Calculating Loss Budget: What it Means and How to Factor in Splice-On Connectors

To evaluate this effectively, you need to calculate insertion loss (which is signal loss that occurs along a cable). Insertion loss is also called "attenuation" and expressed in decibels (dB). It's impacted by a few factors:

• Cable length (longer lengths bring more insertion loss)
• Connection points (couplers, splitters or splices, for example)
• Differences between transmitters and receivers in active equipment

If insertion loss is 3 dB/km at the required frequency, then insertion loss will be approximately 0.3 dB for a cable length of 100 m.

From there, factor in insertion loss of the connection points in the channel. This information is based on factory testing and provided by the connector manufacturer. Currently, TIA standards state that a connector’s maximum insertion loss should be 0.75 dB. (The connectors on both ends of the channel need to be included as well.)

In terms of splices, TIA standards currently state that a splice's maximum insertion loss should be 0.3 dB. (Splice quality matters! A poorly completed splice or a field-terminated splice can increase loss even more.)

Why Calculate a Loss Budget?

Compare those results to the maximum insertion loss for your application – and don’t forget to factor in future technology that may utilize the cable. Depending on your application, there are maximum insertion loss requirements to abide by. They ensure that signals can move from one end of the cable to the other. By adding estimated average losses together, you’ll uncover your estimated total loss. Knowing this number early on in a project helps make sure that the cabling system being designed will work with the channel it’s intended to be used over. After installation, calculated loss budget can be compared to test results to ensure proper installation.

When managing a fiber loss budget, you should always leave some leeway (overhead margin) for future reconfigurations or changes.

Cable loss is typically the smallest contributor to loss budget. The largest loss actually comes from connectors. Even if you find a cable claiming to offer the lowest loss on the market, overall performance isn’t about the cable attenuation – it’s about the system as a whole.

Consider a car, for example: Would you purchase a car with a smaller engine to achieve efficiency? True, the car may offer a smaller engine than all of its competitors; however, if it's less powerful and doesn't offer the best mileage, then what difference does a small engine make? Upon closer inspection, this "value proposition" doesn't hold much value at all.

The same idea holds true with cable insertion loss. You can select a cable that offers the lowest loss, but so many other factors influence the overall loss budget - and those factors matter even more than cable attenuation.

Insertion Loss for Splice-On Connectors

When calculating loss budget, many people believe that splice-on connectors require two calculations:

1. A loss for the connector
2. A loss for the splice

In some cases, this may be true. But high-quality splice-on connectors take both of those numbers into consideration, providing one total loss number that covers insertion loss for the entire connector (including the splice). High-quality connectors that offer lower loss can be a more cost-effective way to control loss budget vs. purchasing expensive cables that offer lower loss.

Because they use a splicer, a continuous connection is created by “welding” (or, quite literally, fusing) fiber cores together – along with a factory-terminated connector end-face. The result: They offer better insertion loss performance as compared to a mechanical splice.

Want to learn more about Belden’s FiberExpress Fusion Splice-On Connectors? You’ll find what you need here!