Articles and whitepapers

Product Article: Bonded-Pair Category Cable (2/9/2009)

By Graeme Lewis, Maser Communications (UK)

We all know that not every application and installation is ever exactly the same, especially within the domestic and commercial markets, depending on the type of signals supported, the critical nature of the information transmitted and the overall attributes of the environment. We all just need a little more in the way of performance headroom, plus of course, peace of mind.

As more companies subcontract the cable installation, often into property where you have to compromise between an ideal dedicated cable management and the confines of the application, we still need to ensure that the cables are performing at the same level as specified by the manufacturer.

To ensure data integrity on category-type cables, Belden developed bonded-pair technology. Belden bonded-pair cables feature a patented design that bonds the individual conductors along their longitudinal axis to guarantee extremely uniform spacing within each twisted pair, and this technology offers a number of advantages to you and your customers.

Physical stresses

Stresses applied to cables when manipulated will change the physical structure of a non-bonded-pair cable. When cables are squeezed and bent during the installation process, the majority of the pulling force is distributed to the pairs of the cable. The pairs must withstand this force despite being tugged around bends and corners - while, ideally, maintaining a consistent centricity. Furthermore, any kink in the cable also changes the relationship of the conductors of a pair. For these reasons, the electrical properties of a non-bonded-pair cable can degrade over time.

When the rigors of installation cause gaps to occur at multiple points along a twisted pair, the distance between conductors, or the conductor-to-conductor centricity, is altered. This creates increased signal reflection and noise interference that can degrade network performance.

Noise can invade a non-bonded pair (left) at the gap point. Because bonded pairs (right) do not gap, they have a greater immunity to noise.

Because of the robust design of bonded-pair cables, concerns about stretching and bend radius are virtually eliminated. Bonded-pair cables boast significantly higher maximum pulling tensions and tighter bend radii over the recommended guidelines to accommodate real-world installation issues. Thus, the electrical performance of bonded-pair cables experiences little change over time and use. The cables maintain their integrity and therefore ensure the reliability of the networks that depend on them.

As an example, a Belden bonded-pair cable was flexed by a fourteen foot long C-track for over a year and a half. After 10 million flexes, the cable still exhibited performance that exceeded the TIA standard.

Noise interference

Ambient EMI/RFI (electromagnetic interference/radio frequency interference) environments can induce noise onto signals being transmitted over twisted-pair cable. This can degrade overall performance by making it more difficult for the active equipment to distinguish between the noise and the true signal.

Belden bonded-pair cables provide improved balance performance since their superior transverse conversion loss (TCL), capacitance unbalance and resistance unbalance result in less modal conversion. This means that the cabling infrastructure is less susceptible to EMI/RFI in noisy environments.

Bonded-pair cables maintain their centricity and symmetry along the length of the cable, so noise from outside sources is significantly reduced.

Return loss

When gaps form between conductors in a pair, it can create an impedance mismatch that causes portions of a signal to be reflected back towards a receiver, which is measured as return loss. At low frequencies, return loss is a minor effect, but at higher frequencies, it has a much more significant impact. With applications such as 10Gb Ethernet operating at 500MHz and broadband video operating up to 860MHz and higher, return loss is a key consideration.

Belden bonded-pair cables avoid those potential gaps, and so exhibit far better return loss performance characteristics following installation, making them ideal for high-frequency applications.

Service loops

To simulate the effects of service loops on cabling performance, cable samples from various manufacturers were tested in permanent links without being subjected to any stress. Service loops were then added to those links without violating any TIA/EIA installation guidelines.

When the links were tested again to identify any changes in performance, the links with Belden bonded-pair cables exhibited little change in return loss performance, while the non-bonded-pair cables' return loss values degraded significantly, as illustrated in the chart below.

Test showing by how much competing cables passed or failed a return loss performance test before and after having had a service loop added.

Conclusion

Cables will accommodate a level of handling as specified by the manufacture, but these recommendations are often abused due to commercial pressures. It is therefore reassuring to see a manufacturer analysing an area of concern and providing an innovative solution to cope with the demands placed upon contractors and system integrators to ensure the completed commissioned system will give the customer the required performance from the start, and can be reused if a reconfiguration or upgrade is required.

Bonded-pair cables maintain their centricity and symmetry along the length of the cable, ensure that noise from outside sources is significantly reduced, and are ideal for HD video applications where return loss is a key consideration.

Belden bonded-pair cables also have the ability to handle being continuously coiled and uncoiled, ensuring a robust and reliable infrastructure that will inevitably reduce service costs for years to come, and ensure complete customer satisfaction.

Graeme Lewis is the General Manager of Maser Communications (UK) Ltd. He would like to thank Steve Lampen from Belden for his help with this article. Maser is an international specialised distributor of cables and connectivity, and has been a Belden partner for over 25 years.

www.masercomms.co.uk