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Which TV antenna cable is live?

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Freddyfruitba...
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PostPosted: 12:08 - 12 May 2019    Post subject: Which TV antenna cable is live? Reply with quote

I am trying to work out which, if any, of several coax cables protruding from wall and floor are connected to the TV aerial on the roof (and also which I can therefore rip out). For various reasons its not straightforward to follow the cable runs visually. Although I do have a TV it is not tuned in to any digital channels, so it's not simply a case of plugging in each cable in turn and seeing which one works.

Admittedly I could plug in and run the entire TV set-up procedure for each cable in turn (and I may end up doing that) but is there a simple way of diagnosing them with a multimeter or something? Would quite like to know for future reference.
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Easy-X
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PostPosted: 12:29 - 12 May 2019    Post subject: Reply with quote

There are meters for signal strength but they're tuned to look for specific frequency bands. I don't think a standard multimeter is going to be of much help.

Most TVs usually have some sort of signal strength meter themselves... but you have to tune it in first. Tune it, and see which lead has the most signal strength and that'll probably be the one.

Any idea what the other co-ax cables are for?
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The Shaggy D.A.
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PostPosted: 13:44 - 12 May 2019    Post subject: Reply with quote

I just had to do that with a TV amplifier in the loft with 6 outputs, but no labelling as to where they go. Simplest method was to short out the core and shield at one end, and then multimeter on resistance between the core and shield on the other - if you have continuity, you've identified the cable.
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Confusion
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PostPosted: 13:58 - 12 May 2019    Post subject: Re: Which TV antenna cable is live? Reply with quote

Freddyfruitbat wrote:
....is there a simple way of diagnosing them with a multimeter or something?.....


That depends on what is connected to the other end of the cable.
Some types of TV aerial have the co-ax cable connected to a
folded dipole or to a shorted-stub matching circuit. This will
appear as a short circuit on a DC test with a multimeter.
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Nobby the Bastard
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PostPosted: 15:12 - 12 May 2019    Post subject: Reply with quote

The Shaggy D.A. wrote:
I just had to do that with a TV amplifier in the loft with 6 outputs, but no labelling as to where they go. Simplest method was to short out the core and shield at one end, and then multimeter on resistance between the core and shield on the other - if you have continuity, you've identified the cable.


Thats exactly what I was going to do when I was diagnosing an coax issue.

Turned out that the cabl:e to the tv was bust but I checked it in basically the same way.
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Freddyfruitba...
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PostPosted: 20:22 - 12 May 2019    Post subject: Reply with quote

HardlyDavidson wrote:
Most TVs usually have some sort of signal strength meter themselves... but you have to tune it in first. Tune it, and see which lead has the most signal strength and that'll probably be the one.

Yeah, having to connect up and run the tuning-in procedure for each cable was what I was trying to avoid, but looks like that's the only option

HardlyDavidson wrote:
Any idea what the other co-ax cables are for?

Probably historical cables linking rooms; feeds for now-missing satellite dishes/cable TV; god knows.

The Shaggy D.A. wrote:
Simplest method was to short out the core and shield at one end, and then multimeter on resistance between the core and shield on the other - if you have continuity, you've identified the cable.

So, I just need to climb up the roof and shin up the chimney to reach the cable end, and Robert will be my auntie's brother! Laughing
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chris-red
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PostPosted: 12:47 - 13 May 2019    Post subject: Reply with quote

If you have both ends and a mate you can short it it and one and test the continuity with a multi meter.
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t121anf
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PostPosted: 12:52 - 13 May 2019    Post subject: Reply with quote

Is the cable even worth saving? Old coax is generally rubbish.
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weasley
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PostPosted: 13:11 - 13 May 2019    Post subject: Reply with quote

If the top end of the cable is connected to an antenna, shouldn't there be continuity? In which case just test all the cables you can see for continuity and see which, if any, show up. Worth a shot if you have a multimeter handy. If they all show up as open circuit then you are no further forward, but if one sticks out it is worth trying that one first with a TV.
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Old Thread Alert!

The last post was made 4 years, 321 days ago. Instead of replying here, would creating a new thread be more useful?
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