Wireless LOS Terminology

November 28, 2013 at 10:00 AM

Why Line of Sight (LOS) is so important

 

Sample of LOS and Fresnel Zone Diagram

When designing an outdoor wireless network, ask yourself this: what is between point A (antenna 1) and point B (antenna 2)? This path between two antennas is referred to as the Line of Sight (LOS).

 

There are three main categories of Line of Sight. Full Line of Sight (LOS) is where no obstacles reside between the two antennas. Near Line of Sight (nLOS) includes partial obstructions such as tree tops between the two antennas. Lastly, Non Line of Sight (NLOS) is where full obstructions exist between the two antennas.

 

By determining the specific Line of Sight conditions in the WiFi network area you can then determine the correct type of wireless system to install.

 

Another common term to be aware of is The Fresnel Zone, referenced in the diagram above. It is is an electromagnetic phenomenon where light waves or radio signals get diffracted or bent from solid objects near their path. The radio waves reflecting off the objects may arrive out of phase with the signals that traveled directly to the receiving antenna, thus reducing the power of the received signal.

 

Line of Site (LOS) Overview Diagram

Print and post the above diagram.

 

For indoor wireless network installations it is important to consider obstacles such as walls, ceilings, and furniture that will affect Line of Sight since these all play a role in wireless signal reception. In wireless transmissions, reflections (when wireless signals "bounce" off objects) and multipath (when wireless signals travel in multiple paths arriving at the receiver at different times) are as important as signal strength in determining the success of an installation. A signal will also exhibit peaks and nulls in its amplitude and alteration of its polarization (vertical or horizontal) when propagating through walls, ceilings and reflecting off metallic objects. 

 

Path Loss is another area of concern when dealing with Line of Sight. For instance, although 2.4 GHz signals pass rather well through walls, passing through trees and leaves is a challenge. This is due to the difference of water content in each. Radio waves in the 2.4 GHz band absorb into water very easily, so the high level of moisture in trees or leaves would trap the waves. When faced with nLOS or NLOS conditions due to trees, 900 MHz is your best choice as it is not absorbed like 2.4 GHz.

 

 

Click here to shop L-com’s Hyperlink brand wireless products.

  

Tips for Buying Coaxial Cable

August 14, 2013 at 10:00 AM

 

What’s right for your application?

 

Selecting the proper coaxial cable can go a long way toward satisfying the needs of a specific application. Which criteria are most important to the specifying process? There are 4 key points to be considered when choosing coaxial cables:

 

      RG174/U Bulk Coaxial Cable - Flexible Small Diameter 50 Ohm Cable

 

 

 

 

 

 

1. Cable Type

 

There are basically two types of coaxial cables: those with an impedance of 75 Ohms (Ω), used mostly for video applications, and those with an impedance of 50 Ω, used mostly for data and wireless communications.

 

Typical 75 Ω cables are our RG59/U and RG6/U. These cable types are available in 100-, 500- and 1000-foot reels.

 

Typical RG-style 50 Ω cables for data are RG174/U, RG188/U and RG316/U. These bulk cables can be used in applications where cable assemblies must be built in the field. Available in 100-, 500- and 1000-foot rolls, their stranded 26 AWG center conductors result in very flexible cables for tight-fit applications. Additionally, the bulk RG188A/U cable has a Teflon-taped outer jacket to help achieve a 200-degree C operating temperature, and the RG316/U has an extruded FEP outer jacket that helps achieve a 200-degree C operating temperature.

 

50 Ω cables are also available in the low-loss version: 100-, 200-, and 400-series specifically for wireless applications. Low Loss coaxial cables provide far better shielding than their RG style counterparts and are best suited for RF applications.

 

 

2. Operating Frequency

 

Another important consideration is the operating frequency of the signal carried on the cable. As the frequency increases, the signal energy moves away from the cable's center conductor to the cable's shield outside of the conductor, a phenomenon known as the "skin effect".

 

This has a direct correlation to how far the signal can travel over a cable of a certain length, for a given signal frequency and power level. The higher the signal frequency, the shorter the distance traveled.

 

For our full Coaxial Cabling Tutorial, click here.

 

 

3. Cable Attenuation

 

Cable attenuation is the amount of signal loss over a specific distance. In general, the higher the frequency, the larger the attenuation will be. The larger the diameter of a cable's center conductor, the lower the attenuation is.

 

For example, an RG59/U cable with a 14 AWG center conductor can carry a signal (at a specific frequency and power level) about twice the distance as that of an RG11/U cable with a 20 AWG center conductor. It's imperative to know how much cable attenuation is acceptable in your particular application when selecting coaxial cable.

 

 

4. Characteristic Impedance

 

A coaxial cables characteristic impedance is an important parameter that affects the performance of the signal being carried over the cable. Also known as transmission impedance, it is defined as the relationship between a cable's capacitance per unit length to its inductance per unit length. For optimum signal transfer, the cable's characteristic impedance should be matched to the impedance/resistance of the load.

 

RG59A/U Bulk Coaxial Cable - Stranded Center Conductor 75 Ohm Cable
50 Ohm BNC Crimp Plug for RG58 - Amphenol #31-320-RFX
See a Matrix of Data
and Wireless Coax Cable Assemblies for Easy Ordering
Looking for bulk 75Ω cable for audio/video? See it here!
Get Coax Connectors
from L-com and build your own cable assemblies!
 
Quick note: RG-style coaxial cables are not all built the same. Check the specification requirements before you buy, and if you need help contact our technical support.
 

DB9 D-Subminiature Connectors : Advantages and Disadvantages

June 19, 2013 at 10:00 AM

9-pin D-Sub connectors (DB9 or DE-9)

 

DB9 Connector on Cable

For many years, serial communication was one of the chief methods of connecting peripherals (such as joysticks, printers, and scanners) to PCs. The most common connector type for serial communication was the 9-pin D-Subminiature connector, or sometimes called a DB9 or a DE-9.

 

Nine pins were plenty to carry the data in series, and though there were many drawbacks to DB9 connectors which eventually lead to them becoming legacy in favor of standards like USB, there are still many devices with DB9 ports or cables on them today.

 

 

What are the disadvantages?

 

The connectors themselves are large, making them difficult to connect and disconnect in tight spaces. Also, the pins are exposed in the shell, so they can be easily bent or broken off. Though the connector can be mated without using the thumbscrew hardware, it does not tend to hold as well using just friction-fitting. If you do use the thumbscrews, the connector takes much longer to plug in and unplug.

 

Finally, serial communication tends to be slow, especially over longer lengths, and unexpected breaks in communication could cause software on the PC to freeze. All of these problems led to other standards becoming more popular for the same applications.

 

However, this does not mean that the DB9 connector is a lost cause. There are actually solutions available for many of the problems mentioned above. For instance, right angle adapters solve the tight-space problem by allowing a tight angle without damaging the connector. Widely available D-Subminiature plug and jack covers can protect pins from damage when not mated, and adapters like gender changers and socket savers can reduce the stress caused by repeated mating cycles.

 

 

On the other hand...

 

ES4-232 4-Port Ethernet to DB9 Adapter and Device Server

DB9 connectors have advantages too. In general they are far easier to customize, with at least 9 individual pins to carry serial data. Though the speed is slower than other standards, the length of the cable can be much longer. USB, for instance, has a five-meter length limit, but RS-232 (the most common standard for serial data) has no defined length limit, and RS-422 has been used at lengths hundreds of meters long with special equipment.

 

Also- Don't worry if you have an old device that only has DB9 connectors on it. Even with D-Subminiature being mostly legacy, there are plenty of options for conversion. Converters to and from USB, Ethernet, and other standards are common and can allow you to use your device on any computer today.

 

Examples of Applications for Serial Converters

If you're looking to find DB9 Connectors: L-com carries products ranging from economical serial cables with many off-the-shelf lengths to high-quality premium cables for demanding applications. Also check out L-com's D-Subminiature adapters for innovative solutions to common problems, and L-com's bulk cable, connectors, adapter kits and tools for do-it-yourself components.
 

How To Differentiate VGA, SVGA and UXGA

May 8, 2013 at 4:38 PM

 

VGA Cable

While knowing these specific terms is helpful in buying some analog display equipment (such as computer monitors), each refers to the same type of video format. These acronyms relate to the resolution a monitor supports, thus the same type of cabling and connectors are used.

 

Another common denominator with VGA, SVGA, and UXGA is that they are all mostly now legacy. No new products are being built using VGA analog video interfaces. 

 

However, if you have irreplaceable or expensive equipment that requires using VGA analog video, you'll find it useful to know its functionality. 

 

Typical VGA cables have a high-density fifteen-pin (HD15) connector on each end, using a combination of mini-coaxial cables and straight or twisted pair conductors to carry a video signal. VGA does not include audio support like HDMI® and DisplayPort cables do.

 

What do these terms mean? VGA stands for Video Graphics Array. As video display equipment that used the VGA standard became more sophisticated, manufacturers began adjusting the name of the standard to reflect the maximum resolution of the display device. For example, SVGA stands for Super Video Graphics Aray which supports a resolution of 800 x 600. As the list grew, it became easier to just list the maximum resolution rather than the letters that corresponded to it.

 

Today, there are over 20 different letter combinations referring to all sorts of different resolutions, a list of which can be found here. Most of these terms are rarely used to refer to analog video equipment anymore. And as mentioned previously, the standard itself is rapidly becoming legacy in the face of digital video standards such as HDMI®, DVI, and DisplayPort.

 

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