Monthly Archives: April 2020

Dealing with Impedance Mismatching

When selecting coax cable or certain types of coaxial connectors and adapters there are a variety of factors to consider such as jacket type, shielding, and loss.  Today we want to focus on impedance, specifically what to do if you encounter differing impedances.

In coax, there are two categories of impedance 50 Ohm and 75 Ohm.   Ohm is the measurement of electrical resistance.  The physical properties of the cable determine if it's impedance.  The hallmarks of 50 Ohm coax are high power handling and low attenuation and are used in RF applications.  75 Ohm coax is designed for low power, signal transmission efficiency, which is typically used in audio/video applications.

An easy-to-overlook aspect of cable choice is impedance.  In alternating current (AC) circuits, impedance (measured in ohms) represents how effectively voltage may be transmitted through the cable, before meeting the counterforces of resistance, inductance, and capacitance.  In very general terms, a low impedance rating indicates that the cable is designed to transmit a higher degree of power.  Cables rated for higher impedance, on the other hand, are often more appropriate choices for data applications that prioritize signal coherence above high voltage transmission.  

The problems begin when a cable with one impedance rating is coupled to a device with a different one.  Called impedance mismatching, this creates a situation in the circuit where only part of the intended voltage is reaching the load.  The rest rebounds back through the cable as standing waves - a phenomenon called reflection - which in turn creates echo problems for the signal still passing through

MPO Fiber Optics

As the need for bandwidth speed outpaces the capabilities for physical expansion, networks are evolving by offering higher density higher throughput solutions. This allows for increased data rate performance without having to invest in new physical locations. MPO cables provide high-density termination capabilities and are an ideal choice for delivering the fastest link and enabling high-speed interconnects.

Multi-fiber push-on connectors (MPO) are multi-fiber cables terminated in a single connector. They are typically available in 8, 12 or 24 fibers and are common for data center and LAN en- environments. They ease cable management and allow faster deployment in duplex 10 Gig fiber applications.

You may also see the term MTP used interchangeably with MPO connectors, but the term MTP is a registered trademark of US Conec to describe their brand’s offered connector. Moving forward in this article, we will be using the term MPO, which offers the same benefits.

MPO cables can be broken down into three categories: MPO Patch Cables, MPO Conversion Cables, and MPO Breakouts. Each type of cable is available in numerous configurations including standard, riser or LSZH jackets and OM3, OM4 or OM5 modes.

Patch Cables

MPO cables are all about high speed and high density, which have been designed for reliable and quick operations in data centers. Depending on h