Friday, October 23, 2015

"No, It's Getting-Hit-On-The-Head Lessons in Here..."

     I spent about an hour and a half tracking down a problem at work yesterday, which turned out to be all the way back to one connector away from the source, where a sub-miniature coaxial cable had apparently been damaged by rough handling, wiping out a high-definition video signal.

     In the old days, video was shipped around in RG-59-type cables, or big, fat Belden 8281.  Both of them had relatively incompressible solid plastic internal insulators.  You could very nearly hit the stuff with a hammer without harming it; you could walk on it with impunity and the normal wear and tear of being crammed into tight spots with a few score other similar cables was insignificant.

     Fast forward to 2015 -- heck, to 2005 -- and the demands of high-speed serial digital video mean we're using foam-dielectric coax, in about 0.25" and 0.125" diameters.  Kink it, bend it tight around a corner, bend it sharply at the connector or step on it, and you have killed it dead.  Crunch a tie-wrap tightly around it and it'll conk out deader'n last years Cat. 6 cable under similar circumstances.  The littlest stuff won't even withstand a straight pull of more than about 40 pounds force!  And occasionally, it lingers, expiring slowly, waiting until the least convenient moment.  Now the old-timers at work, they know all there is to know about working with coax -- if they don't know it, it's not worth knowing.  Yes, they know everything about the proper care...of RG-59 and 8281.  Foam-insulated coax, now, well, the habits of a lifetime are not easy to change.  Especially if you don't give too much of a damn. Besides, it usually works.  Until it doesn't.

     And so it goes.  Me, I never drink -- well, hardly ever -- but I came home from work last night and made a nice tall glass of Pimm's No. 1 and rose-elderflower lemonade.  I'd've made and consumed two, if I'd had more lemonade.  The mess I had to dig through was never very nice but it has somehow become exponentially worse over the last few months, and there's no way to fix it without causing considerable disruption.  I'll probably have to be the disruptor -- again.

10 comments:

Raz Raxxaffian said...

I sympathize....

Every cabling problem I ever solved always seemed to happen in the last place I looked!

As for me, a Jack with a beer back always made the pain go away...

Raz

rickn8or said...

Yes, I've started chasing gremlins at the wrong end of the run more than once. I suppose it's not any easier in a building than in an airplane.

No way to TDR it?

Chuck Pergiel said...

DIY TDR http://tinyurl.com/q5a25k5

Richard Tengdin said...

Optical fiber cables are as bad.. Cleaning up after a trade show we watched a union worker grab a 15m FC cable, coil it tightly around his elbow then take the free end and tie a nice overhand knot to secure the coil. After he left we swept about $10k in cables into the trash can...

Seems all cables are assumed to be as abuse-worthy as your basic outdoor extension cord..

Roberta X said...

No way to TDR it -- no way to even know where the far end was. I started tracing from what I thought was the source, only to discover it came from somewhere completely else, so I had to start over, at the destination, and work painfully backwards. To begin with, I didn't even have a portable video monitor, and this signal was in three different flavors, depending on where in the chain of converters one was looking.

Old NFO said...

But you found it and fixed it. You DID exactly what you're supposed to. You never gave up. Kudos to you for the effort, and yes, you'll probably have to do it again, and again...

Keads said...

Yes, coax, twin-ax, etc. were very forgiving of physical abuse if terminated properly. Good on you for fixing the issue!

Ken said...

Hi Roberta,

I'm on the receiving end of OTA television, and the wiring in the house is a mix of RG-6 previously installed by Comcast, and some quad shield RG-6 from home depot installed by me. Is RG-6 the foam dielectric fiddly stuff you're referring to? Or is that a property separate from the cable type to look out for and treat gently? Thanks!

Roberta X said...

The stuff we use is (still) a riff on RG-59 rather than -6, plus a submini that I don't know the old RG-series number for the base design. It's a little smaller in diameter than 6.

IIRC, RG-6 and relatives are made in both solid and foam core (plus some nasty weatherproof versions with sticky gunk under the outer jacket and a version with a molded-in steel carrier wire that will ruin diagonal cutters). You shouldn't step on or sharply bend any of the flexible cables but the older solid-core stuff has a relatively stiff, incompressible translucent dielectric that is fairly rugged. Foam core has a white, compressible closed-cell foam dielectric. In the latter, the solid center conductor can migrate through the foam if it is sharply bent and it is a lot easier to smash. You can check scraps of your cable and tell what kind it is.

Baseband digital video is generally less tolerant of cable faults than *any* kind of RF: my stuff breaks easier.

0007 said...

OSSM connectors and RG-144...