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 senior director of service provider FAE for CommScope, a global leader in infrastructure solutions for communications networks. 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.

 

See all posts by this author

Comments

4 comments for "Mythbusting Coaxial Drop Cable"
Brady Hood Saturday, May 13, 2017 9:37 AM

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 12:09 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 1:10 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 2:50 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!

Add Your Comment

Please submit your comment using the form below

 
(required)