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Bulletproof Your Drop
Build It Right the First Time
By Ron Hranac

• Coaxial drop cable advantages
• Preparing for new technologies
• Cable preparation
• Crimping
• Tighten things up
• Keep the water out
• Put it all together
• F-Connectors, Step by Step (Photos)
• Bottom Line

	Ron Hranac

Still, the lowly subscriber drop generally is the weakest link in most systems. Its responsible for up to 70 percent of subscriber service calls, and in two-way systems as much as 95 percent of reverse path problems originate in the drop.

In some regards, the drop is the most labor-intensive part of an operating cable system because its arguably the most "handled" part of the system. We connect it, disconnect it and reconnect it. We add new outlets, remove old outlets and relocate existing outlets. We tighten loose connectors, replace damaged parts and add new parts. The wind blows it around, and trucks, snow, ice and tree limbs knock it down. The subscriber moves it, tampers with it, drives fence posts through itand then the dog chews it.

And through all of this, the drop has to transport conventional analog TV channels, FM radio, digital audio, digital video, and data for cable modems and interactive services. The subscriber drop, despite its perceived shortcomings, remains the most cost-effective broadband pipe into the home, whether its content is analog or digital.

Thus, the drop must be transparent to the transmission method used, be capable of two-way operation from at least 5-1,000 MHz, and do so over an expected 10- to 15-year service life or longer.

Coaxial drop cable advantages

When thinking about the advantages of coaxial cable for providing broadband service to the home, one comparison that invariably comes to mind is the telephone companys copper twisted-pair. Of course, there is also fiber, but fiber to the home isnt yet practical or cost-effective.

Recent technology developments in the area of xDSL (digital subscriber line) allow very high data rates to be carried on existing telephone wiring. xDSL is known as a fast-copper technology that includes asymmetric digital subscriber line (ADSL), high-speed digital subscriber line (HDSL) and very high-speed digital subscriber line (VDSL).

VDSL, for instance, can provide data rates from 13 Mbps to 51 Mbps. This is impressive, considering that the twisted-pair originally was intended to support only voice communication, which requires a nominal 3 kHz bandwidth.

However, twisted-pair pales in comparison to coaxial cable. Given that a coaxial cable subscriber drop can easily transport 5-1,000 MHzthat is, 995 MHz of bandwidththen the usable capacity of coax becomes apparent. That much bandwidth can carry the equivalent of more than 165 TV channels, each 6 MHz wide.

Assuming the use of 64-QAM (quadrature amplitude modulation) digital modulation on each 6 MHz channel, more than 4.4 Gbps could be transported on a single coax. More complex digital modulation schemes will allow an even larger amount of data. In reality, cable TV coaxial cable can be used well above 1,000 MHz, so its theoretical data capacity is greater still.

Another coax advantage is its ability to provide a consumer-friendly interface. Millions of cable-compatible TV sets and videocassette recorders (VCRs) can be connected directly to the subscriber drop cable, and the addition of a set-top box, which has a coax input and output, takes care of conditional access when necessary.

The point of this is that a coaxial cable subscriber drop that has been installed correctly using quality components and good workmanship is very capable of delivering video, voice, data and much more.

Preparing for new technologies

Two key elements critical to the deployment of new technologies are system quality and reliability. Achieving these requires use of the previously mentioned quality components and good workmanship, plus appropriate tools for the job. Lets look at each of these as they apply to the subscriber drop.

Components: One of the first places to start when selecting drop components is the cable itself. At the very least, all cables must be bonded foil types. One-way systems can get away with conventional foil-braid cables, but the braid needs to be four-end braid. Two-way services usually require extra shielding for ingress resistance in the 5-40 MHz spectrum; tri-shield or better is recommended.

All of the major cable manufacturers offer optional corrosion-inhibiting compounds, which you need to use for extra insurance against moisture damage. Of course, all underground cables must use flooded (filled) cables. And all overhead drops must use messengered cable, regardless of lengthno exceptions.

Passives are another story altogether. For years, weve generally used the cheapest drop passives available, but these simply arent good enough in most cases.

One particular splitter design is fairly common, but it does not provide good RF shielding. Its construction is straightforward: A thin sheetmetal plate is used as the cover (usually on the back of the splitter), and its glued to the splitter body.

The problem with this design is that during assembly the glue gets under the metal cover, preventing good metal-to-metal contact and compromising shielding effectiveness. Youre better off spending a few cents more for splitters that have their covers crimped on, soldered or press-fit before the bead of weatherproofing is applied.

Hardware may seem like a no-brainer, but a closer inspection of whats available will show that some is very good, and some isnt. For long-term reliability and drop longevity, pay a little more for the better hardware.

In terms of hardware, cable attachments occasionally are overlooked. At one time, installers used staples widely, but you must avoid them like the plague. If a staple penetrates the cable jacket, rapid deterioration of the shield will follow. A staple through the cable will result in a direct short. Instead, use clips that are sized to fit the cable, and be sure to space them unevenly. Dont forget other important drop hardware: ground blocks, weatherproofing (especially weatherproofing), lockboxes, wallplates and so on.

The last component is responsible for up to half of all drop-related service calls. Its the F-connector. More specifically, its the way the connector is installed that causes the majority of problems. Over the years, manufacturers have designed a variety of premium sealed connectors to reduce craft-related problems, while providing a more reliable and better quality interface. Here, too, I suggest you spend a little more up front for better connectors to avoid expensive callbacks in the future.

Workmanship: The very best drop components are of little value if they are installed incorrectly. By far, poor workmanship is the biggest cause of controllable subscriber drop problems. Loose and improperly installed F-connectors, lack of weatherproofing, cable bent too tightly around corners, sloppy cable routing and so forth result in callbacks, service calls, signal leakage, poor reception and shortened drop life.

The only two ways to reduce craft-related subscriber drop problems are training and quality control.

One of the best places to start with installation training is the Society of Cable Telecommunications Engineers Installer certification program. It provides a broad overview of the subscriber drop installation process and includes a combination of written and hands-on exams. Some companies have adapted this program for system-specific training.

Other good sources of training include courses from the National Cable Television Institute, Cleveland Institute of Electronics, vocational-technical schools, and night and weekend classes at local colleges. Many industry manufacturers have product-specific training programs available.

As we move toward the deployment of more advanced services, training programs will evolve along with these services. The installer of the future will be expected to know traditional installation techniques, plus data communications and networking, personal computer (PC) operation, basic telephony, and advanced home entertainment equipment operation.

The second part of good workmanship is quality control. An effective installation quality control program will provide a means to randomly inspect 5 percent to 10 percent of all installations, including those performed by both in-house and contract installers. Positive feedback is essential for good work, and when problems are identified, appropriate steps can be taken to remedy the situation. Generally, this will involve additional or refresher training.

Tools: Gone are the days when a pocketknife and pair of crimpers were all you needed to install connectors. The critical nature of some of the signals carried on cable systems makes them highly susceptible to loose or improperly installed connectors that can cause ingress, intermittent connections or poor return loss.

Doing the job right really requires a suite of tools: one for cable preparation, another to crimp the connector and one to correctly tighten the connector on the mating interface. Furthermore, the tools must be the right ones for the particular connectors and cable being installed. Older, worn out tools must be repaired or replaced.

Be wary of using low-cost imported "clones." Many of them do not have the same dimensional tolerances as the proper tools, which will affect the quality of the installation.

Cable preparation

There are several sizes and varieties of drop cable in use today: 59 series, 6 series, 7 series (sometimes referred to as 611 series) and 11 series. Available shield configurations include bonded foil-braid, tri-shield and quad-shield. Each of these requires the right connector to fit a particular size of cable. In some cases, depending on the connector manufacturer and specific type of connector, many connectors may be available for a given size cable, mainly to accommodate different shield configurations.

Older design one-piece "conventional" hex-crimp connectors technically require a two-step cable preparation process because the braid must be folded back over the jacket prior to trimming the dielectric and installing the connector. Conventional hex crimp connector cable preparation involves removing 3/8-inch of the jacket, folding the exposed braid back over the jacket, removing 1/4-inch of dielectric, then installing and crimping the connector.

Most newer connector designs have adopted the so-called quarter-quarter prep, which allows a one-step cable preparation process. This simplifies cable preparation and connector installation. Use of the right cable preparation tool ensures consistency from one connector to the next.

The majority of drop cable preparation tools control the jacket, braid and dielectric cuts with preset blades. This leaves little room for error. When looking for a tool, choose one made from strong lightweight materialsthe last thing an installer wants is something heavy added to the tool pouch. For convenience and safety, consider tools that have replaceable blade cartridges.

So just what can happen if the cable isnt prepared correctly before connector installation? Potential problems include:

1) Too much braid cut off: Increased signal leakage and ingress; decreased axial pull (it should take at least 40 pounds to pull a crimped connector off of the end of a piece of drop cable)

2) Incorrect dielectric length: Poor return loss

3) Incorrect center conductor length: Excessive signal loss if the center conductor is too short; mating interface damage if the center conductor is too long

4) Center conductor scored: Possible signal loss at higher frequencies

Crimping

Here, the right tool for the job is critical. Ive seen connectors crimped with pliers, the wrong size hex crimp tool, worn-out crimpers, and in some cases not crimped at all. Almost all premium connectors (Digicon, EX, EZF, Push & Lock, TAC and so on) require a special crimp tool. Make sure you are using a tool that was designed for a given connector.

While its pretty obvious that a hex crimper wont work on a Snap-N-Seal connector, what may be less obvious is the size of hex to use on a hex crimp connector. If you try to use a .360 hex on a connector designed for a .324 hex, youll be able to pull the crimped connector off the cable by hand. Going the other way, using a .324 hex on a connector designed for a .360 crimp will damage the crimp ring area of the connector. If you try to use pliers to crimp any connector, you can pretty much figure on a crushed connector and probably damaged cable.

Improperly crimped connectors can lead to signal leakage and ingress problems, poor return loss and compromised weatherproofingwhich leads to damaged cable and components and intermittent connections.

Tighten things up

Assuming youve chosen the right connector for the cable being used, prepared the cable correctly, installed and properly crimped the connector, whats next? Making sure the connector is adequately tightened on the mating interface. This requires a suitable torque wrench. When tightening the connector at the tap, ground block, splitter and other cable hardware, you need to torque it to between 20 and 30 inch pounds. The exceptions are TV sets and VCRs because their built-in connectors may twist off or be otherwise damaged by going much beyond finger-tight.

Loose connectors can be a source of signal leakage and ingress and likely will produce an intermittent connection. To ensure the correct connector torque (tightness), use a preset torque wrench.

Keep the water out

Last but not least, make sure all outdoor F-connectors are weatherproofedeven those in pedestals and lockboxes. Conventional hex crimp connectors must be protected with boots and silicone grease; premium connectors, which usually have built-in O-rings or some other weatherproofing mechanism, still need a sealing sleeve installed over the threads on the tap, splitter or ground block.

Put it all together

As I mentioned earlier, installing subscriber drops is not rocket science. Drops are arguably the most craft-sensitive part of a cable system. Choosing good components and dealing with workmanship issues are two important areas, but a common thread in all of this is use of the right tools for the job. Proper installation tools will increase productivity and ensure consistency from drop to drop, resulting in improved quality and reliability. Over the long term, you can expect fewer service calls, lower maintenance costs, better two-way performance and ultimately happier subscribers. TB

F-Connectors, Step by Step

Drop installation tools have come a long way from the old semi-circular crimper and a pocketknife. The major cable TV tool manufacturers have available quality tools that eliminate as much craft sensitivity as possible from cable preparation and connector installation. For instance, Ripley Co., manufacturer of the Cablematic line, has designed a system of tools for drop installation that includes a cable preparation tool, connector insertion tool, crimper, pocket toner continuity tester, and combination torque wrench and F-port rethreader. The following photos provide a step-by-step guide to drop connectorization using some of Cablematics tools and a premium sealed compression style F-connector. All photos are courtesy of Coaxial International.

Step 1: Squarely cut the end of the cable with a sharp pair of wire cutters.

Step 2: Next, insert the end of the cable in the cable preparation tool. This particular model features color-coded reokaceabke blade cartridges for 59, 6 and 11 series cable in the same tool.

Step 3: Rotate the tool around the cable three to five times. This will remove the correct amount of jacket and dielectric material.

Step 4: Pull the tool away from the end of the cable, exposing the trimmed end.

Step 5: If required for the particular connector being used, fold the braid back over the jacket

Step 6: Install the F-connector on the prepared end of the cable.

Step 7: Insert the cable and connector into the crimp tool. This particular tool is a compression-type crimper.

Step 8: Crimp the connector.

Step 10: Torque the connector nut to between 20 and 30 inch-pounds. The torque wrench shown is factory preset to 30 inch-pounds. A word of caution: Do not use torque wrenches on consumer equipment such as TV sets or videocassette recorders (VCRs). The connectors on those devices may be damaged by tightening much beyond finger-tight.

Ron Hranac is senior vice president of engineering for the Denver-based consulting firm Coaxial International. He also is senior technical editor for "Communications Technology." He can be reached via e-mail at .

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