Most of you who have followed this column or have heard me speak may remember my saying, "I don`t know everything about telecommunications, but I do have a good list of contacts who do or know where to send me to look."
My research has taught me a lot over the years. My latest lesson: Do not ask a broadcast engineer about the viability of existing in-home cable-TV cabling for use with a digital satellite system. I received a lot of comments on my response to Richard Arbach in the July 1999 issue (see "Cable service and wiring," page 12).
The following letters do a much better job at addressing Mr. Arbach`s problem than I did.
David Casemore, president of Casemore Electric (Royal Oak, MI), wrote:
"Donna Ballast`s response to Richard Arbach failed to answer his question regarding the cable wiring in his house. While she brings up a valid point regarding the FCC [Federal Communications Commission], his main question--Will it work?--was not adequately addressed.
"Digital satellite systems need a higher grade of coaxial cable than does cable TV. Mr. Arbach should use RG6 Quad wire that has been sweep-tested for at least 1 gigahertz. Furthermore, if his existing system has any splitters hidden in the attic or walls that he doesn`t know about, it`s safe to assume that the satellite signal won`t even get through. The splitters used for standard cable TV just won`t cut it. Also, if he wants to replace the four cable boxes with four satellite receivers, he will need two satellite dishes.
"If the cable installed in his house will not support the satellite signal, his other option would be to run RG6 Quad wire from the dish and into a satellite receiver located in a basement or closet near the entrance point of the cable-TV cable coming into the house. He could then modulate the signal and send it up to the television sets using the old cable wiring. Most satellite receivers are equipped with an RF [radio-frequency] remote so you can change channels without being in the same room. The drawback of this arrangement is that you can`t take advantage of the S-Video outputs for best picture or the optical digital output needed for AC-3 [Dolby Digital] sound. These are the features that make satellite TV so attractive in the first place."
Ed Nielsen, with Cache Valley Electric (Salt Lake City, UT), wrote:
"While the cable-TV company legally has the right to remove all of the cable at a subscriber`s premises (with the exception, as you said, of any cable installed by the homeowner), the odds of any cable actually being removed due to a canceled subscription are less than 5%. The cable-TV company is already spending upward of $50 just to roll a truck to disconnect the service. They`re not going to spend more money to do the research to determine who the actual owner of the coax is and then have the installer remove any coax that is not homeowner-owned. They could be looking at an additional $30 on top of the truck roll. They are already losing part of their subscriber base, and the last thing they would want to do is create bitterness by leaving a bunch of holes in somebody`s home.
"Just as important as the cable itself is the manner in which it was installed. Odds are that if it was installed by the cable-TV company, it was installed correctly, using the home-run method. As you know, with the home run-method a cable is run from each outlet to a central location, where the input cable is split in this homeowner`s case by a four-way splitter. Here is where we run into problems. If the splitter was installed by the cable-TV company 10 years ago, the bandwidth of the splitter is most likely 5 to 300 megahertz. If it has been replaced within the past few years, it could be 5 to 600 MHz, or even 5 to 1000 MHz non-power passing. A satellite transmits at 950 to 1450 MHz. The low-noise block down converter (LNB) at the dish--the part that actually picks up the signals--is powered by the receiver, so the splitter must be power passing. However, these splitters pass power only on one leg (to the input). If this type of splitter were used for multiple receivers, only one receiver would control the LNB. LNBs are polarized (horizontal or vertical) as are the channels (they do this so they can get more channels in a smaller bandwidth without having to worry about co-channel interference). Consequently, whatever polarity (odd or even channel number) the controlling receiver is on, any other receivers would be limited to the same polarity (odd or even channel number).
"For two receivers, dual LNBs are used, with each receiver having its own cable. For more than two receivers, a dual LNB is still used, but a multiswitch is installed at the central location where all the individual outlets come to. The multiswitch actually powers the LNBs (one horizontal and one vertical), and the changing channels on the receiver just switch that receiver from one LNB to the other."
Many thanks to all of you who took the time to send comments. You are now on my contact list!
Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, the University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: firstname.lastname@example.org.