Low Loss Coaxial Cable for Wireless Applications

June 26, 2013 at 10:00 AM

 

Closeup of Low Loss Coaxial Cable Stripped to Show Components

Even in a wireless network, cables and wires are still used to connect components together (access points to amplifiers, amplifiers to antennas, etc). Each component needs cabling to interact.

 

If you are a wireless engineer and need to interconnect components, chances are you are using low loss coaxial cabling. While 50 Ohm RG-style coax is sometimes used, the attenuation is usually too much for any length over just a few feet. This is where low loss coaxial cable comes in.

 

 

Coaxial Cable and RG-Style Coax

 

All coaxial cable works the same way: the signal is run over two "axes" (thus the name). Coaxial technology is one of the oldest signal cabling types, and is still used today for a specific reason: it is robust and can carry a signal very well over a long distance. In general, the thicker the cable, the less "loss" or attenuation of signal there is over the length of the cable.

 

The original standards for coaxial cable were set forth by the US military. These cables used the term "RG" (for "Radio Guide" or "Radio Government") followed by a number to designate the standard. This worked well at the time, but as technology became more and more utilized in commercial and non-military applications, the restrictions of the standard became less rigid (to the point where RG316, for instance, may have very different properties today depending on who manufactures it).

 

 

Times Microwave LMR® Cables

 

No matter who makes the RG-style cables, they have one fundamental problem: the signal degrades over the length of the cable until it is no longer useable. For shorter use in labs or machine-to-machine applications, this is not a problem. But in wireless applications, the signal integrity up until it is broadcast through the antenna is critical.

 

For that reason, Times Microwave Systems developed a low loss version of coax that it branded as its LMR® series coax. The newly-engineered solution offered far lower loss and better RF shielding, making them a much better choice for wireless systems than the RG styles.

 

Outside of Times Microwave Systems' product (the term LMR® refers specifically to Times Microwave Systems product and is trademarked for their use), several other companies now offer low-loss coaxial cables. These generally follow a similar naming convention as what Times Microwave Systems uses: a three-digit "series" number that refers to both the thickness of the cable and the low loss properties.

 

For instance, 100-series low loss coax is thinner and has greater loss than 200-series, which is thinner and has greater loss than 400-series, etc.

Diagram of most common low-loss coaxial cables

Note that with thicker cable factors such as cable weight and flexibility must be considered. However, there are now ultra-flex versions of thicker series like the 400-series that offer similar loss characteristics but are far more flexible.

 

Quick note: L-com has been manufacturing high-quality coaxial cables and components for over thirty years.
 

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.
 

Tutorial on Wireless Networking

June 12, 2013 at 10:00 AM

 

Wireless network antenna and devices

Entire cities and even countries are looking into ways to expand communications access for their residents as the Internet has shifted from a luxury to an imperative. The most promising solution: wireless networking.

 

Why? Wireless networking allows a non-physical (well, at least non-cabled) connection to a wireless LAN (WLAN) and onto the World Wide Web for users. So what are you waiting for? Cut the cord!

 

Be mindful of this though- issues such as network and band congestion, security, signal range and propagation, power demands, and more make WLANs tricky to implement for all but the most informed network engineers and IT professionals. Yet there's no stopping this technology in its rapid advance, with solutions such as distributed antenna systems (DAS) and MESH networks beginning to show promise. For you to get started, here's a basic wireless tutorial on terminology and concepts.

 


Wireless Standards

 

Radio frequency signals can take a lot of different forms, so in order for devices made by different manufacturers to communicate, the IEEE has provided several standards including the mainstay for wireless Ethernet: 802.11.

 

The 802.11 standard specifies the band and IP protocol used to transmit data, and provides guidelines to maximize the speed of transmission. 802.11a, for instance, uses the 5Ghz band and can typically transmit at speeds up to 54 Mbps in shorter ranges. 802.11b, 802.11g, 802.11n, and the new 802.11ac all use various methods to increase the speed and range. The latest IEEE wireless standard, 802.11ac boasts transmission speeds of up to 1 Gbps!

 

Each standard typically requires wireless routers, access points, and other transmission equipment to match its designation, though there are many that can operate in multiple standards (such as routers that are 802.11b/g/n compliant).

 


Wireless Bands

 

In attempt to maintain order within the entire radio frequency spectrum that is available to us, the FCC and other global communications standardization organizations have designated or set aside specific ranges of frequencies for specific uses. We call these "ISM bands". ISM stands for industrial, scientific and medical to denote where these frequencies are used.  ISM bands (specifically the 2.4 GHz and 5 GHz frequencies) are also used in commercial wireless networks. 

 

Typically access points, antennas, and amplifiers all use either the 2.4 GHz band, 5.8 GHz band, or both for WiFi. Other ISM bands have been set aside for things like cell phone use, RFID chips, emergency/municipal use, and military use.

 


Wireless Security

 

As mentioned previously, one of the big emerging issues with wireless networking is security. Without a physical cable that can be plugged and unplugged, the only method to control who can do what on a network is to build it into the software and protocol. That means it is critical to set up a wireless network with appropriate security measures and to be aware of the security status of any network you connect to.

 

For most small networks, methods such as WPA, WPA2, or WPA-PSK allow the safe identification of nodes that should be allowed on a network with passwords and other controls. Wireless routers can also use access passwords to allow administrators to adjust or update security features as required.

 
If you have questions about a wireless project or application, contact L-com's technical support line for a live response and expert advice!
 

Cat 6 Shielded vs. Unshielded

June 5, 2013 at 10:00 AM


Category 6 cable with drain wire

Category 6 or Cat6 Ethernet cable is designed to provide up to 1 Gbps Ethernet transmission, and is required for 1000 Base-T style networks. However, the choice to use unshielded twisted pairs (UTP) or shielded (or screened) twisted pairs (STP or ScTP) depends on the location of the installation.

 

Typically, the shield is only required in cases where the cable is run through an area of high electro-magnetic interference or radio frequency interference (EMI/RFI), such as output by strong power lines, motors, magnets, and radio antennas. Outside of these situations, the shield does not help provide a faster or clearer signal, and can add more problems than it solves.

 

Pros and cons 

 

Without a shield, Cat 6 UTP cable is already resistant to minor and typical forms of EMI/RFI, such as having a fluorescent light or small motor nearby. In these cases, you should always run the cable at a 90° angle to the source of the interference in order to minimize exposure. Otherwise UTP is cheaper, lighter, and just as effective as STP.

 

If you need STP cable, you have to remember that the shield itself must drain, otherwise EMI/RFI can build up on it and degrade the signal inside. Drainage is typically done at the connection site by using a shielded coupler or jack that is connected to ground.

 

Also note that the weight of shielded cable, while not very heavy, can be significant if you are running multiple cables in an area. In some cases, heavy cabling run above a ceiling or behind a wall has caused collapses and structural damage over time.

 

Quick note: Visit L-com's Ethernet Product Center for a huge selection of common and hard-to-find Ethernet cabling solutions, including shielded, harsh-environment, special jacketed and more.

Picking the Right Antenna for Your Application

May 29, 2013 at 10:00 AM

 

How-To 

 

A log periodic antenna mounted on a pole or mast

If you are new to wireless technology, the multitude of antenna shapes, sizes, styles and gains can be bewildering at first. Will you need a dish antenna, a grid, a Yagi or just a rubber duck?

 

Fortunately, by following a few rules of thumb, you can get a hang of the different styles and the applications they fill. It starts with a complete survey of the area where you need coverage: its shape, size and obstructions found within it. With these details on hand, you'll need to consider the following factors:


 

Beam Width


One of the key differences between antenna styles is the "beam width" and direction. In general, the narrower the beam width the more powerful the signal is in a particular direction. That's not to say Omni directional antennas are weak, but merely that the signal strength is spread in a different way (which may or may not be appropriate for your application).

 

Read this article for more information on signal gain patterns and wireless network design.

 

Vertical and horizontal beam patterns
Beam Pattern of a Log Periodic Antenna

 

 

Antenna Polarity

 

Another aspect of antennas to keep in mind is the polarity. While wireless signals travel, they move as a wave. Just like ripples on the surface of water, waves that move in the same direction cancel each other out. Waves in different directions do not. In a similar way, too many antennas set up in a vertical polarization in an area can cancel each other out, resulting in extremely poor signals.

 

In the case where a lot of wireless signals in the same band may be required, setting up antennas with different polarities can improve the performance of each signal. In some instances, you may want to set up "dual polarized" antennas, which include both vertical and horizontal polarities. These and other types of polarities (such as "cross polarized" and "circular polarized") can improve the strength and distance of signals in multiple ways.

 

This article offers some great information on antenna polarization.

 

Antenna Polarization Diagrams
WiFi Antenna Polarization Schemes

 

 

Antenna Gain

 

The final consideration for choosing your antenna is antenna gain. Measured in decibels (dB), it is commonly written as a number followed by "dBi" (the "i" at the end is for "Isotropic", and indicates that the number is relative to an imaginary, "perfect" dipole radiation). In general, the higher the dBi the stronger the signal in whatever direction it is going.

 

While it may seem tempting to simply buy the antenna with the highest gain for your beam width and polarization, it may not be relevant for your application. You should seek a dBi relative to the size of the space that the signal needs to cover. In many cases, a high gain will provide poor coverage closer to the antenna and better coverage further away.

 

For instance, setting up an Omni directional antenna in the center of a small cafe would require a smaller gain. If you use an antenna with too large a gain, people using devices in the street outside of the cafe would have better signal than those in the cafe itself because the total signal would be stretched.

 

This article explains why too much gain is a bad thing.

 

Small gain antenna used in 300-foot courtyardLarge gain antenna used in 1000-foot courtyard
An 8 dBi Omni directional antenna is more appropriate for a 300' space in a cafe courtyard than a 14 dBi antenna.
 

Quick note: L-com's technical resources section has tons of helpful information for the WiFi newbie or established expert alike. Also, for help selecting an antenna, try the Antenna Product Wizard.

 

© L-com, Inc. All Rights Reserved. L-com, Inc., 50 High Street, West Mill, Third Floor, Suite 30, North Andover, MA 01845