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Detecting where a coax cable goes to
I have what I think is an unsual question which I couldn't find an
answer to: in my attic there is a coax splitter with several coax outputs to coax cables which snake into the ceiling and disappear in the boweles of the house. They are all of the same color and have no identifying marks. In the house itself, there are coax jacks in several rooms. And now the question: is there a way to determine, without buying expensive equipment, which cable in the attic leads to which room? Since not all coax jacks in the rooms are connected to a tv, it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal. |
Detecting where a coax cable goes to
"Since not all coax jacks in the rooms are connected to a tv,
it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal" I can think of two ways right away. The way I would do it is to get a small TV and conenct it to a cable outlet. Turn the sound up high. Go in the attic and perhaps with a helper listening disconnect one coax at a time. bingo. the hard way would be to use a volt-ohm meter. disconnect all the coax in the attic and jumper one outlet across itself. then check in the attic for the line with 0 resistance. ....thehick |
Detecting where a coax cable goes to
And now the question: is there a way to determine, without buying expensive equipment, which cable in the attic leads to which room? Since not all coax jacks in the rooms are connected to a tv, it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal. Cut a small cable in two.. On one cut end wire up a 9v battery connector. On the other cut end wire up a buzzer, or at least strip it so you can use a meter to test the wire and shield. Hook the 9v at the wall outlet. Go up to the splitter and check each lead that comes up to the splitter. When you buzz, or get a 9v reading, you've found that room. |
Detecting where a coax cable goes to
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Detecting where a coax cable goes to
also: cable tv company here will upgrade your splitters and replace the
cable ends from the pole to your jacks to deliver a nice picture to your cable tv's. and: maybe time to break down and buy a digital multimeter for $25. look what you can fix with it at: http://www.repairfaq.org/REPAIR/F_ts...tml#TSHOOT_014 |
Detecting where a coax cable goes to
Sorry for the newbie question, but what happens if there is a splitter?
Also, is possible to tell - and if so, how - if there are one or more splitters between the attic and the room? And, another also, will the presense of one or more splitters affect the other approach suggested by others on this thread (volt-ohm/multi meter)? At least thehick's other idea - using a portable tv - should still work... |
Detecting where a coax cable goes to
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Detecting where a coax cable goes to
"Noozer" wrote in message news:cJzAf.300933$2k.177325@pd7tw1no... : : And now the question: is there a way to determine, without buying : expensive equipment, which cable in the attic leads to which room? : Since not all coax jacks in the rooms are connected to a tv, it's not : just a matter of disconnecting one cable after another from the : splitter and seeing which tv loses its signal. : : Cut a small cable in two.. On one cut end wire up a 9v battery connector. On : the other cut end wire up a buzzer, or at least strip it so you can use a : meter to test the wire and shield. : : Hook the 9v at the wall outlet. Go up to the splitter and check each lead : that comes up to the splitter. When you buzz, or get a 9v reading, you've : found that room. : : Good grieg, Charlie Brown! That's the hard way, and destructive, too. Read the previous post - much easier and cleaner and more dependaghle and a lot less destructvie. |
Detecting where a coax cable goes to
CJT wrote:
wrote: Sorry for the newbie question, but what happens if there is a splitter? Also, is possible to tell - and if so, how - if there are one or more splitters between the attic and the room? And, another also, will the presense of one or more splitters affect the other approach suggested by others on this thread (volt-ohm/multi meter)? At least thehick's other idea - using a portable tv - should still work... If there's another splitter, then it depends on the particular splitter in question -- some will pass DC, others won't. If it doesn't pass DC, then neither the buzzer nor the meter will register the battery's voltage. As for using a TV, it'll introduce some ambiguity there, too, since you might have two (or more) equally good signals. If you have the same number of wires in the attic as wall connections, there's probably not another splitter. If there were more splitters, it would be unlikely that they would be hidden away somewhere. Splitters and connectors do occasionally fail and they would have to be accessible for service. Depends on the intelligence of the installer. Bob |
Detecting where a coax cable goes to
If the cable was daisy chained as was the custom years ago, there could
be a splitter at every outlet. My last house had a run with 9 splitters in it. Needless to say, it didn't do very well with a broadband connection! From:RobertM CJT wrote: wrote: Sorry for the newbie question, but what happens if there is a splitter? Also, is possible to tell - and if so, how - if there are one or more splitters between the attic and the room? And, another also, will the presense of one or more splitters affect the other approach suggested by others on this thread (volt-ohm/multi meter)? At least thehick's other idea - using a portable tv - should still work... If there's another splitter, then it depends on the particular splitter in question -- some will pass DC, others won't. If it doesn't pass DC, then neither the buzzer nor the meter will register the battery's voltage. As for using a TV, it'll introduce some ambiguity there, too, since you might have two (or more) equally good signals. If you have the same number of wires in the attic as wall connections, there's probably not another splitter. If there were more splitters, it would be unlikely that they would be hidden away somewhere. Splitters and connectors do occasionally fail and they would have to be accessible for service. Depends on the intelligence of the installer. Bob |
Detecting where a coax cable goes to
wrote in message ups.com... I have what I think is an unsual question which I couldn't find an answer to: in my attic there is a coax splitter with several coax outputs to coax cables which snake into the ceiling and disappear in the boweles of the house. They are all of the same color and have no identifying marks. In the house itself, there are coax jacks in several rooms. And now the question: is there a way to determine, without buying expensive equipment, which cable in the attic leads to which room? Since not all coax jacks in the rooms are connected to a tv, it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal. Let's assume there are no other splitters involved. Forget the battery method. Go to RadioShack or equivalent and buy a 75 ohm terminator. If you don't own a test meter, get the cheapest one you can find that measures resistance. Disconnect all the sets that are attached to the cable system Put the terminator on one wall outlet. At the splitter disconnect, all the cables. Take the meter and at the splitter end find the cable that measures about 75 ohms between the center pin of the cable connector and the outside of the cable connector. Tag both ends of that cable. Move the terminator to the next wall outlet and repeat. Having an assistant who can move the terminator around and communicate to the attic is a great time and effort saver. Charlie |
Detecting where a coax cable goes to
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Detecting where a coax cable goes to
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Detecting where a coax cable goes to
wrote in message ups.com... I have what I think is an unsual question which I couldn't find an answer to: in my attic there is a coax splitter with several coax outputs to coax cables which snake into the ceiling and disappear in the boweles of the house. They are all of the same color and have no identifying marks. In the house itself, there are coax jacks in several rooms. And now the question: is there a way to determine, without buying expensive equipment, which cable in the attic leads to which room? Since not all coax jacks in the rooms are connected to a tv, it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal. Other posters have given you reasonable suggestions for identifying the cables. But I'm wondering why it matters as long as each outlet is feeding the same signal from the same source -- the splitter. A caveat -- In a setup such as yours, each unused outlet should have a 75 ohm terminator. Radio Shack has them. Unterminated cables can mess up the signal to the active devices on the network. SJF |
Detecting where a coax cable goes to
"SJF" wrote in message news:aDEAf.9492$bF.1572@dukeread07... wrote in message ups.com... I have what I think is an unsual question which I couldn't find an answer to: in my attic there is a coax splitter with several coax outputs to coax cables which snake into the ceiling and disappear in the boweles of the house. They are all of the same color and have no identifying marks. In the house itself, there are coax jacks in several rooms. And now the question: is there a way to determine, without buying expensive equipment, which cable in the attic leads to which room? Since not all coax jacks in the rooms are connected to a tv, it's not just a matter of disconnecting one cable after another from the splitter and seeing which tv loses its signal. Other posters have given you reasonable suggestions for identifying the cables. But I'm wondering why it matters as long as each outlet is feeding the same signal from the same source -- the splitter. A caveat -- In a setup such as yours, each unused outlet should have a 75 ohm terminator. Radio Shack has them. Unterminated cables can mess up the signal to the active devices on the network. SJF That goes for any unused connections on the spliter(s) as well. |
Detecting where a coax cable goes to
"Other posters have given you reasonable suggestions for identifying
the cables. But I'm wondering why it matters as long as each outlet is feeding the same signal from the same source -- the splitter. " Interesting you should ask (and, btw, you seem to be the first to do so...). Anyway, a little off topic, but the reason for the question is this: the cable company's feed starts from the attic and is being split into various rooms as I described. What I would like to do is intall in the attic an HTDV over-the-air antenna and feed the signal from that to an HDTV in one of the rooms. I don't want to run a new cable from the attic thru the second floor to the first floor (where the HDTV is located); I just don't have the skills (and probably tools) required for that kind of job. So, in my infinite wisdom, I figured that if I can determine which cable goes to the room in question, I'll just disconnect it from the splitter and connect it to the OTA HDTV antenna in the attic (using a coax coupler) and to the HDTV in the room and voila! OTA HDTV reception. I understand that by doing that I give up regular cable reception in that room but (1) it's a problem for another day and (2) it's not really much of a problem anyway since I don't intend to user that for the usual cable fare. So that's the reason.... |
Detecting where a coax cable goes to
Well, that's a departure from the other proposals :) Just to be on the
safe side, I'm going to get tomorrow both a buzzer and a 75 ohm terminator! I already have a 9v battery and even a multimeter - analog, unfortunately, but it does measure resistance, so I should be all set (assuming by wife agrees to act as the assistant...) As an aside, I must say it NEVER occured to me how useful a multimeter is. Talk about learning something new every day. |
Detecting where a coax cable goes to
" A caveat --
In a setup such as yours, each unused outlet should have a 75 ohm terminator. Radio Shack has them. Unterminated cables can mess up the signal to the active devices on the network. SJF That goes for any unused connections on the spliter(s) as well. " Wow, for someone who is regulary considered by his friends as a more or less maven, I now feel unbelievably ignorant ): I guess ignorance is relative... I have never heard of 75 ohm terminators, nor of the problems caused by unterminated cables and unused connections on splitters. As I mentioned in another response - learn something new every day. |
Detecting where a coax cable goes to
The center conductor of the coax is acts a small broadcast antenna (as
well as a receiver) the outer shield serves to contain the signal on the center conductor to prevent both radiated signal leakage and reception of over-the-air signals. The exposed end of the cable or splitter connection is breaks the "seal" on the system and allows for leakage and reception of unwanted signals. The terminator acts like a lid on jar and maintains the cables impedance. " A caveat -- In a setup such as yours, each unused outlet should have a 75 ohm terminator. Radio Shack has them. Unterminated cables can mess up the signal to the active devices on the network. SJF That goes for any unused connections on the spliter(s) as well. " Wow, for someone who is regulary considered by his friends as a more or less maven, I now feel unbelievably ignorant ): I guess ignorance is relative... I have never heard of 75 ohm terminators, nor of the problems caused by unterminated cables and unused connections on splitters. As I mentioned in another response - learn something new every day. |
Detecting where a coax cable goes to
Good guess.
Wrong reason. The unterminated piece of cable, either open or shorted, creates a phenomenon called a standing wave. Depending on the length of the offending cable and whether it is opened or shorted, the wave can raise the dickens with the right signals. Terminating the cable in the correct impedance doesn't let the standing wave be created. Take a look at http://www.glenbrook.k12.il.us/GBSSC...es/u10l4b.html It talks about standing waves in a string, but the concept is similar for liquids and radio waves. Charlie "BruceR" wrote in message ... The center conductor of the coax is acts a small broadcast antenna (as well as a receiver) the outer shield serves to contain the signal on the center conductor to prevent both radiated signal leakage and reception of over-the-air signals. The exposed end of the cable or splitter connection is breaks the "seal" on the system and allows for leakage and reception of unwanted signals. The terminator acts like a lid on jar and maintains the cables impedance. " A caveat -- In a setup such as yours, each unused outlet should have a 75 ohm terminator. Radio Shack has them. Unterminated cables can mess up the signal to the active devices on the network. SJF That goes for any unused connections on the spliter(s) as well. " Wow, for someone who is regulary considered by his friends as a more or less maven, I now feel unbelievably ignorant ): I guess ignorance is relative... I have never heard of 75 ohm terminators, nor of the problems caused by unterminated cables and unused connections on splitters. As I mentioned in another response - learn something new every day. |
Detecting where a coax cable goes to
wrote in message oups.com... "Other posters have given you reasonable suggestions for identifying the cables. But I'm wondering why it matters as long as each outlet is feeding the same signal from the same source -- the splitter. " Interesting you should ask (and, btw, you seem to be the first to do so...). Anyway, a little off topic, but the reason for the question is this: the cable company's feed starts from the attic and is being split into various rooms as I described. What I would like to do is intall in the attic an HTDV over-the-air antenna and feed the signal from that to an HDTV in one of the rooms. I don't want to run a new cable from the attic thru the second floor to the first floor (where the HDTV is located); I just don't have the skills (and probably tools) required for that kind of job. So, in my infinite wisdom, I figured that if I can determine which cable goes to the room in question, I'll just disconnect it from the splitter and connect it to the OTA HDTV antenna in the attic (using a coax coupler) and to the HDTV in the room and voila! OTA HDTV reception. I understand that by doing that I give up regular cable reception in that room but (1) it's a problem for another day and (2) it's not really much of a problem anyway since I don't intend to user that for the usual cable fare. So that's the reason.... Logical reason -- and a good work-around. SJF |
Detecting where a coax cable goes to
Mmmmm!
Any unterminated cable looks like reactance to the rest of the circuit. How much effect it has mainly depends on whats between it and the other sections. A splitter like what one finds in motels with long runs has only a small signal going to the TV and most of it continuing to the next splitter. There is minimal effect leaving this configuration unterminated. If however you are splitting the power in half (like most home splitters) the effect will be greater. Worst case it could look like a short circuit on one output port of the splitter, thus lowering the other o/p port somewhat. You can also increase line losses by the increased line VSWR but this is a very small figure next to the coax resistive losses. The simple rule is if you think you have a problem, try terminating and check the effect on all TV channels. If you dont want to buy a terminator just add an extra bit of coax (to the unterminated one) for a test. If you have a strong signal in your area you may not need worry. The biggest problems I have seen with CATV systems is the lack of good connector earth connections yielding bleedthrough and low s/n performance. Coax will only radiate or receive signal direct into the jacket if there is a current inbalance inner to outer conductor. This generally mean an asymmetric source or load. An open, shorted or high line VSWR doesnt cause this problem. An effective "short" or "open" situation only exists where the length of the unterminated cable is either odd multiple of a 1/4 wavelength (short) or multiples of a half wavelength (open) for ONLY the frequency of interest. If the frequency doubles the wavelength halves. That gets very complex with so many different TV freqs. This is in fact a very good way of making a filter. If you were for example watching TV from both a very weak and very strong station and needed a masthead preamp for the weak one, chances are the strong signal will break through. If you attach a piece of coax cut to a 1/4 wavelength of the strong station at the preamp input it will null it by maybe 20-30dB. Note that the other end of the coax needs to be waterproofed and the length modified (shorter) by the velocity factor of the coax (between 0.66 and 0.82 or so. Foam RG6 would be about 0.82) Apologies for the waffle. I couldnt resist! Cheers Bob Charlie Bress wrote: Good guess. Wrong reason. The unterminated piece of cable, either open or shorted, creates a phenomenon called a standing wave. Depending on the length of the offending cable and whether it is opened or shorted, the wave can raise the dickens with the right signals. Terminating the cable in the correct impedance doesn't let the standing wave be created. |
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