RF

Coaxial drop cable is the stuff of legend. Like other legends, plenty of myths develop over time about the product, its preparation and performance. I’m a huge fan of the show, “MythBusters,” so let’s bust a few drop cable myths right here.

 

Myth 1 – The denser the braid, the better the shielding.

Braid density is one factor that impacts drop cable shielding, but it’s not the only one.  Coaxial cable is both a precision radio frequency (RF) waveguide and a mechanical structure. If the mechanical structure is compromised, the RF performance will be as well.  Heavily braided cables can negatively impact shielding as the braid structure works against the bonding and tape layers during handling, installation or environmental flexure. It can also make a cable stiffer and more difficult to properly prepare for termination. Decades of engineering at CommScope have taught us that an optimized braid working in tight alignment with advanced tapes and bonding provides the best shielding under any installation and handling conditions.  Our F677TSVV-XP is just such a cable, with a 77 percent braid that outperforms 90 percent braid (and even quad shield).  

Myth 2 – LTE interference requires a different shielding design.

LTE interference is certainly a prevalent issue today, and one that is well understood by CommScope.  We see and understand best practices from both sides – wireless and wireline.  Bottom line, LTE is a potential interfering wireless signal, at a set of frequencies. The same shielding techniques that have evolved over decades protect against LTE.  

What is the biggest culprit when shielding is compromised?  Experience suggests it is the connector interface, so proper cable preparation is paramount.  Would you be surprised that there are myths about termination too?  

Myth 3 – Snip off the center conductor so it “looks right.”

Modern drop cable stripping tools are designed to provide a center conductor length of 5/16”, as recommended by the Society of Cable Telecommunications Engineers (SCTE).  Connector nuts can vary in height, so the 5/16” length may look different with different connectors.  If cut off, the conductor risks being too short, and may cause electrical anomalies during temperature changes.  Remember, drop cable is both a waveguide AND a mechanical structure.  Components can move, and 5/16” (not ¼” or “eyeballed”) is the best length to ensure solid connectivity in any temperature.  Trust your tools!  

Myth 4 – Using a connector or plier to “round out” the cable helps ease insertion force.

Argh… where do I start?  Proper tools, in good condition and with sharp, fresh blades, will produce a well-rounded cable end ready for termination.  The outer foil must be removed (and can be automatically with CommScope XpressPrep), and the braid must be folded back along the jacket in an even distribution.  A stiff plastic brush or fingertip can accomplish this. Using a metal tool of ANY sort can damage components, cut braids and lead to potential connector failure and truck rolls. CommScope has offered training and videos to assist in this procedure for decades, and we have NEVER recommended a metal tool or shortcut using anything as a tool.  

Myth 5 – I’ve been using this tool for 20 years and…

I have a screwdriver in my drawer that is bent 45 degrees. Why? I used it for the wrong purpose. I keep it to remind myself never to do that again!  The SCTE has prescribed prep lengths for coaxial cable. To achieve this prep, tool manufacturers make tools specific for the cable.  Use the right tool, with the right blade, for the job.  Are your tools 20 years old? Replace them!  Old blades, or the wrong blade, can damage the cable end. If you see braids on the ground, change the tool or blade.  Don’t allow a $2 blade to create several $100 truck rolls!   

Have you heard other myths that might put your subscriber experience at risk? Share them here, and let’s bust them all. Reliable and repeatable coaxial drop cable terminations are critical to network performance. If you avoid the myth trap, your connections can be truly legendary.

About the Author

Mark Alrutz

Mark Alrutz is the vice president of global service providers in the FAE organization for CommScope. He is responsible for technical solution sales, applications engineering, pre- and post-sales technical support, and customer training. Mr. Alrutz received his bachelor’s degree in electrical engineering and master of science degree  in management from Georgia Tech. He has been an active SCTE member since 1996. He also participates on the SCTE Interface Practices Subcommittee and the Energy 2020 program. Mr. Alrutz holds numerous U.S. patents and has been published in several industry trade magazines.

 

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Comments

6 comments for "Mythbusting Coaxial Drop Cable"
Brady Hood Saturday, May 13, 2017 1:37 PM

Hi Mark,
Great blog! I have seen wide use of tri-shield prep tool blades being used to prep quad shielded cable. The problem is that the tri-shield blade will cut the outer layer of braid away when used to prep quad. Would you agree that this practice can be problematic?

Mark Alrutz Monday, May 15, 2017 4:09 PM

Brady,
I agree, using a tri-shield blade on quad-shield cable could lead to problems. First, the blade will cut some of the outer braid wires (which we don't recommend) and second it may not properly cut the outer foil (which we do recommend).
Why these recommendations? If the outer braids are cut, the inserted connector can push them down under the jacket and block proper connector seating, not to mention the loss of that grounding connection. Second, cut braids are notorious for winding up under the connector sealing rings, and we all know how water finds every available path.
Regarding the tape not being evenly cut, if it is torn unevenly it can cause the folded braid to bunch up on one side, and the connector may be forced to insert at an angle. A connector inserted this way can catch and further damage the shield components.
Like I suggested earlier, don't let an inexpensive blade cause expensive truck rolls. Use the right tool for the job and you will appreciate the results.

Charles Robinson Tuesday, June 27, 2017 5:10 PM

Re Myth 1 – The denser the braid, the better the shielding

Hi Mark,
Couldn't help a grin when I read this, don't knock the braid too much.
Brings me back to the 60s growing up, we were using Times Wire coax as "leaky coax" (think it had something like 60% shield) to extend coverage for railroad and industrial plants etc.
Indoors we used it on 168, 450 mHz to extend coverage; for 890 MHz we used regular coax and fabricated "EESA" (Extremely Electrically Short Antennas) we screwed in connectors to give us what's touted as DAS today.

This was before Andrew came up with their version of "leaky coax", can't remember the name of the Andrew Sales rep who saw us doing that now, it's so long ago.
Today, we use Andrew's Leaky Coax almostly exclusively in Mines and other Industrial applications for high reliability "DAS", Two-Way Radios, Trapped Miner Location and other Personnel Tracking etc. running at 99.999%+ reliability.

Mark Alrutz Tuesday, June 27, 2017 6:50 PM

Charles,
Happy I made you grin.
I would never knock braid! It is a critical component in the shielding performance, particularly at lower frequencies. My point was that it is not the ONLY component of importance, and that's the myth.
Also, thanks for the walk down memory lane. DAS and leaky solutions have certainly come a long way over the years, as have all the Andrew solutions, now proudly under the CommScope flag!

Gary Thursday, October 17, 2019 7:07 AM

Mark,
You say in the post that 7451403 | F677TSVV XP NEU out preforms others. I am rewiring my home for UHD TV and I want to know which Coaxial is the performer to use for my TV's & also use for my internet? I my use a seperate ethernet for my intenet not sure, can you give me a product number so i can get the best coaxial, connectors, correct tools to cut & put the end screw ons with? Also what about splitters which are best that wont lose signal? Amp? Any other that applies that will i need to do the job corrrectly.
Thanks,
Gay

Chris Gemme Thursday, October 17, 2019 2:43 PM

Gary,

First off, thank you for reading this blog and researching with CommScope.

The best performing RG-6 type coaxial cable on the market for today’s in-home RF networks, for video and data, are the family of F677TSVV XP cables available in black, white, and neutral. It provides the highest performance of shielding available, even out performing traditional quad shield coaxial cables.

After the cable is prepped for a connector, the braid should be folded back over the jacket and uniformly spread around the cable. This not only improves the cable and connector interface performance electrically and mechanically, it makes it easier to put the connector on.

For a connector we recommend the Corning-Gilbert UltraRange GF-UR-6. There are a number of SCTE compliant prep tools on the market that work very well, like the CablePrep CPT-6590 for prepping the cable and the CablePrep Cobra360 for compressing the connector.

As for splitters, they will all lose some signal as the name implies it is splitting the signal. Split a single cable to two outputs and you lose 3.5 dB on each output leg. A four-way split would be 7 dB loss per leg. For splitter we would recommend the following CommScope parts:

CSM2G 2-Way
CSM3G 3-Way
CSM4G 4-Way

Only use an amplifier if necessary. Amplifying signal using the thought the more is always better is not relevant with RF networks. RF devices operate most optimally within a range typically of -6 dBmv to 0 dBmv. Too much power can disrupt the receiver’s ability to process the signal. In addition, not only does the desired signal become amplified, so does the noise which is very disruptive to RF networks. If you do need an amplifier we recommend the use of s unity gain amplifier which overcomes the loss of the splits in the device, so for instance if the input is 1 dB the output on each leg is then 1 dB. That part number is CSMAPDU9VPI.

Best regards,
Chris

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