short whip.
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Low frequency - Antennas
LF transmitting antennas for high
power transmitters require large
amounts of space, and have been the
cause of controversy in Europe and the
United States due to concerns about
possible electromagnetic radiation
and health|health hazards associated
with exposure to high-power radio
waves.
1
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Extremely low frequency
1
'Extremely low frequency' ('ELF') waves
are electromagnetic radiation (radio
waves) with frequencies from
3to30Hertz|Hz, and corresponding
wavelengths from 100,000 to 10,000
kilometers. In atmosphere science, an
alternative definition is usually given, from
3Hzto3kHz.Liemohn, Michael W. and A. A.
CHAN, [http://lwstrt.gsfc.nasa.gov/trt_liemohn05eos.pdf
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Extremely low frequency
1
In the related magnetosphere science,
the lower frequency electromagnetic
oscillations (pulsations occurring
below ~3Hz) are considered to lie in
the ultra low frequency|ULF range,
which is thus also defined differently
from the ITU Radio Bands.
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Extremely low frequency
ELF radio waves are generated by
lightning and natural disturbances in
Earth's magnetic field, so they are a
subject of research by atmospheric
scientists
1
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Radiation - Very low frequency (VLF)
Very low frequency, or VLF, refers to a
frequency range of 30 Hz to 3kHz which
corresponds to wavelengths of 100,000 to
10,000 meters respectively. Since there is not
much bandwidth in this range of the radio
spectrum, only the very simplest signals can
be transmitted, such as for radio navigation.
Also known as the myriameter band or
myriameter wave as the wavelengths range
from ten to one myriameter (an obsolete
metric unit equal to 10 kilometers).
1
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Radiation - Extremely low frequency (ELF)
Extremely low frequency (ELF) is
radiation frequencies from 3 to 30Hz
(108 to 107 meters respectively). In
atmosphere science, an alternative
definition is usually given, from 3Hz
to 3kHz. In the related magnetosphere
science, the lower frequency
electromagnetic oscillations
(pulsations occurring below ~3Hz) are
considered to lie in the ULF range,
1
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Inductive coupling - Low frequency induction
Low frequency induction is an
unwanted form of inductive coupling,
which can occur when a metallic
Pipeline transport|pipeline is
installed parallel to a high-voltage
power line. The pipeline, which is a
conductor, and is insulated from the
earth by its protective coating, can
develop voltages which are hazardous
to personnel operating valves or
1
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Radio navigation - Low frequency radio range
1
The low-frequency radio range (LFR,
also other names) was the main
navigation system used by aircraft for
Instrument flight rules|instrument
flying in the 1930s and 1940s in the U.S.
and other countries, until the advent of
the VOR in the late 1940s. It was used
for both enroute navigation as well as
instrument approaches.
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Radio navigation - Low frequency radio range
1
The ground stations consisted of a set
of four antennas that projected Lorenz
beams in four cardinal directions
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Radiological - Very low frequency (VLF)
Very low frequency, or VLF, refers to a
frequency range of 30Hz to 3kHz which
corresponds to wavelengths of 100,000 to
10,000 meters respectively. Since there is
not much bandwidth in this range of the
radio spectrum, only the very simplest
signals can be transmitted, such as for
radio navigation. Also known as the
myriameter band or myriameter wave as
the wavelengths range from ten to one
myriameter (an obsolete metric unit
equal to 10 kilometers).
1
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Antenna height considerations - Longwave/low frequency antennas
1
At VLF, LF and Medium frequency|MF the
Radio masts and towers|radio mast or
tower is often used directly as an antenna
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Antenna height considerations - Longwave/low frequency antennas
For high power transmitters, masts
with heights of about half the radiated
wavelength are preferred because they
concentrate the radiated power toward
the horizon. This enlarges the distance
at which selective fading occurs.
However, masts with heights of around
half a wavelength are much more
expensive than shorter ones and often
too expensive for lower power
1
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Antenna height considerations - Longwave/low frequency antennas
1
For longwave transmitters, however,
the construction of halfwave masts is
infeasible in most cases, either for
economic reasons or because of
problems with flight safety
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Antenna height considerations - Longwave/low frequency antennas
Use is not normally made of masts
higher than five-eighths (5/8) of a
wavelength, because such masts
(except for some special constructions
for high power mediumwave
broadcasting) exhibit poor vertical
radiation patterns. The heights of
masts for mediumwave transmitters
normally do not exceed the 300 metre
(1000foot) level.
1
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Antenna height considerations - Longwave/low frequency antennas
Sometimes cage aerials or longwire
aerials are used for LF and MF
transmission. In this case the height of the
tower may be greater than is usually the
case. Because towers or masts used for
cage or long wire aerials are grounded at
the base, they are especially suitable for
supporting antennas for Ultra high
frequency|UHF or VHF broadcasting.
1
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Ultra low frequency
Gordeev, [http://www.nat-hazardsearth-syst-sci.net/3/203/2003/nhess3-203-2003.pdf Preseismic ULF
electromagnetic effect from
observation at Kamchatka], Natural
Hazards and Earth System Sciences,
Volume 3, Pages 203-209, 2003
Frequencies above 3Hz in atmosphere
science are usually assigned to the
extremely low frequency|ELF range.
1
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Ultra low frequency
Many types of waves in the ULF
frequency band can be observed in
the magnetosphere and on the ground.
These waves represent important
physical processes in the near-Earth
plasma environment. The speed of the
ULF waves is often associated with the
Alfvén velocity that depends on the
ambient magnetic field and plasma
mass density.
1
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Ultra low frequency
1
This band is used for communications in
Mining|mines, as it can penetrate the
earth.[http://www.weather.nps.navy.mil/~ps
guest/EMEO_online/module3/module_3_1
.html HF and Lower Frequency Radiation Introduction]
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Ultra low frequency - Earthquakes
1
Some monitoring stations have reported
that earthquakes are sometimes preceded
by a spike in ULF activity
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Ultra low frequency - Earth mode communications
1
ULF has been used by the military for secure
communications through the ground
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Very low frequency
'Very low frequency' or 'VLF' is the
International Telecommunications
Union|ITU designation for radio
frequency|radio frequencies (RF) in the
range of 3 kHz to 30 kHz and
wavelengths from 10 to 100 kilometres
1
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Very low frequency - Propagation characteristics
1
Because of their large wavelengths, VLF
radio waves can Diffraction|diffract around
large obstacles and so are not blocked by
mountain ranges, and can propagate as a
ground wave following the curvature of the
Earth
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Very low frequency - Propagation characteristics
VLF waves have very low path
attenuation, 2-3 dB per 1000km, with little
of the fading experienced at higher
frequencies, This is because VLF waves
are reflected from the bottom of the
ionosphere, while higher frequency
shortwave signals are returned to Earth
from higher layers in the ionosphere, the
F1 layer|F1 and F2 layer|F2 layers, by a
refraction process, and spend most of their
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Very low frequency - Propagation characteristics
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VLF waves can penetrate seawater to a
depth of at least 10 to 40 meters (30 to
130 feet), depending on the frequency
employed and the salinity of the water, so
they are used to communicate with
submarines.
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Very low frequency - Antennas
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A major practical drawback to this band is
that because of the length of the waves,
full size resonant antennas (half wave
dipole or monopole antenna|quarter wave
monopole antennas) cannot be built
because of their physical height
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Very low frequency - Antennas
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Transmitting antennas for VLF frequencies are
very large wire antennas, up to a mile across
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Very low frequency - Antennas
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To minimize power dissipated in the
ground, these antennas require
extremely low resistance ground
systems. Because of soil resistance,
Counterpoise (ground
system)|counterpoise systems are
often used, consisting of radial
networks of copper cables supported
several feet above the ground under
the antenna, extending out radially
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Very low frequency - Antennas
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The requirements for receiving antennas
are less stringent, because the transmitter
power is generally high to overcome
atmospheric noise. Atmospheric noise
and not Noise figure|receiver noise
determines the receiver signal to noise
ratio, so small inefficient receiving
antennas can be used. Loop antennas
are often used for reception.
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Very low frequency - Applications
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The frequency range below 9kHz is not
allocated by the International
Telecommunication Union and may be
used in some nations license-free.
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Very low frequency - Applications
VLF is used to Communication with
submarines|communicate with
submarines near the surface (for
example using the transmitter VLF
transmitter DHO38|DHO38), while
Extremely low frequency|ELF is used
for deeply submerged vessels. VLF is
also used for radio navigation beacons
(alpha) and time signals (beta). VLF is
also used in Electromagnetic
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Very low frequency - Applications
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In the USA, the time signal station WWVL
began transmitting a 500W signal on
20kHz in August 1963. It used Frequency
Shift Keying (Frequency-shift keying|FSK)
to send data, shifting between 20kHz and
26kHz. The WWVL service was
discontinued in July 1972.
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Very low frequency - Applications
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Historically, this band was used for
transcontinental radio communication
during the wireless telegraphy era
between about 1900 and 1925
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Very low frequency - Applications
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Naturally occurring signals in the VLF band are used
for long range lightning location
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Very low frequency - Applications
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and for research into phenomena such as
Upper-atmospheric lightning|transient
luminous events. Measurements of
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Very low frequency - VLF submarine communication methods
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High power land-based transmitters in
countries that operate submarines
send signals that can be received
thousands of miles away
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Very low frequency - VLF submarine communication methods
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Because of the low bandwidth available
it is not possible to transmit audio
signals, therefore all messaging is
done with alphanumeric data at very
low bit rates. Three types of modulation
are used:
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Very low frequency - VLF submarine communication methods
* OOK / CWK: On-Off Keying /
Continuous Wave Keying. Simple
Morse code transmission mode where
carrier on = mark and off = space.
This is the simplest possible form of
radio transmission, but it is difficult
for transmitters to transmit high
power levels, and the signal can easily
be swamped by atmospheric noise, so
this is only really used for
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Very low frequency - VLF submarine communication methods
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* FSK: Frequency-shift keying. The oldest
and simplest form of digital radio data
modulation. Frequency is increased by
25Hz (for example) from the carrier to
indicate a binary “1” and reduced by 25Hz
to indicate binary “0”. FSK is used at rates
of 50 bit/s and 75 bit/s.
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Very low frequency - VLF submarine communication methods
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* MSK: Minimum-shift keying. A more
sophisticated modulation method that
uses less bandwidth for a given data
rate than FSK. This is the normal
mode for submarine communications
today, and can be used at data rates up
to 300 bit/s- or about 35 8-bit ASCII
characters per second (or the
equivalence of a sentence every two
seconds) – a total of 450 words per
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Very low frequency - VLF submarine communication methods
Two alternative character sets may be
used: 5-bit ITA2 or 8-bit ASCII. Because
these are military transmissions they are
almost always encrypted for security
reasons. Although it is relatively easy to
receive the transmissions and convert
them into a string of characters, civilians
cannot decode any encrypted messages
because they most likely use one-time
pads since the amount of text is so small.
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Very low frequency - PC-based VLF reception
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VLF signals are often monitored by radio
amateurs using simple homemade VLF
radio receivers based on personal
computers (PCs)
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Very low frequency - PC-based VLF reception
These spectrograms show many
signals, which may include VLF
transmitters and the horizontal electron
beam deflection of TV sets. The
strength of the signal received can vary
with a Sudden Ionospheric
Disturbance. These cause the
ionization level to drop in the
atmosphere. The result of this is that
the VLF signal will reflect down to Earth
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Super-low frequency
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Another conflicting designation which
includes this frequency range is
Extremely Low Frequency (ELF), which
in some contexts refers to all
frequencies up to 300 hertz.
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Super-low frequency
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It became operational in 1989 but was
discontinued in 2004 due to advances
in Very low frequency|VLF
communication systems
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Non-ionizing radiation - Very low frequency (VLF)
Very low frequency or VLF is the radio
frequencies (RF) in the range of 3 to
30kHz. Since there is not much bandwidth
in this band of the radio spectrum, only the
very simplest signals are used, such as for
radio navigation. Also known as the
myriameter band or myriameter wave as
the wavelengths range from ten to one
myriameter (an obsolete metric unit equal
to 10 kilometers)
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Non-ionizing radiation - Extremely low frequency (ELF)
Extremely low frequency (ELF) is the
range of radiation frequencies from 3 to
30Hz. In atmosphere science, an
alternative definition is usually given, from
3Hz to 3kHz. In the related
magnetosphere science, the lower
frequency electromagnetic oscillations
(pulsations occurring below ~3Hz) are
considered to be in the ULF range, which
is thus also defined differently from the
ITU Radio Bands.
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Genome instability - Low frequency of mutations without cancer
The protein coding regions of the
human genome, collectively called
the exome, constitutes only 1.5% of
the total genome. As pointed out
above, ordinarily there are only an
average of 0.35 mutations in the
exome per generation (parent to child)
in humans. In the entire genome
(including non-protein coding
regions) there are only about 70 new
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Planck (spacecraft) - Low Frequency Instrument
The LFI has three frequency bands,
covering the range of 30–70GHz, covering
the microwave to infra-red regions of the
electromagnetic spectrum. The detectors
use high-electron-mobility transistors.
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Common-emitter amplifier - Low frequency voltage amplifier
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A typical example of the use of a common-emitter
amplifier is shown in Figure 3.
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Common-emitter amplifier - Low frequency voltage amplifier
The input capacitor C removes any
constant component of the input, and the
resistors R1 and R2 bias the transistor so
that it will remain in active mode for the
entire range of the input
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