Which is it, RG59 or RG6?
in [Repair]
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From: Michael A. Terrell on 6 Dec 2009 22:46 Joe Rooney wrote: > > Keep in mind a 3 way splitter has two 3.5db and one 7 db out. Not all of them. If you know where to look, you can find three way splitters with -5 dB at each port. They were in use in CATV in the early -80s. I kept a small stock of them at the United Video system in Delhi Township (Cincinatti, Ohio) for installs where the standard version wouldn't work. -- Offworld checks no longer accepted!
From: Michael A. Terrell on 6 Dec 2009 22:51 Jeff Liebermann wrote: > > On Sun, 06 Dec 2009 12:03:52 -0500, mm <NOPSAMmm2005(a)bigfoot.com> > wrote: > > >On Sun, 6 Dec 2009 00:24:47 -0800, "Joe Rooney" > ><ikerooneyat(a)bigvalley.net> wrote: > > >>Keep in mind a 3 way splitter has two 3.5db and one 7 db out. > > Wrong. A splitter reduces the output by -3dB which is half the power. > The extra -0.5dB loss is from losses in the bifilar wound xformer. If > two of the ports each have half the input power, there's nothing in > the budget left for the 3rd port. Part of the extra .5 dB loss is in the cast aluminum 'F' connectors. I ran Q. A. I ran tests on hundreds of samples to qualify them for our MSO to purchase the best quality we could find. We bought splitters by the thousands, and coax by the pallet Also, eight way splitters are listed at -10 dB, not 10.5. -- Offworld checks no longer accepted!
From: Michael A. Terrell on 6 Dec 2009 22:57 mm wrote: > > On Sun, 06 Dec 2009 09:17:54 -0800, Jeff Liebermann <jeffl(a)cruzio.com> > wrote: > > >On Sun, 06 Dec 2009 12:03:52 -0500, mm <NOPSAMmm2005(a)bigfoot.com> > >wrote: > > > >>On Sun, 6 Dec 2009 00:24:47 -0800, "Joe Rooney" > >><ikerooneyat(a)bigvalley.net> wrote: > > > >>>Keep in mind a 3 way splitter has two 3.5db and one 7 db out. > > > >Wrong. A splitter reduces the output by -3dB which is half the power. > >The extra -0.5dB loss is from losses in the bifilar wound xformer. If > >two of the ports each have half the input power, there's nothing in > >the budget left for the 3rd port. > > > >Googling for a typical 3 way splitter: > ><http://www.twacomm.com/catalog/model_CT413.htm?sid=1F79205DEA0D1B9FF1BF82ACDC4C33D2> > > It says "3 way-loss 2 at 6.5 DB, 1 at 3.5 DB, 20 DB isolation DC > passive" > > What does DC passive mean? Will it transmit DC power to an amplified > antenna, for example? Yes. Some splitters will pass DC, usually only to one port. The 20 dB isolation means that the return loss is more than 20 dB. This is to prevent the local oscillator from one TV causing interference to another TV. I was the engineer at a CATV system with over 10,000 active drops. There are hundreds of myths and half truths about the hardware used for CATV systems. > >I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes > >more sense. (Actually, it should be -7.0dB loss). An ideal splitter would be 3 dB, 6 db, 9 db etc., but connector losses, and to a smaller extent, core losses in the broadband transformers add the fractional losses. > >A 3 port looks like a tree. It starts with a two port splitter, where > >one output is brought out for -3.5dB loss. The other port goes to yet > >another splitter, with again divides the output in half, for -7dB from > >each of the two ports. > > >>Aha. That would certainly account for a difference! I'll check > >>later today. In fact, I'll take out the splitter and connect just > >>the one giving me trouble. > > > >Except that you said you're using 2 and 4 way splitters, which are far > >more common than a 3 way. > > I did have a 4-way in there, but later on the slim possibility > something was wrong with the splitter, I switched and the next one I > found in my drawer was 3-way. Of course the problem pre-dates the > 3-way, but I jumped to the conclusion that the 4 way might have had > something like this too. > > I realize now I shouldn't have used a 4 way since i never had plans to > use more than 3 of them, but 25 years ago, I iddn't know they made > 3-ways. > > Thanks. -- Offworld checks no longer accepted!
From: Michael A. Terrell on 6 Dec 2009 23:04 mm wrote: > > On Sat, 5 Dec 2009 20:12:17 -0800 (PST), "hr(bob) hofmann(a)att.net" > <hrhofmann(a)att.net> wrote: > > > > >Try connecting each set directly by replacing the splitters with thru > >connectors and see if they all work ok. This will require that you > >undo and redo a bunch of connections as you check out eachset and > >associated cables,, but it is the only way to be sure that your basic > >components are good. I agree with other posters that bad crimp > >connectios are a frequent problem. A little corrosion aftrer 25 years > >may make the contact between the outer shield/aluminum ground wire to > >the connector outer housing intermittent and that can do wonderous > >things. If the output of the dvr is of typical levels, it should > >easily drive another set 30 feet away. I have a 3-way splitter on the > >output of my cable box and it drives the nearby tv as well as two > >other sets 30 feet away, using a 1-3 splitter, with perfect pictures. > > When I first got cable tv -- I don't have it anymore --, the guy ran > the cable in through the floor of the close, which overhangs the first > floor. The cable box connected to a channel control dial via a cable, > no infra-red, and I told him I wanted to keep the box in the closet, > out of my way. > > He said he wasnt' sure if the tv could that far from the box. The tv > was about 6 feet away. > > Later when I connected the first remote tv and was running the co-ax > through the basement ceiling, so for some reason it was 3 times as > long as it would be when I was done, it was about 120 feet and it > still worked fine, but he thought 6 might be too much. (I didnt' get > the slightest impression he was looking for a tip for him to make a > wire 7 feet long, but maybe I'm dense and that's what he wanted?? > That didn't occur to me until just now.) Cable installers are first tier techs. They aren't trained to think, or troubleshoot. The standard cable between the TV and the converter was three feet, because that worked with 99% of the TVs in use. You should see the calculations needed to design a trunkline or feeder, or even worse, to interconnect two CATV systems. I wrote software in the mid '80s to allow me to select the hardline by size and vendor, along with the passives. Our designs called for a minimum of +10 dB at the tap, but to minimize the number of trunk or bridger amplifiers. You used a strand map to get accurate distances to calculate the cable losses, then selected the tap required. That added a block of loss to the feeder. Each calculation was based on the ones before it. -- Offworld checks no longer accepted!
From: Michael A. Terrell on 6 Dec 2009 23:11
Jeff Liebermann wrote: > > On Sat, 5 Dec 2009 20:30:48 -0800 (PST), Robert Macy > <macy(a)california.com> wrote: > > >Sorry, for jumping in here in the way of Jeff's capable hands, > > Grumble... > > >but > >agree with honing in on potential bad connections in that old coax. > > There's a fairly easy way to detect bad connections. These invariably > result in coax leakage, where the coax cable magically becomes an > antenna. Find a portable TV receiver, tune it to CATV channels not > OTA (over the air) channels, and sniff around with the portable > antenna looking for leaks (actually called "ingress"). This is > roughly what the CATV people do along the distribution cables using a > pilot carrier. A broken shield, broken connector, and possbibly a > missing termination, should all show up as excessive leakage. Ingression is external signals getting into the CATV plant. You are describing radiation' where the signal is lost to being radiated from the outer conductor, due to poor connections. It is monitored on a continuous basis on most cable systems using 'Sniffer' or other brands of monitoring equipment. While the signal is on the video carrier frequency, it is FM modulated with annoying audio to make it easy to identify. > Personally, I prefer visual inspection, a TDR (time domain > reflectometer), signal level measurements, or just a pre-emptive > replacement. Those are OK if you can shut a system down for repairs. Poor connections in the trunkline can be detected by reading the voltage drop between the coax and the amplifier housing, splice block or any other splice in any powered cable. 60 volts modified sine wave AC @ 30 amps from a CVT doesn't tolerate much resistance without causing hum modulation or burning up a connector. -- Offworld checks no longer accepted! |