TP-Link’s Omni-Directional, High-Gain Antennas extend coverage, improve performance, and provide stronger wireless coverage for several devices. Jul 19, 2014 Omni-directional antenna’s are vertical polarized. A Yagi antenna with vertical elements is also vertical polarized. But if you turn the antenna so that the elements are sideways, the antenna is then polarized horizontally. What is Antenna Gain? The range and strength at which an antenna can connect depends on the antenna’s gain.
This is article we have shared the details review of best omnidirectional tv antennas.
This post alone has help millions of people to choose best outdoor tv antenna for their home.
So lets dive in,
Gone are the times once the best omnidirectional TV antennas accustomed are available ugly styles.
With advanced technology and higher practices, these days outside Antennas are available all totally different distinctive styles and sizes.
If you get to urge to eliminate the monthly bills of cable or satellite subscription, then putting in a 100 mile omnidirectional TV Antenna for enjoying high-definition television programming could also be a possibility for you.
Several broadcast networks like CBS, ABC, Fox, NBC, etc. give TV signals freed from price.
What is the best outdoor omnidirectional antenna for free TV?
The sole price required, is for the acquisition of the HDTV-compatible Antenna.
Top 3 Best outdoor antennas
These over-the-air signals are powerful and supply an uncompressed image to your TV not like the cable supplier that executes knowledge compression resulting in image distortion at some level.
Outside high-definition best long range omnidirectional outdoor Tv Antenna is appropriate selection if you’re settled at a good distance from the printed towers or simply wish to strengthen the signal.
Totally different signal zones are color-coded which you simply ought to ascertain the right outside Antenna that matches into your region.
Best Long Range Omnidirectional Outdoor Antenna
When you are uninterested in paying the cable TV fee otherwise you suppose television system subscriptions are cost accounting you an excessive amount of annually, you’ll switch to an outside antenna.
These antennas will receive HD video and Dolby Digital 5.1 Sound and along with that, they’ll conjointly receive native channels from major networks like PBS, HBO, ABC, and so on.
Buying an outside antenna could be a wise selection.
However, it’s demanding to decide on the simplest antenna because the market is saturated with too several choices.
You won’t be able to attempt all of them and you may waste lots of your time if you opt to analysis all the antennas you’ll realize.
However, if you are looking for the best ones, we are here with you as we have brought the best list of outdoor HDTV antennas.
You will upgrade your TV to a full new level with an automate TV Box.
ViewTV Amplified Outdoor Omnidirectional HDTV Antenna
The ViewTV Amplified is our top omnidirectional tv Antenna is constructed to be put in outdoors providing free digital broadcast HD TV signals to your television.
You may simply want a indoor TV with a digital device box for receiving these signals.
It supports Full telecasting signal formats like 720p, 1080i and 1080p.
Integral High Gain electronic equipment operates silently and offers concerning a hundred and fifty miles of coverage.
The merchandise comes all-included with an impression box having twin TV Outputs.
The coax given this antenna is abundantly long having twelve meters of length.
The Wireless device provided permits 360-degree rotation of the antenna with the assistance of integral motor.
This motor rotates in each direction to avoid any type of entangling.
VIewTV out of doors Antenna works its finest inside the VHF 40~300 megahertz to radio frequency 470~890 MHz frequency ranges.
it’s weatherproof in addition, to befittingly work underneath any atmospheric condition circumstances.
The aggregation of this antenna is extremely straightforward and can simply take couple of minutes.
It is simply mounted to a pole having concerning 1” of diameter.
it’s extremely suggested to mount this antenna thirty feet on top of ground.
Best Affordable Omnidirectional Outdoor Antennas
Amplified Outdoor HDTV Antenna by Tree New Bee
Tree New Bee introduces this Amplified out of doors telecasting Antenna that includes integral Low-Noise electronic equipment and UHF/VHF/FM
Radio reception with a hundred and fifty miles of coverage for choosing up TV channels, free from any type of satellite or cable payment.
This telecasting directional antenna has an integral rotor, a Rotor management box and a wireless remote controller for 360-degree rotation of this rotor.
The provided forty feet of RG6 coax is abundantly long for a stable association.
The antenna is connected to any pole with a diameter of one” or 1.125” on the roof or attic.
But, the vary of this Amplified out of doors telecasting Antenna could modification as per your location settings.
The environment with immense buildings or mountains, etc.
would possibly poorly have an effect on the aptitude of receiving signals for this antenna.
It works best inside the VHF 40~300 MHz and radio frequency 470~890 MHz frequency ranges.
This is one of the best outdoor tv antenna has been integrated with Pure Vertex Technology that has the aptitude to signal from different appliances.
BoostWaves out of doors electronic equipment telecasting Antenna encompasses a solid ABS material construction with a water-proof style for a stable association even within the atmospheric condition conditions.
The Antenna comes with an integral rotor, Rotor management Box, twin TV Outputs and Infrared Remote Controller for full 360-degree rotation of the rotor.
It provides high sensitivity HDTV/UHF/ VHF and FM Radio Reception with a variety of a hundred twenty-five miles.
BoostWaves Outdoor Amplified HDTV Antenna works its finest inside the frequency ranges of VHF 40~300MHz and radio frequency 470~860MHz.
The Antenna is given an Installation Kit for users’ quality that has 50ft. of RG6 coax, twenty cable clips and twenty Cable Safety Ties.
It’s terribly straightforward to put in and needs no assembly.
Integral Gain Boost and therefore the Low-Noise electronic equipment offer full 1080p telecasting signals with its Supreme Amplification.
it’s a collapsible style for fast and straightforward movability.
It’s been backed with one year of guarantee amount and might be mounted within the attic, roofs, or aspect of the house.
Best VHF, UHF and HDTV Outdoor Antenna
Vilso Outdoor Digital HDTV Antenna
Vilso out of doors Antenna provides free digital broadcast high-definition television signals with a coverage vary of regarding one hundred fifty miles.
Made of high-quality material, it provides high reception among operative frequency vary of VHF 40~300 MHz and UHF 470~890 MHz.
It supports most of the high-definition television signal formats like 720p, 1080i and 1080p.
Enclosed with Wireless remote controller, the motor may be controlled by this remote controller to rotate the antenna in 360 degrees.
The motor rotates in each the directions to avoid web.
Integrated with low-noise and high Gain electronic equipment, the Vilso Digital HDTV Antenna can develop most of your local news, climate, baby, sports channels, etc.
Totally free of cost and you just need to connect the antenna to your television.
A long cable with 12-meter length is provided for easy installation of the antenna over the house for great reception.
The antenna is constructed to be weather-resistant for better durability.
The product has been backed with 30-day money-back guarantee for best after-sales support.
It can be mounted on a pole with 1” of diameter and takes just few minutes to assemble.
Designed with a flex mount system, Winegard FlatWave Air Attic HDTV Antenna has a compact, sleek and stylish construction, perfect for enhancing outdoor looks.
The FlatWave Air Attic is best omnidirectional tv antenna has been totally integrated with one of the best and super low-noise split band digital Amplifier and along with that, the antenna generates high-quality and clear images than the other huge Outdoor Antennas.
It provides great reception without any sort of idlers or pixilation.
Winegard FlatWave can be mounted anywhere as per your convenience like attic, decks or rooftops orat the side of your home and takes few minutes for its easy installation.
With reflector incorporated in the antenna, it receives both UHF and VHF signals from a coverage range of about 60+ miles.
This HDTV antenna has been designed with one of the best and Clear Circuit Technology and along with that, the FlatWave Air Attic Antenna offers absolutely high-quality HDTV signals.
The programming allows free over-the-air local channels of news, sports, kids, weather, movies and other first-rate TV shows as well.
It is a fixed-type of antenna and has been backed with a spectacular one year of Manufacturer’s guarantee amount.
Best 100 mile omnidirectional tv antenna
1byone 100 Miles Digital Amplified Outdoor / Roof TV Antenna Extremely High Performance for UHF Band
This 1byone can receive signals inside an 80-mile radius from a broadcast tower.
This superior TV antenna makes TV free forever as you won’t want cable TV or satellite subscription to observe your favorite TV shows, news, and sports channels.
It’ll catch all native HD channels broadcasted inside an 80-mile radius from wherever you put in the antenna.
You will like it as a result of it’s terribly simple to put in.
It comes with an installation guide that produces your life easier.
Once put in, it will intercept 1080p, immoderate HD 4K, and 3D channels that are being broadcasted in your space.
If your native broadcast is in Dolby Digital 5.1 Surround Sound, you may be able to receive it on your TV via this antenna.
The 1byone HD antenna will receive TV and UHF signals. this suggests you may have a large vary of channels to observe while not having to pay a monthly fee for cable or satellite.
However, the signal strength, terrain, and distance of broadcast tower can verify the standard of sound and movie you get.
If you’re living off from a broadcast tower, take care to show it towards the tower once mounting it on your roof.
To take care that you just can receive HD channels, take care to be told concerning the programs out there in your space.
You’ll hunt for native broadcasters on the net.
If you’re victimisation this antenna for an TV flat screen, take care to check if your TV contains an inherent tuner.
You will ought to install a third-party HD receiver just in case it doesn’t provide you with the choice to tune channels.
This antenna contains a superior construction.
It will face up to robust out of doors conditions with none issues.
It has a cross-phase and multi-element kind that means that you just get nice vary and quality.
Features:
- Receives UHF signals
- 80-mile radius
- Easy to put in
- You can watch HD TV at a crisp quality
- Excellent construction allows it to face up to robust out of doors conditions
- Cross-phase and multi-element construction
Best 4K Outdoor Omnidirectional Antennas
8 Element Bowtie Indoor/Outdoor TV Antenna – 70 Mile Range
A 70-mile vary is pretty nice in terms of vary power.
However, this vary depends on the placement and obstructions.
Moreover, the signal has got to taste concrete and different arduous artefact, therefore the vary are affected.
However overall this is often one amongst those antennas that bring an excellent investment within the end of the day.
With the eight component Indoor and out of doors Antenna, you’ll simply watch several high networks like NBC, CBS, ABC, PBC, and lots of a lot of.
It simply receives Full HD content because of the standard technology utilised in its producing It is one amongst the best antennas to mount if you rigorously scan the directions.
It has a really versatile product therefore you’ll install it inside or outdoors, reckoning on your desires.
It comes with an unrestricted mounting hardware that produces it simple to put in it outdoors.
If you’re curst any step, merely open the manual and browse directions.
The manual has easy-to-follow directions.
It utilised proprietary technology to produce a transmission boost of 17.4 dBi.
The antenna contains a distinctive style that enables it to focus on broadcasting towers all told directions.
Bowtie makes a specialty of leading edge technology. The corporate has been creating these merchandise for quite sixty years currently.
This is strongest omnidirectional tv antenna deploys breakthrough technology that delivers exceptional reception even with a tiny low style.
The high-quality reflector strengthens the signals in order that you’ll relish HD quality audio/video anytime.
To set it up, purpose it to the direction of broadcasting towers first of all. Connect the cable returning from the antenna to your TV simply the manner you connect an everyday transmission line.
Once your TV is connected to the antenna, use the inherent channel search to seek out any programs you would like.
If you’re having hassle with the reception, modification its location and direction till you discover the most effective place for optimum signal strength.
Without paying any monthly cable fee, you may be able to watch free programs on demand.
If a neighborhood broadcaster with a broadcast tower in an exceedingly 70-mile radius is giving Dolby Sound and immoderate HD video, you may be able to catch the signal victimisation the component Bowtie.
You’ll simply watch CBS, ABC, PBS, and lots of different channels from high networks with this antenna while not sacrificing audio/video quality.
Features:
- 70-mile vary
- Supports TV
- Indoor / out of doors antenna
- Exceptional reception
- Cutting-edge technology
- Easy to put in
Xtreme Signal Long Range Yagi aerial vogue VHF/UHF HDTV Antenna
The Xtreme Signal Long vary Yagi aerial vogue is one in all the simplest HD antennas returning at an inexpensive worth.
It will receive signals returning from the 70-mile radius broadcast tower with ease.
This suggests you’ll be able to receive most the native HD channels while not having to pay a dime.
![Long Long](/uploads/1/2/5/0/125035833/341701680.jpg)
To understand that channels you’ll be able to watch in your space, check your native broadcasters.
You’ll be able to simply search broadcasters in your space via the web. This antenna receives radio frequency and VHF signals.
This suggests you may have an enormous type of HD channels to get pleasure from while not paying even one greenback on big-ticket subscriptions.
It comes with the mandatory mounting hardware, that makes it very straightforward to put in.
The mounting tools work with the quality one.6’’ masts. If you can’t discern the way to mount the antenna, scan the manual that comes with it.
The Xtreme Signal Long Range Yagi aerial vogue VHF/UHF HDTV Antenna contains a 75-ohm constitutional electrical device.
This digital electrical device is weatherproof thus you’ll be able to simply install the outside with none worries as a result of it’ll face up to harsh weather.
once shopping for it, you’ll be able to expect higher signal strength compared to different HD antennas.
This can be as a result of the rear reflector that actively reduces interference.
This is one in all the simplest out of doors antennas in terms of vary, worth for the cash and simple use.
this can be most likely one in all my favorites and that undoubtedly is suggested for your home.
Features
- VHF and radio frequency receiver
- 70-mile vary
- Watch native HD channels while not having to pay monthly subscriptions
- Built-in digital waterproof electrical device
- Back reflector for low interference
Channel Master CM-4228HD High VHF, radio frequency and HDTV Antenna
The Channel Master Antenna receives the favoured VHF and radio frequency signals.
If your native tower is broadcasting HDTV signal, this antenna can receive it.
it’ll additionally receive FM signals as a result of i’s bandwidths starting from 174 to 216 and 470 and 700 megacycles per second.
This is over again, one in all the simplest antennas in terms of vary since it will receive signal returning from eighty miles away.
You’ll be able to watch HD channels and luxuriate in Ray M.
Dolby crisp sound?
make sure to examine whether or not your native broadcasters have a broadcasting tower inside associate 80-mile radius of your home before creating the investment.
![Gain Gain](/uploads/1/2/5/0/125035833/306230494.jpg)
Mounting it mustn’t be an enormous problem.
You’ll be able to scan directions on the manual to mount it properly.
It comes pre-assembled with a constitutional balloon.
It includes the mandatory hardware for installation however you may have to be compelled to obtain a mast severally because it doesn’t accompany the merchandise.
Once put in, the antenna offers a 75-ohm output.
This antenna by Channel Master could be a phased with eight bays.
It’s multi-directional, which implies you don’t have to be compelled to purpose it to the broadcasting tower to receive a stronger signal.
It’ll receive signals from a hundred and eighty degrees vary with none problems.
this can be one in all the qualities that are exhausting to search out in different product.
With this antenna, you’ll be able to watch HD channels broadcasted by your native station.
However, that’s not it. it’ll additionally acquire major TV networks like PBS, HBO, FOX, and CBS.
Meaning you won’t miss your favorite show ever once more, even after you have unsubscribed from satellite and cable.
Features:
- UHF, VHF and HDTV reception
- 80 mile radius
- Watch native channels and major networks like PBS, ABC, and FOX
- Versatile mounting choices
Amplified HD Digital Outdoor HDTV Antenna 150 Miles Long Range with Motorized 360 Degree Rotation
The Amplified HD Digital Outdoor HDTV Antenna 150 Miles Long Range with Motorized 360 Degree Rotation has a tremendous 150-mile range.
It comes with a motorized controller which will offer a 360-degree rotation and associated to you and furthermore might get an infrared remote with it.
The wireless remote makes it straightforward to manage the HDTV antenna.
You’ll be able to move the rotor victimization this controller and change the direction for best image and audio quality.
This antenna will intercept VHF, UHF, and FM radio frequencies inside a 150-mile radius.
The constitutional 360-degree rotor provides simple use.
You don’t need to visit the antenna to regulate its direction, simply use the remote that comes with the device to maneuver the rotor.
This HDTV antenna comes with a constitutional low noise electronic equipment.
This new technology ensures minimum noise even once the signal is returning from a protracted distance.
If the signal is weak as a result of interference or obstructions, the low noise electronic equipment can amplify the signal to present you the right image and sound on your TV.
This Amplified Antenna is intended to spice up signal.
It has a parabolic focusing reception and a constitutional high gain booster. you may ne’er see poor footage or audio as a result of poor signal once more.
The device contains a constitutional FM receiver that permits you to pay attention to native radio stations on your TV.
It comes with the HDTV antenna itself, a constitutional rotor, a constitutional electronic equipment, a rotor management box, a distant management, coax cable, and power offer.
That’s everything you would like to start out enjoying cable free access and eliminate the supererogatory prices.
You don’t need to visit an ironmongery store to shop for something, not even the antenna wire.
simply open the box and install the antenna for a high-quality audio/video expertise.
Features:
- 360-degree rotation
- Dual TV output to attach to a pair of displays at identical time
- Wireless remote controller
- One of the best vary antennas
- VHF/UHF/FM radio
- Low-noise electronic equipment
How to opt for Best Outdoor Omnidirectional Antenna for HDTV
If you would like to save lots of yourself from the valuable cable subscription and want a cheaper means, then over-the-air Antenna are going to be a perfect alternative for you that provide crystal clear HD native channels at no cost.
Below given are some things to think about whereas shopping for an outside Antenna:
Channels out there in your region: To put in a TV Antenna, you must apprehend what varieties of channels are out there in your space.
Sure websites like AntennaWeb, TV Fool or Antennas Direct would possibly assist you with this procedure.
It’ll take address input from the users and can offer helpful results like list of channels out there in this space, signal strength, radio frequency channels out there, VHF channels out there, directions they’re returning from, etc.
Suitable Antenna for these Channels and your location: If there are totally different broadcasts signals returning from different directions then you may need to think about shopping for an Omni-directional antenna.
They’re usually simple to put in, you may get many channels from totally different broadcast towers and that they don’t would like frequent adjusting.
On the opposite hand, if you discover that the published channels gettable to your originating from single direction, then the antennas are going to be an optimum purchase.
They provide robust signal strength and frequently have a lot of coverage vary than the Omni-directional ones.
VHF/UHF: sure antennas are specifically engineered to select up radio frequency channels, some for VHF, whereas others are capable of choosing each.
However, it’s not necessary that the UHF/VHF Antenna are going to be superior in reading each of them, one would possibly overpower the standard of alternative.
After installation: when putting in place the Antenna, modification the line input to ‘Antenna’.
Then execute Automatic channel scan.
All the channels are going to be listed then you’ll check the strength or quality of those channels.
If the signal strength isn’t that satisfactory, you’ll try and improve the standard by:
Changing the direction or location of the antenna
Integrate a symptom electronic equipment for higher reception (if it’s not already included)
Purchase an extended line for higher affiliation
[Final Words]
So, this was our guide to buy omnidirectional tv antenna fo 2019 and if you too are planning to buy one for yourself, then all
you have to do is to just go ahead and check the factors before buying one and if you find one in your budget, then make sure that you research about it accordingly and check online reviews and pricing in order to make it the best buy for you.
Here, we have given some of the best reviews regarding these outdoor HDTV antennas and if you like them or want to buy it for somebody you care about, make sure you share it with them.
Best 10 Natural Gas Detector Review For Home SafetyAlso, if you have any questions or queries regarding any of the products here, then you can easily ask them out in the comment section below and we will be sure to answer those queries for you.
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John Hattich
Article
5
Contents
Introduction
This document gives basic antenna definitions and discusses antenna concepts with a focus on the pros and cons of omni and directional antennas.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
This document is not restricted to specific software and hardware versions.
Conventions
Refer to Cisco Technical Tips Conventions for more information on document conventions.
Basic Definitions and Antenna Concepts
An antenna gives the wireless system three fundamental properties: gain, direction and polarization. Gain is a measure of increase in power. Gain is the amount of increase in energy that an antenna adds to a radio frequency (RF) signal. Direction is the shape of the transmission pattern. As the gain of a directional antenna increases, the angle of radiation usually decreases. This provides a greater coverage distance, but with a reduced coverage angle. The coverage area or radiation pattern is measured in degrees. These angles are measured in degrees and are called beamwidths.
An antenna is a passive device which does not offer any added power to the signal. Instead, an antenna simply redirects the energy it receives from the transmitter. The redirection of this energy has the effect of providing more energy in one direction, and less energy in all other directions.
Beamwidths are defined in both horizontal and vertical plains. Beamwidth is the angular separation between the half power points (3dB points) in the radiation pattern of the antenna in any plane. Therefore, for an antenna you have horizontal beamwidth and vertical beamwidth.
Figure 1: Beamwidth of AntennaAntennas are rated in comparison to isotropic or dipole antennas. An isotropic antenna is a theoretical antenna with a uniform three-dimensional radiation pattern (similar to a light bulb with no reflector). In other words, a theoretical isotropic antenna has a perfect 360 degree vertical and horizontal beamwidth or a spherical radiation pattern. It is an ideal antenna which radiates in all directions and has a gain of 1 (0 dB), i.e. zero gain and zero loss. It is used to compare the power level of a given antenna to the theoretical isotropic antenna.
Figure 2: Radiation Pattern of an Isotropic AntennaAntennas can be broadly classified as omnidirectional and directional antennas, which depends on the directionality.
Unlike isotropic antennas, dipole antennas are real antennas. The dipole radiation pattern is 360 degrees in the horizontal plane and approximately 75 degrees in the vertical plane (this assumes the dipole antenna is standing vertically) and resembles a donut in shape. Because the beam is slightly concentrated, dipole antennas have a gain over isotropic antennas of 2.14 dB in the horizontal plane. Dipole antennas are said to have a gain of 2.14 dBi, which is in comparison to an isotropic antenna. The higher the gain of the antennas, the smaller the vertical beamwidth is.
Imagine the radiation pattern of an isotropic antenna as a balloon, which extends from the antenna equally in all directions. Now imagine that you press in on the top and bottom of the balloon. This causes the balloon to expand in an outward direction, which covers more area in the horizontal pattern, but reduces the coverage area above and below the antenna. This yields a higher gain, as the antenna appears to extend to a larger coverage area.
Figure 3: Radiation Pattern of an Omni AntennaOmnidirectional antennas have a similar radiation pattern. These antennas provide a 360 degree horizontal radiation pattern. These are used when coverage is required in all directions (horizontally) from the antenna with varying degrees of vertical coverage. Polarization is the physical orientation of the element on the antenna that actually emits the RF energy. An omnidirectional antenna, for example, is usually a vertical polarized antenna.
Figure 4: Antenna PolarizationDirectional antennas focus the RF energy in a particular direction. As the gain of a directional antenna increases, the coverage distance increases, but the effective coverage angle decreases. For directional antennas, the lobes are pushed in a certain direction and little energy is there on the back side of the antenna.
Figure 5: Radiation Pattern of a Directional AntennaAnother important aspect of the antenna is the front-to-back ratio. It measures the directivity of the antenna. It is a ratio of energy which antenna is directing in a particular direction, which depends on its radiation pattern to the energy which is left behind the antenna or wasted. The higher the gain of the antenna, the higher the front-to-back ratio is. A good antenna front-to-back ratio is normally 20 dB.
Figure 6: Typical Radiation Pattern of a Directional Antenna with Calibrated LobesAn antenna can have a gain of 21 dBi, a front-to-back ratio of 20 dB or a front-to-side ratio of 15 dB. This means the gain in the backward direction is 1 dBi, and gain off the side is 6 dBi. In order to optimize the overall performance of a wireless LAN, it is important to understand how to maximize radio coverage with the appropriate antenna selection and placement.
Indoor Effects
Wireless propagation can be effected by reflection, refraction or diffraction in a particular environment. Diffraction is the bending of waves around the corners. RF waves can take multipaths between the transmitter and receiver. A multipath is a combination of a primary signal and reflected, refracted or diffracted signal. So on the receiver side, the reflected signals combined with the direct signal can corrupt the signal or increase the amplitude of the signal, which depends on the phases of these signals. Because the distance traveled by the direct signal is shorter than the bounced signal, the time differential causes two signals to be received.
These signals are overlapped and combined into a single one. In real life, the time between the first received signal and the last echoed signal is called the delay spread. Delay spread is the parameter used to signify multipath. The delay of the reflected signals is measured in nano seconds. The amount of delay spread depends upon the amount of obstacles or infrastructure present between the transmitter and receiver. Therefore, delay spread has more value for the manufacturing floor due to lot of metallic structure present as compared to the home environment. Overall, multipath limits the data rate or lowers the performance.
Figure 7: Multipath Effects in Indoor EnvironmentIndoor RF propagation is not the same as it is outdoors. This is due to the presence of solid obstructions, ceilings, and floors that contribute to attenuation and multipath signal losses. Therefore, multipath or delay spread is more in the indoor environment. If the delay spread is more, the interference is more and will cause lower throughput at a particular data rate.
Indoor environment can also be classified as near line of sight (LOS) and non LOS. In near LOS environments, where you can see access points (APs) such as in the hallways, multipath is usually minor and can be overcome easily. The amplitudes of the echoed signals are much smaller than the primary one. However, in non LOS conditions, the echoed signals can have higher power levels, because the primary signal might be partially or totally obstructed, and generally more multipath is present.
Multipath has been a semi-fixed event. However, other factors such as moving objects can enter into play. The particular multipath condition changes from one sample period to the next. This is called time variation.
Multipath interference can cause the RF energy of an antenna to be very high, but the data is unrecoverable. You should not limit the analysis only to the power level. As low RF signal does not mean poor communication, but low signal quality does mean poor communication. You must analyze signal quality and Rx level side by side. High Rx level and low signal quality means there is a lot of interference. You must analyze the channel frequency plan again in such a scenario. Low Rx level and low signal quality means that there is a lot of blockage.
Indoor wave propagation is also affected by the building material. The density of the materials used in the construction of a building determines the number of walls the RF signal can pass through and still maintain adequate coverage. Paper and vinyl walls have little effect on signal penetration. Solid walls, solid floors and pre-cast concrete walls can limit signal penetration to one or two walls without degrading coverage. This can vary widely based any steel reinforcing within the concrete. Concrete and concrete block walls can limit signal penetration to three or four walls. Wood or drywall typically allows for adequate penetration of five or six walls. A thick metal wall causes signals to reflect off, which results in poor penetration. Steel reinforced concrete flooring restricts coverage between floors to perhaps one or two floors.
The higher the frequency, the shorter the wavelength is. Shorter wavelengths have more probability to get absorbed and distorted by a building material. Therefore, 802.11a, which operates in a higher frequency band, is more prone to the building material effect.
The actual effect on the RF must be tested at the site. Therefore, a site survey is necessary. You should do a site survey to see the signal level you receive on the other side of the walls. A change in the type of antenna and location of the antenna can eliminate multipath interference.
Omni Antenna Pros and Cons
Omni antennas are very easy to install. Due to the 360 degrees horizontal pattern, it can even be mounted upside down from a ceiling in the indoor environment. Also, because of its shape it is very convenient to attach these antennas to the product. For example, you might see Rubber Duck antennas attached to the wireless APs. In order to obtain an omnidirectional gain from an isotropic antenna, energy lobes are pushed in from the top and the bottom, and forced out in a doughnut type pattern. If you continue to push in on the ends of the balloon (isotropic antenna pattern), a pancake effect with very narrow vertical beamwidth results, but with a large horizontal coverage. This type of antenna design can deliver very long communications distances, but has one drawback which is poor coverage below the antenna.
Figure 8: Omni Antenna with No Coverage Below the AntennaIf you try to cover an area from a high point, you see a big hole below the antenna with no coverage.
This problem can be partially solved with the design of something called downtilt. With downtilt, the beamwidths are manipulated to provide more coverage below the antenna than above the antenna. This solution of downtilt is not possible in an omni antenna because of the nature of its radiation pattern.
The omni antenna is usually a vertically polarized antenna, so you cannot have advantages of using cross polarization here to fight interference.
A low gain omni antenna provides a perfect coverage for an indoor environment. It covers more area near the AP or a wireless device in order to increase the probability of receiving the signal in a multipath environment.
Note: In addition to the Cisco Aironet Antennas that work for larger deployments, HGA9N and HGA7S are High-Gain Omnidirectional antennas supported by Cisco for Small Office Environments.
Directional Antenna Pros and Cons
With the directional antennas, you can divert the RF energy in a particular direction to farther distances. Therefore, you can cover long ranges, but the effective beamwidth decreases. This type of antenna is helpful in near LOS coverage, such as covering hallways, long corridors, isle structures with spaces in between, etc. However, as the angular coverage is less, you cannot cover large areas. This is a disadvantage for general indoor coverage because you would like to cover a wider angular area around the AP.
Antenna arrays should face in the direction where the coverage is desired, which can sometimes make mounting a challenge.
Interference
As 802.11 devices operate in the unlicensed bands, this makes it available for anyone to use. WLAN interference comes from other similar devices and other sources such as microwave ovens, cordless phones, radar signals from a nearby airport, etc. Interference is also found from other technologies that use the same band as Bluetooth or security devices. In the 2.4 GHz unlicensed there are limited channels to utilize to avoid interference, with only three non-overlapping channels available.
Interference and multipath cause the receive signal to fluctuate at a particular frequency. This variation of signal is called fading. Fading is also frequency selective, as attenuation varies with frequency. A channel can be classified as either a fast fading channel or slow fading channel. This depends on how rapidly the transmitted base band signal changes. A mobile receiver that travels through an indoor environment can receive rapid signal fluctuations caused by additions and cancellations of the direct signals at half wavelength intervals.
Interference increases the requirement of signal to noise ratio (SNR) for a particular data rate. The packet retry count goes up in an area where interference or multipath is very high. A change in the type of antenna and location of the antenna can eliminate multipath interference. Antenna gain adds to the system gain and improves signal and interference to noise ration (SINR) requirements as shown here:
Figure 9: Noise Floor and Signal and Interference to Noise RatioAlthough directional antennas help to focus the energy in a particular direction which can help to overcome fading and multipath, multipath itself reduces the focusing power of a directional antenna. The amount of multipath seen by a user at a long distance from the AP can be much more.
Directional antennas used for the indoors typically have a lower gain, and as a result, have a lower front-to-back and front-to-side lobe ratios. This results in less ability to reject or reduce the interference signals received from directions outside the primary lobe area.
Conclusion
While directional antennas can be of great value for certain indoor applications, the vast majority of indoor installations utilize omnidirectional antennas for the reasons cited in this document. The selections of an antenna, directional or omnidirectional, should be strictly determined by a correct and proper site survey.