# Directional or beam antennas which are intended to preferentially radiate or receive in a particular direction or directional pattern.

Directional antennas like Yagi-Uda antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired.

* Directional array refers to multiple antennas arranged such that the superposition of the electromagnetic waves produce a predictable electromagnetic field.

Directional antennas must be pointed at the transmitter they are receiving ; in most cases great accuracy is not needed.

* Directional Non-Force Technique-utilizes a diagnostic system for subluxation analysis consisting of gentle challenging and a unique leg check allowing the body to indicate the directions of misalignment of structures that are producing nerve interference.

* Another reason for using the Cassegrain design is to increase the focal length of the antenna, to improve the field of view Parabolic reflectors used in dish antennas have a large curvature and short focal length, to locate the focal point near the mouth of the dish, to reduce the length of the supports required to hold the feed structure or secondary reflector.

As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly ( or use directional antennas ) after sunset, or even to suspend broadcasting entirely during nighttime hours.

More recently, rooms designed to reduce reflection and external noise in radio frequencies have been used to test antennas, radars, or electromagnetic interference.

* use of directional antennas to reduce unwanted signals.

Satellite TV also began a digital transition, well before over the air broadcasting did the same, to increase satellite capacity and / or reduce the size of the receiving antennas, and this also made it more difficult for individuals to intercept these signals.

But all antennas have losses, such as power dissipated as heat in the resistance of its elements, nonuniform illumination by its feed, and radio waves scattered by structural supports and diffraction at the aperture edge, which reduce the power output.

Lotus effect superhydrophobic coatings applied to microwave antennas can significantly reduce rain fade and the buildup of ice and snow.

Practical inductors work as antennas, radiating a part of energy processed into surrounding space and circuits, and accepting electromagnetic emissions from other circuits, taking part in electromagnetic interference.

The relative amplitudes of — and constructive and destructive interference effects among — the signals radiated by the individual antennas determine the effective radiation pattern of the array.

* software defined antennas adaptively " lock onto " a directional signal, so that receivers can better reject interference from other directions, allowing it to detect fainter transmissions.

When a transcontinental or worldwide path is open on a particular frequency, digital, SSB and Morse code communication is possible using surprisingly low transmission powers, often of the order of tens of watts, provided suitable antennas are in use at both ends and that there is little or no man-made or natural interference.

It is sometimes used to prevent interference in terrestrial microwave links, where several antennas using the same frequency are located close together.

Radiation from the feed that falls outside the edge of the dish is called " spillover " and is wasted, reducing the gain and increasing the backlobes, possibly causing interference or ( in receiving antennas ) increasing susceptibility to ground noise.

If the position of the antennas is not known to sufficient accuracy or atmospheric effects are significant, fine adjustments to the delays must be made until interference fringes are detected.

Biconical ( or " bicon ") antennas are often used in electromagnetic interference ( EMI ) testing either for immunity testing, or emissions testing.

The land was set aside by the Federal Communications Commission in 1958, as a radio quiet zone ; the area closest to the telescope is free of fixed radio transmitters, and all other fixed radio transmitters including TV and radio towers inside the zone are required to transmit such that interference at the antennas is minimized by methods including limited power and using highly directional antennas.

Other gravitational wave antennas, such as LIGO, VIRGO, and GEO 600, are already in operation on Earth, but their sensitivity at low frequencies is limited by the largest practical arm lengths, by seismic noise, and by interference from nearby moving masses.

Features include even shorter antennas, up to 30 auto selecting channels, and higher resistance to interference.

The radio signals from the separate antennas overlapped in space, and the interference patterns between the individual signals was controlled to reinforce the signal in certain directions, and mute it in all others.

This is due, in large part, to the larger size of 6-meter antennas, power limitations in some countries outside the United States, and the 6-meter band's greater susceptibility to local electrical interference.

Since the picocell's antennas within the aircraft would be very close to the passengers and inside the aircraft's metal shell both the picocell's and the phones ' output power could be reduced to very low levels reducing the chance for interference.

In transmitting antennas, excessive side lobe radiation wastes energy and may cause interference to other equipment.

During much of the Cold War Soviet ( and Eastern Bloc ) jamming of some Western broadcasters led to a " power race " in which broadcasters and jammers alike repeatedly increased their transmission power, utilised highly directional antennas and added extra frequencies to the already heavily overcrowded shortwave bands to such an extent that many broadcasters not directly targeted by the jammers ( including pro-Soviet stations ) suffered from the rising levels of noise and interference.

By replicating this grouping across the country ( using different groups for adjacent transmitters ), co-channel interference can be minimised, and in addition, those in marginal reception areas can use more efficient grouped receiving antennas.

Examples of devices that use functional earth connections include surge suppressors and electromagnetic interference filters, certain antennas and measurement instruments.

Many early experiments found that any modification of the apparatus that can determine which slit a particle passes through will reduce the visibility of interference at the screen, thereby illustrating the complementarity principle: that light ( and electrons, etc.

The hypnotist's object is to use techniques to reduce interference and increase the receptability of specific messages ( suggestions ).

* Magnetic phonograph cartridges, which have a mu-metal case to reduce interference when LPs are played back

To reduce the visibility of interference between the chrominance signal and FM sound carrier required a slight reduction of the frame rate from 30 frames per second to 30 / 1. 001 ( approximately 29. 97 ) frames per second, and changing the line frequency from 15, 750 Hz to 15, 750 / 1. 001 Hz ( approximately 15, 734. 26 Hz ).

Zero-crossing detection may also be useful in triggering TRIACs at the best time to reduce mains interference and current spikes.

A post-exposure bake ( PEB ) is performed before developing, typically to help reduce standing wave phenomena caused by the destructive and constructive interference patterns of the incident light.

Signal processing is employed in radar systems to reduce the radar interference effects.

On June 12, 1992, 154 nations signed the UNFCCC, that upon ratification committed signatories ' governments to a voluntary " non-binding aim " to reduce atmospheric concentrations of greenhouse gases with the goal of " preventing dangerous anthropogenic interference with Earth's climate system ".

A balanced line allows a differential receiver to reduce the noise on a connection by rejecting common-mode interference.

The damaging effects of electromagnetic interference pose unacceptable risks in many areas of technology, and it is necessary to control such interference and reduce the risks to acceptable levels.

: In order to access the components, a housing is typically made in sections ( such as a box and lid ); an RF gasket is often used at the section joints to reduce the amount of interference that leaks through the joint.

However, in digital and radio frequency PCBs, the major reason for using large ground planes is to reduce electrical noise and interference being coupled from one part of the circuit to another through the ground ( ground loops ), and crosstalk between adjacent circuit traces.

Better-quality patch cables used in audio and electronic music have shielding to reduce interference and noise.

Spread-spectrum clock generation ( SSCG ) is used in some synchronous digital systems, especially those containing microprocessors, to reduce the spectral density of the electromagnetic interference ( EMI ) that these systems generate.

Note that this method does not reduce total radiated energy, and therefore systems are not necessarily less likely to cause interference.

The usefulness of this method as a means to reduce real-life interference problems is often debated, since it is perceived that spread-spectrum clocking hides rather than resolves higher radiated energy issues by simple exploitation of loopholes in EMC legislation or certification procedures.

While these do not add to the available number of conversations which can take place at once in a given area, they do reduce annoying interference experienced by users.

The end-fire subwoofer method, also called " forward steered arrays ", places subwoofer drivers co-axially in one or more rows, using destructive interference to reduce emissions to the sides and rear.

Sixteen enclosures in four rows were used in 2007 at one of the stages of the Ultra Music Festival, to reduce low frequency interference to neighboring stages.

Whilst providing no extra protection against wideband thermal noise, the frequency-hopping approach does reduce the degradation caused by narrowband interference sources.

People with cochlear implants, hearing aids, or neither of these devices can also use additional communication devices to reduce the interference of background sounds, or to mediate the problems of distance from sound and poor sound quality caused by reverberation and poor acoustic materials of walls, floors and hard furniture.

A special technique is used to reduce inter-symbol interference between the unshielded pairs.

To reduce interference from electrical equipment or metal in the fuselage of the aircraft, the MAD sensor is placed at the end of a boom or a towed aerodynamic device.

They will enable the main channel on each frequency to be broadcast with digital quality and to reduce the multipath interference that sometimes affects FM analog broadcasting.