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I'm trying to join two ends of co-axial cables. I've managed to connect the two ends of copper wires but still the signal response is very low. When I try to stretch the cable signal gets good. Why does this occur? Is there a reason some sort of special procedure is needed to join the two ends of co-axial cables?

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Make sure the inner core is not in contact with the outer wire mesh. Blunt any pointy mesh ends. Those things act as antennas and pick up ambient RF. –  Antillar Maximus Dec 24 '11 at 14:22
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Ordinarily I would insta-close this as off topic, but I suppose it doesn't hurt to expand the scope of the site a bit to encompass less abstract questions. –  David Z Dec 24 '11 at 16:15
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@David you've too much Christmas goodwill because this has no physics content whatsoever and should be migrated to electronics stack exchange ;) –  Physiks lover Dec 24 '11 at 21:01
    
@Physikslover I doubt that it would be appropriate for Electrical Engineering - that's about circuit construction, but this is a hardware question as originally asked. Maybe it would fit on Home Improvement. But the reason I left it open is that if you get into the reasons behind it, as the existing answers do, there is some physics involved there. I edited the question to clarify that, which hopefully helps it look more appropriate for the site. But of course if the community at large disagrees that this is on topic, I can close or migrate it. –  David Z Dec 25 '11 at 2:55
    
The effects in coaxes are physics, there is reflection and interference of signals, and electronics of this sort is a major component of experiments. It is ridiculous to think this should be closed. +1. –  Ron Maimon Dec 25 '11 at 4:47
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2 Answers 2

up vote 3 down vote accepted

I suppose the figure in this link is what you are talking about.

The reason one uses a coaxial cable is in order to reduce unwanted interference with the signal.

One advantage of coax over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors.

So it is not enough to just join the two copper leads ( shown in figure) because the isolation of the signal between the two copper surfaces ( inner wire and outer mesh) is lost at the break.

How to improve: Make sure that the solderings are good and large enough, not small point contacts. Wrap plastic electrician's insulating tape around the inner wire region to mimic the thickness of the internal plastic. Use aluminum wrap for the exposed length to mimic the mesh, if you put a bit of solder with the mesh,better. Wrap the whole in insulating tape. That should do it.

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I see. I went to the shop and asked for it. They gave me something called co-axial cable coupler or connectors (i'm not sure) I just inserted the two ends of copper wires at both ends and the signal is fine now. –  user1032431 Dec 24 '11 at 15:30
    
Well, yes. I thought you wanted a DIY. –  anna v Dec 24 '11 at 16:18
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The best way is to use specialized connectors available in market. They will reduce your EM interference considerably than any DIY approach.

You will need a wire cap for both end and a connector to join the wire cap.

But if you are not looking for any professional solutions, @anna 's answer might be good enough.

You can get a very technical description of what that mean here

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