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I'm not receiving TV in my room and the cable guy has determined that there is no signal on my coax outlet in the wall. There is a signal in other rooms, so there must be a broken or disconnected cable somewhere in the house.

Now the owner and I are going to go around the house and try to find it, but how can we measure whether there is a signal / potential on a cable without connecting a TV to it?

I've read that you need a spectrum analyzer to measure signal strength, but I don't need that, I just need to know if there's any signal at all. I've also read that you can check cables with a multimeter, but you need both ends for that, and they are impossible to bring close together in our case (the cables are in walls etc.)

(This is in the Netherlands, in case they have different standards there than e.g. the US)

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possible duplicate of Cable Signal Testers –  BMitch Jun 22 '12 at 12:41
    
@BMitch I don't need to know the actual signal strength –  Bart van Heukelom Jun 22 '12 at 12:47
3  
Well you kinda do ;) No strength = no signal. Some signal = some strength. –  The Evil Greebo Jun 22 '12 at 12:50
    
The question is a bit mis leading.. as he is not trying to test signal strength (like satleite reception or gsm signal) But just want to know how to test a coax cable. If the signal was weak the whole building would be affected not one point (except if one point has a micro short which is very rare and caused by somebody putting something heavy on the cable, or shutting it in a door, or some rats trying to eat it for lunch) –  ppumkin Jun 22 '12 at 14:49
    
The first point of troubleshooting on any coax cable is to replace the connectors, preferably with a high-quality SNS compression fitting. –  Steven Jun 22 '12 at 14:59

6 Answers 6

up vote 10 down vote accepted

You do not need to know if there is a 'signal' you just need to know if there is a connection.

A basic tool that can tell you evetrything and costs a few bucks/quid at local hardware store. Multimeter

Never in my life did i have to use a tone generator, a oscilloscope to test if my CCTV, Satellite or TV connection is giving me good enough signal.. LOL

You use that type of equipment for digital/analogue testing where you control several if not hundred outcomes, synchronization and high speed data transfer.

You just need to use a few simple free (brainpower) tricks.

Point A being nearest to your TV and Point B being the other end of the cable.

  1. Disconnect all TVs
  2. Short point B (so connect the signal and shield with a wire)
  3. Test point A with a multimeter set at Ohm

Results

  • ~0Ohm or very close to - Woohoo you have a nice connection from a to b!
  • >0Ohm More than dead short - You have a bad connection somewhere
  • No reading - Cable form Point A to Point B has no connection

There is no need to analyse the signal or test for a signal because you know you have a signal in the other TVs (assuming the coax is connected to the same place)

Alternatives

If you know the coax for all the TVs is the same cable you, you can leave Point B terminated - which is most likely closest to the antenna or after the junction. Test Point C,D...Z respectively to make sure there is a good connection.

Take your TV and connect it to a working plug to make sure the TV is not broke - or as pointed out use TV that works and plug it into your outlet - same difference I think? (but does not eliminate double jeopardy - your TV might still be knackered as well as the signal be broke :) )

Alternative 2

Also requires for all plugs to be disconnected from all TVs. Connect a 9 volt battery to one end and test all the ends for a voltage. If you get ~9 volts then the route is good. If you get a <9V then you have an issue on the route (micro short?) if you have 0V then there's no connection

Good Luck

Multimeter F.A.Q

And a photo to make it look pretty.

enter image description here

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Regarding the last sentence, we actually did the reverse, and connected the TV from another room to my outlet; it didn't receive anything. –  Bart van Heukelom Jun 22 '12 at 13:07
    
Ohh- well then the connection is bad.. simple as.. you need to find where its broken- you dont need to test signals.. :-) –  ppumkin Jun 22 '12 at 13:11
    
Yes, the cable guy already determined that :) –  Bart van Heukelom Jun 22 '12 at 13:13
    
Ok :) Soooo you gonna need to find the closest point to where the cable starts working(ie has 0ohm on a terminated cable) repalce the broken bit and join it up again.. and viola.. PS is this Digital Cable or Antenna like Freeview Digital? –  ppumkin Jun 22 '12 at 13:16

You can use a Tone Generator to find where the break in the cable is. It's still not a free option, but definitely cheaper than a signal generator. If you have a friend or relative in the phone business, those guys always have one of these in their tool belt. IT guys quite often have them too.

I'm honestly surprised that the cable guy didn't do it for you, it would have been quicker to find it for you than to explain it to you. I guess they take the premise wiring limitation pretty seriously.

enter image description here

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This is a less expensive model with good reviews. amazon.com/Sperry-ET64220-Tracker-Tracer-Master/dp/B00279JLBQ/… –  DaveNay Jun 22 '12 at 12:46

Connect a small battery to one end and try with a small lamp/tongue(dangerous) on the other end. You can easily find out which cables are working and which are not. It's the cheapest way :)

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You can use a multimeter to check the continuity to determine if the line is broken. Buy a length of wire that will reach from the outlet in the wall to the junction box with the incoming signal, i.e. 18 gauge and attach one end of the cable where it comes out of the wall (you can use electrical tape to hold it or have a helper hold it in contact with the end of the cable, not the insulation). Run the wire to to the room where the junction box is and test the continuity where the input is coming from the dish, etc. with the end of the wire. If you get a continuity signal that means the cable is good, i.e. no broken cable in the wall. If you do not get a good continuity signal then you have a broken line somewhere in the cable running to the room and you will have to take additional steps to find it.

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The first best place to check is the TV point in your room, put it out and check that it isn't loose, and not wobbly, then find the splitter box where the cable to your room is split from the main TV line, and check that the splitter box is working fine by swapping the cable from the main room to the socket for your room.

Failing that, hook a 9V battery up to the cable end in your room, then check if you get approximately 9V from your cable at the splitter box. If not then the line to your room has a break, and you need to trace the cable to find the break. If it appears that the break is in the wall, and you can easily get to the cable where it comes out of the wall in the ceiling/floor-space, and the cable seems to be able to be pulled easily, then get some strong string/fishing line, tie and tape it to the end in your room, and pull it through into the cavity where you can get to it. Go buy some new cable at approximately 50c-$1.20 a meter and pull the new cable back with the string you've pulled through the wall!. Note, caution, DO NOT BREAK/LOSE the string/line as it is much easier to get the new cable in place!

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You must look a master panel in your house and find the splitter (four way splitter possibly), for sure the line going to your room is disconnected. Now where usually the splitter is located: a closet, crawls space attic, next to the ground block. In some occasions you don't have a splitter but a house amplifier.

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