Patrick Martin wrote: > I would think if the center connector of good coax had quad shield, > you should hardly get any signal with the braid grounded.
Keep in mind that there are really three conductive surfaces on any piece of single-shield coaxial cable. One is the outer surface of the center conductor. The other two are the inner and outer surfaces respectively of the shield. The inner and outer surface of the shield are two separate conductors as far as high frequency RF is concerned. As long as there is sufficient shield coverage, there will be negligible leakage of the signals on the outside of the shield into the inner surface of the shield and into the receiver. Virtually none with hardline. This separation of surfaces between the inner and outer surface of coaxial cable can be compromised by poor or improper connectors, poorly installed connectors, poorly shielded receivers, poorly shielded terminations at the antenna (though this last can be improved using common-mode choking on the coaxial cable at the antenna end. > I think the > RG6 I have is cheapie stuff. It is RG6 that can be buried, but in > looking at it, the braid is not 100%. That's the first thing you'll notice about cheap coax. > There is foil, but I have no idea > how good it all is. The foil is likely not bonded to the dielectric. Take a piece apart and see if it (the foil seam) can be opened up, sort of along a folded over joint in the foil. If so, it's junk. The shield allows ingress and egress along the joint and the joint opens up even wider making things worse with handling and bending, also temperature variation. (I want to use stronger terms for the poor quality of cable manufactured like this, but can't on a family list.) There is good RG-6 available, including direct burial cable. This would have 98% tinned shield coverage, a foil shield bonded to a polyfoam dielectric, copper plated steel center conductor, as well as flooding compound between the jacket and the shield braid, all surrounded by an abrasion resistant insulating jacket. > So going to quad shield will probably solve my > problems. If I had to bet on it, I'd think so. Do keep in mind that most quad-shield coaxial cable is designed as head end cable and is not going to last long outdoors buried. You might want to keep this in mind when you look at cable types. The other thing is that quad-shield cable does not use standard connectors. You'll want to get the proper cable prep cutting tool, and need a supply of the proper crimp on connectors, along with the proper crimping tool. If you attempt to use what tools you have for your RG-6, you are wasting your time and cash on the quad-shield cable. As I described above, you *have* to have the connectors installed on the cable correctly to get the isolation you want between the inner surface of the shield and the outer surface of the shield. Without that isolation you have your current situation of strong ingress via common-mode currents, and the ingress will happen again. > should not be getting CBU at S9! Correct. 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]
