# How do you test quality of a coaxial cable?

Discussion in 'Archived Threads 2001-2004' started by Andrew_Chan, Sep 24, 2001.

1. ### Andrew_Chan Agent

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How do I know what's the impedence of my coaxial cable? What is the cheapest way(include buying the equipment) to test the quality of a cable. If I make my own cable by buying parts from PE, would it be up to the 75ohm standard?

2. ### Greg_R Screenwriter

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It's not the cable that's 75ohm, it's the terminations (i.e. connectors). When you purchase your connectors, make sure that they are 75ohm.
Greg

3. ### Andrew_Chan Agent

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I thought it adds up, so if I have 75ohm connecters and my coaxial cables are 100000000 ft, the cable can still qualify to be a 75ohm impedence cable?

4. ### Steven Lin Extra

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Cable's do have impedances, and there is such a thing as 75 ohm cable, but "75 ohm" is not a resistance. That value is known as the "characteristic impedance."
How do you find the characteristic impedance of a cable? The most inexpensive way is to look it up.
Seriously, there is no inexpensive way to measure characteristic impedance. You can't use an ohmmeter. All you would measure would be the DC resistance, which is not the characteristic impedance. You can use a Time Domain Reflectometer or an oscilloscope plus a known signal source to calculate it, but neither of these qualify as cheap.
Most cables are usually labeled. If it says RG/58, it's 50 ohm. If it says RG/59 or RG/6, it's 75 ohm.
BTW, it's impossible to have a 75 ohm RCA connector. Canare claims to have one that is as close as you can get, but it still isn't truly 75 ohm. BNC connectors can be truly 75 ohm, but beware, there exist 50 ohm BNC connectors.

5. ### Andrew_Chan Agent

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So, if I make a cable with RG/58 cable + 75ohm connector, is it better than most of the cable I can buy from stores?

6. ### Steven Lin Extra

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It depends on what the cable is for. If it's video, you are better off with 75 ohm like RG/59 or, preferably, RG/6. If it's digital audio, same thing. If it's analog audio, like preamp to amp, then impedance is not that important, but you really can't go wrong with 75 ohm cable.
Apart from the quality of the cable and connectors, your skills at soldering or crimping will also determine whether or not your cable is better than what you can buy in stores. But built well, a DIY cable has a very good potential to be every bit as good, and possibly better, than what you can buy.
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Steven

7. ### Andrew_Chan Agent

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where can I find Canare connectors?

8. ### Steven Lin Extra

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Markertek has them although there are other places that are cheaper. Sorry, I don't have the other places bookmarked.
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Steven
[Edited last by Steven Lin on September 27, 2001 at 06:29 PM]

9. ### rich r Stunt Coordinator

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Where can I find Canare connectors in Canada preferably Ontario?????

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