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Carrier-class F-connectors level the playing field

Tue, 10/31/2006 - 7:00pm
Owen Barthelmes, Director of Engineering, Amphenol Inc.; Steve Lampen, Multimedia Technology Manager, Belden Inc.; and Bill Spink, Connector Engineering Manager, Trompeter Electronics

One of the cable industry's biggest challenges to profitability–as in any business that's not a monopoly–is customer churn. As the telcos crank up their IPTV offerings and direct broadcast satellite (DBS) moves to next-generation services, customers will have more choices than ever for video, data and voice services. And who would have predicted the surge in the telcos' DSL business at the expense of cable modem service?

Cable operators have reason to be encouraged about their competitive position. According to the University of Michigan's American Customer Satisfaction Index study released in May 2006, cable companies are improving their performance in satisfying their subscribers. Comcast and Cox Communications actually scored better as telephony providers than they did as video suppliers (1).

Meanwhile, findings from J.D. Power and Associates' 2005 and 2006 Residential Cable/Satellite TV Satisfaction Study corroborates this trend, but also reveals the impact of DBS competition. Fifty-eight percent of households only subscribe to cable service–down from 60 percent in 2005, 62 percent in 2004 and 66 percent in 2000. Meanwhile, twenty-nine percent of households only subscribe to DBS, up two points from 2005 (2).

Are today's cable networks "carrier class"?

As cable operators equip for the hotly-competitive triple play future, much attention is being focused on boosting their high-capacity backbone infrastructures. Some are even linking their backbones across markets to bypass the public switched telephone network (PSTN) for voice and data.

They (and the telcos) are also focusing near-term buildouts on correcting the huge data rate mismatch between the backbone, the capacities of internal networks for commercial (and, increasingly, residential) customers, and the "last mile" infrastructure that connects the two.

But unlike the telcos, current cable networks have a physical layer weakness that hinders their ability to deliver true "carrier class" service, at least in the residential portion of their network "edge." This weakness is the continued use of legacy pinless (also called "feed-through") F-connectors to interconnect in-home appliances like DOCSIS cable modems, multimedia terminal adapters, digital set-tops, and other customer premises equipment.

The technical downside to the pinless F-connector is that the cable center conductor was not engineered to withstand the environment outside the cable dielectric, so it corrodes very quickly.

There is new lab test evidence that illuminates the vulnerability of the legacy F-connector design to corrosion from environmental factors. As cable moves into higher data rates, VoIP, and digital television delivery, signal degradation caused by this corrosion will introduce unwanted attenuation and impedance mismatches in both directions of the network that will adversely impact user experiences.

Porosity–the corrosion culprit

Independent test and research laboratory Contech Research conducted a test in May 2006 to determine the magnitude and severity of porosity and other types of imperfections present on electrical contact surfaces (3). Five conductor samples were tested: three gold-plated center posts of the type used in high-reliability connectors, one beryllium-copper center post (cut and flared to expose inner and outer surfaces), and one segment of standard RG6 coaxial drop cable with the cable end stripped to expose the center conductor.

The test was sponsored by Trompeter Electronics, a manufacturer of RF and microwave interconnect products. Trompeter also supplied the test samples.

First, each of the five test samples was ultrasonically cleaned after test lead attachment using Contech's six-step DI water cleaning procedure. Next, nitric acid was placed inside a test chamber to saturate the atmosphere within. The samples were then placed inside the test chamber and exposed for approximately 75 minutes to simulate and accelerate the environmental factors that cause corrosion. After exposure, the test samples were removed from the chamber and oven-dried at 125 degrees C for 10 to 15 minutes.

Results

Figures 1a through 1e show the comparative visual evidence of corrosion across the five samples. Sample E–the bare wire conductor–shows the heaviest evidence of corrosion, while two of the gold-plated pins showed no evidence, and the third mild to moderate evidence of porosity.

According to the Contech test report, "The presence of these areas [of corrosion]... result from base metals [copper, beryllium] or underplate exposure [from insufficient gold plating thickness]. These corrosion products in turn may...spread across the [entire] contacting surface...[which] can result in electrical degradation."(4)

While most cable operators have upgraded to the compression-type of F-connector for the customer drop and within the customer premise, enabling more secure physical connections to network interfaces and video components, many of these connectors still employ the bare-wire center conductor design, so the risks of contact corrosion and performance degradation remain.

Both cable and connector manufacturers are addressing the need for improved corrosion protection in the customer drop. Belden, CommScope, and other providers currently offer drop cable with dry-water-blocking, gel-water blocking, and non-permeable jacketing. But the exposed bare wire conductor in these cables is still vulnerable to environmental factors. All we do with corrosion protection does not address the center wire connection. So any wire that's hanging in the open air is going to corrode; it's not designed for that.

Belden did offer cable with a treated copper center conductor for corrosion resistance, but it was discontinued due to lack of demand.

Deployment of high reliability "carrier-class" F-connectors can eliminate the vulnerability. Connector manufacturers with strong track records of long-term applied engineering for demanding applications (ADC, Canare, and Trompeter, to name a few), have developed field-terminable F-connectors that have the same design features as their "best-in-class" products–a fixed-pin center conductor with 30-millionths of an inch of plated gold, an under-plate of nickel in the connector body to halt copper piping/migration over time, and fully enclosed high-frequency dielectrics like PTFE.

The engineering case for upgrading

But how can we expect to implement change in a mature industry that does not yet admit the need to improve itself with regard to the physical layer–the drop cable or the F-connector? A network engineering practice worth considering is one used by the telcos: include connector specification in network engineering decisions.

Cable operators have crossed many of the hurdles to delivering service comparable to the PSTN through implementing DOCSIS, PacketCable NCS, and lifeline service requirements. It is truly in operators' best business interest to elevate the issue of upgrading the customer drop to carrier-class reliability in the network engineering agenda.

Continued deployment of the pinless F-connector also has implications on the network equipment side. The practice of using the coax cable's center conductor as the connector pin forces jack manufacturers to accommodate a wide range of center conductor sizes. This is bad for RF performance. And as the cable industry rolls out the higher-level DOCSIS protocols, the current pin/jack designs will simply not perform at the higher frequencies/data rates. Transport technology will force the interconnect issue to a critical stage–the F-connector issue must be addressed if cable operators are serious about DOCSIS 2.0 and 3.0 deployment.

Correcting the customer drop vulnerability with corrosion-protected cabling and carrier-class F-connectors is a relatively minor investment compared to the cost of lost subscribers. Carrier-class F-connectors will cost more than today's compression-type connectors–perhaps as much as 10X.

But this investment would quickly return benefits from improved quality of service (QoS) and reduced operating, servicing and maintenance costs (service calls and multiple connector purchases) at a time when competitive pressures on the cable industry are intensifying to unprecedented levels.

As the cable industry builds for the future and becomes a self-contained communications network independent of the PSTN, setting a priority to invest in bringing the last mile up to carrier class standards will transform what is now the "weakest link" into an infrastructure that's more than ready to handle the exciting and profitable suite of broadband services for which consumers and commercial customers are clamoring.


Notes

1. cedmagazine.com, 5/16/2006.

2. J. D. Power and Associates Press Releases, 8/17/2005 and 8/16/2006.

3. Contech Research Test Report #206129, Porosity Testing, Gold Plated Contacts, May 10, 2006, page 7.

4. Ibid., page 7.

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