Craig, I'm curious to know about the construction of the RG-6 cable that you used for your test?
Was this just braid shielded? And if so what was the shield coverage? Was there any foil over the dielectric, and if so was that foil bonded to the dielectric or just folded? Good quality RG-6 cable will have a polyfoam dielectric. Over that will be a foil covering. This foil will be bonded (glued) to the dielectric and overlapped along the seam. You can tell this because you can't peel it back if you strip away the outer jacket and braided shield. If it's loose or the seam opens, it's pure junk. Then over the top of the foil should be a shield of 98% coverage. This will be easy to see by eye. If you can see through the braid to the foil or the dielectric if there is no foil, i.e. the weaves of the braid are open. It's junk. After that, if it's overhead RG-6 there will be a black vinyl jacket and generally a single messenger wire. This is designed to support the weight of the cable as it hangs in the air. This is generally called "figure-8" cable, because of the way a cut cross-section looks. If it's designed for underground use, there will be no messenger, but there will be a sticky flooding compound between the braid and the jacket. This is designed to keep out water should the jacket get nicked. The jacket of direct burial cable is generally thicker too. You'd be surprised at how much junk CATV cable there is out there. I always strip back the end of anything I'm going to buy if I don't already know the source and examine it visually. Additionally, I always place a ferrite choke over the outside of the cable at the termination end as well as the receiver end, to choke off any common-mode currents on the outside of the shield. As to quad-shield cable, the additional shielding effects of this may be offset by the fact that's most of it is not designed for outdoor use. Connectors are more difficult to install, though not by much of you have the proper tools and connectors. As to connectors, what did you use on that RG-6 cable you tested with? Was this a standard 1/4 inch cable prep (stripped with a calibrated stripper tool) and the foil left intact to fit inside of the connector barrel, then the shield fanned out symmetrically and crimped using the approved crimping tool for the connector used? This varies according to the connector manufacturer. The problem with any balanced feedline is always line-balance. Since the electric and magnetic field of the signals extends outside the physical area of the twisted pair, there will always be interaction between pairs within a CAT type cable. You would need far more spacing between pairs than is available in the CAT cable design to prevent interaction between pairs. Additionally, laying the cable on the ground or near to conductive surfaces will also upset the line-balance (for UTP cable.) And this prevents the common-mode rejection of signals common to both wires of the twisted pair from canceling completely. Shielded CAT cable is a different animal, outside effects being much less, but the inter-pair coupling is still an issue. Anyway... I'm just curious about the test setup. TIA Rick Kunath _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
