Introduction of Loopback Cable and How can we Create it?

What Is Loopback Cable?

A loopback cable is also known as loopback plug or loopback adapter, which is a plug used to test physical ports to identify network issue. It provides system test engineers a simple but effective way of testing the transmission capability and receiver sensitivity of network equipment. In a word, it is a connection device that is plugged into a port to perform a loopback test. There are loopback plugs for many different ports, including serial ports, Ethernet ports, and WAN connections.

Loopback Cable Type

Fiber Loopback Cable

Fiber optic loopback incorprates two fiber optic connectors which are plugged into the output and input port of the equipment respectively. Therefore, fiber loopback cables can be classified by the connector types, such as LC, SC, FC, MTRJ. These fiber optic loopback plug connectors are compliant to IEC, TIA/EIA, NTT and JIS specifications. Besides, fiber optic loopback cables also can be divided into single mode and multimode fiber loopback. To describe this item clearly, I will take LC fiber optic loopback cable as an example, which is one of the most popular cables (as shown in the following figure). The LC fiber optic loopback cables support the test of transceivers featuring LC interface. They can comply with the RJ-45 style interface with low insertion loss, low back reflection and high precision alignment. LC loopback cables can be 9/125 single mode, 50/125 multimode or 62.5/125 multimode fiber type.

RJ45 Loopback Cable

A Gigabit RJ45 loopback cable is an exceedingly user friendly cable tester. It looks like a simple plug at first glance, but the compact and rugged design makes it highly portable and usable in the tightest corners. All you have to do is to simply plug the Gigabit RJ45 loopback into the jack that you want to test or the one you are suspicious about. If the link LED on your switch is active, it means that the connection is operating perfectly. The RJ45 loopback cable will negate the necessity to carry a bulky network hub around.

How to build the loopback cable simplified?

If you are handy with building ethernet cables, the simple explanation is;
1. Redirect Pin 1 to Pin 3 and Pin 2 to Pin 6.
2. Make sure you create tight twists to account for signal interference at such a short length.

How to build a loopback cable illustrated?

Step 1. Get a pair of approximately 4 inches in length of cat 5 cable.
Step 2. Leave approximately 1/2 inch at end and start twisting, very tightly.

Note: If your fingers start to hurt, you may want to use a tool to help with the twisting. Notice how tightly wound the cable is. If the twists are not close enough the loopback will not work. Please twist to match picture.

Step 3. After twisting is done, fold cable and line up the ends. Cut if you must to line up cables. Line up the cables so that the cables are in the proper alignment to prepare for insertion into RJ-45 end.
Step 4: Insert cable into RJ-45 end. (do not crimp yet.) Remember, 1236 pins.
Step 5. Insert plastic tubing over the wire and into the RJ-45 end. Now crimp the end with a crimping tool.

Note: When you first plug in the loopback cable, wait approximately 10 seconds to get a link light. No more carrying around a hub just to get a link light.

Conclusion

All in all, If we know what a is loopback cables and know how to create loopback cables, it will bring many benefits to our work and life.loopback cables play an important role in troubleshooting in laboratories and manufacturing environments. They facilitate the testing of simple networking issues and are available at very low costs. There are many loopback cable manufactures on the market, providing single mode and multimode fiber optic loopback plugs available with FC, LC, MT-RJ, SC connectors. Fiber-Mart is one of the fiber loopback cable providers, all loopback cables are precision terminated and feature extremely low loss characteristics for transparent operation in the test environment.