Tips on Selecting an Ethernet Media Converter

January 9, 2014 at 10:00 AM


L-com Industrial Ethernet Media Converter (DIN Rail mounting)

Fiber optic technology is taking the Ethernet networking world by storm. It is faster, completely resistant to EMI/RFI, and offers incredible distances between nodes.

 

But fiber is not quite ready for all LAN applications. In many cases it makes sense to keep a copper network intact and lay a fiber network over it. So, here we find a need in our industry for a device that will convert seamlessly between the fiber optic network and the copper network without loss of speed.

 

We call these devices Ethernet media converters.

 

 

Industrial vs. Commercial

 

Commercial Media Converters

The first consideration in finding the proper converter for your application is whether your Ethernet media converter will be installed in a commercial or industrial environment. A commercial environment would include a typical office or clean room, and an industrial environment includes places with dust, moisture, temperature variations, vibrations, and other complications.

 

We've gone over the differences between the two in regards to switches before, but the same rules apply for media converters. It is very important not to confuse industrial versus commercial converters. While an industrial Ethernet media converter can operate in a commercial environment, it costs more and generally supports features not commonly found in a commercial environment such as DC power. On the other hand, a commercial Ethernet media converter should not be used in an industrial environment as network downtime and system failure can occur.

 


Single mode vs. Multimode

 

Fiber Glass Types

There are two main "modes" for fiber optic cabling: single mode and multimode. L-com has a great tutorial and video with in-depth explanation. In general, a single mode system is more expensive, but also provides better signal strength over large distances (up to 100km or more).

 

Multimode is much more affordable and can be used in distances of up to 2km, depending on network speed and bandwidth. Again, don't confuse the two! If you are running multimode cable, you need a multimode Ethernet media converter; a single mode version will not work.

 


Fiber Optic Connector Types

 

 

Fiber optic cables have their own unique connector types. There's a good video explaining fiber connectors here. Unlike copper, fiber connectors are very difficult to install properly in the field, and there aren't many options for converting a connector type with a passive adapter (although L-com does carry ST-SC, ST-FC and LC-SC adapters, among others, on its fiber optic adapters page). It is best to match the connector type with the device so they can be easily connected and no extra loss is incurred.

 

Remember, L-com stocks hundreds of factory terminated fiber optic cables off-the-shelf. We can custom manufacture fiber cables without minimum order quantities and with very short lead times, so you don't need to re-terminate or adapt a mismatched cable.

 

 

Other Features

 

Before ordering your media converter, also consider things like mounting method (DIN rails, 19" racks or chassis, or just placed on a shelf), network speed (10/100/1000 Mbps), and how you will get power to the unit. A properly installed media converter can both future-proof and provide redundancy for your network for years to come!

 

Quick note: Installing Ethernet media converters may require other components as well, such as fiber optic cables, Ethernet cables, and racks and accessories.
 

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.
 

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.
 

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.

 

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