Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!decwrl!hayes.ims.alaska.edu!floyd From: floyd@ims.alaska.edu (Floyd Davidson) Newsgroups: comp.dcom.modems Subject: Re: Help: My telco has mid and high frequency loss Message-ID: <1991Jan9.074047.1894@ims.alaska.edu> Date: 9 Jan 91 07:40:47 GMT References: <88953@lll-winken.LLNL.GOV> Organization: University of Alaska, Institute of Marine Science Lines: 120 In article <88953@lll-winken.LLNL.GOV> casey@gauss.llnl.gov (Casey Leedom) writes: > > [...] > I've been told that the two zero drop outs are for the PEP retraining >signals. The big issue is that the mid and high frequency sub-carriers >don't seem to be up to snuff. Note that high frequency roll-off is normal for long cable runs. The real problem is signal to noise ratio, which frequency response certainly does affect. [...] >me -- this is my second great experience with PacBell service technicians >by the way) or whether they really don't have any method of doing a >frequency response test. I suppose their attitude could be that there's >really nothing simple (read "cheap") that can be done if there is a >frequency line impairment, so why bother test -- besides, it would give They might not be able to do it. But what you say may also be true, and in fact they may not be able to do anything about it. If you are that far from the switch... well you are still going to be that far from the switch, no matter which cable they use. [...] > The service technician who came out also mentioned that my house is >just about as far from the central office as I could get without being >assigned to a different CO. However, he thought that all the street [...] > The other possible source of these problems is the house wiring. The >wiring in the house is very old, untwisted aluminum 3-pair. Yes, I said >aluminum! Don't ask me -- everyone I've told of and showed the wiring to >says they've never heard of aluminum being used for telephone wiring ... >and some of them have been in the telephone business for over twenty >years! Never, ever, heard of it. Is it really untwisted too? Replace it. > While in PEP mode, I can hear a very small amount of cross talk when >both the modem and voice lines are idling (very low level regular >clicking.) As soon as the modems start up it becomes nearly impossibly >to hear the cross talk. I don't think I can hear any cross talk when >using V.32. Disregard this as a meaningful test. Any noise you can actually distinguish from the modem tones will blow the modem away. But what you are hearing could be coming from the modem, you just can't tell with your ear. (I can to some degree with some kinds of modems and I know people who are better than I am at it. But we don't trust our ears, and we have been at it for a long long time.) [...] > So, the point of this article: > > 1. I welcome any comments about frequency response testing and > getting PacBell to fix their wiring if it's the problem. > And just what are the nominal levels of service that they > do promise to provide? I'll pass on this. I don't know what PacBell sells and I'd have to dig up what a "standard" line specs are, which might be different. > 2. I welcome any comments about the potential problems that very > old, untwisted aluminum wiring might generate and in particular, > does anyone think it could be responsible for my frequency > response loss? If it really is untwisted, it sure isn't helping any. > > 3. I think I remember hearing, perhaps in this group, that twisted > pair wiring can actually *degrade* frequency response because of > capacitance coupling. Am I dreaming that up? Will I be doing > more harm than good by running copper twisted pair? It is mo' betta, by fer. (That telco cable is twisted pair all the way from the switch to you, can't be too bad.) > 4. We're thinking of running twisted copper 6-pair throughout the > house to accommodate future expansion with an Ethernet, AppleTalk > net, and up to three phone lines. Does anyone see any problem > with cross talk doing this? Depends on how you do it. A cable should be terminated with the proper load at both ends. If you run a wire from point A to point B to point C with a jack at each point there will be only one time when the cable is properly terminated: when point A and C are. If A is your demarcation box where you connect to the telco line, and B is a phone and C is a modem, then the modem going off hook is a proper load. When the phone is off hook it has this stub line going out to point C that is going to cause a problem, either on or off hook. If the line is short it isn't a problem when off hook, and just double terminates the line when on hook (reduces the volume). If the line is long it may cause things like high frequency roll-off. The important thing is it won't much bother you if B is a phone. It might if B is the modem and C is the phone. But really the best thing for modems is one line to the modem with nothing else on it. You mentioned that you are getting knocked completely off after 45-60 minutes. That is the real problem. Having a slightly slower connect speed because of a poor line is one thing, getting knocked off is another. Another problem too. It may be related to your being able to hear "crosstalk" on the lines. If in fact it is noise or crosstalk that you can hear over the modem tones, that is what is knocking you off. If it is coming from your house wiring it should relate to something local, like when the other line goes off hook, when the refigerator starts up, or something else that generates noise. Floyd -- Floyd L. Davidson floyd@ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.