state test question about testing coax

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jsartain

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what test instrument or process do i use to test coax? do i put a voltage on it or use a digital multimeter, analog meter or capacitance tester?
 
jsartain said:
ya thats the problem i had with it too. way too vague. the question was only what do u test coax with?
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They're probably not asking you to be too technical, especially if it's multiple choice. A coax cable has a rating in ohms. RG59 is less ohms than RG6. What would you use to take these measurements in ohms?
 
mcclary's electrical said:
They're probably not asking you to be too technical, especially if it's multiple choice. A coax cable has a rating in ohms. RG59 is less ohms than RG6. What would you use to take these measurements in ohms?
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At radio frequencies a co-ax cable has a characteristic impedance. Heck, any transmission line that is geometrically consistent has a characteristic impedance. Not something that the average bear would measure. But if you had to, you might use a Time Domain Reflectometer (TDR) or maybe a Standing Wave Loss Factor (SWLF) meter. (somehow SWLF doesn't sound right - it's been a long time)
 
The impedance is 50 or 75 ohms but that is not something that can be easily measured.
A good basic test for coax is center to shield with an ohmmeter to see if its shorted, I suspect that is what they are looking for.
I test coax with a wattmeter, its used with a radio to check the forward power and reverse power. If the reverse power is too high, too much of the transmitter power is being reflected back into the radio and will damage it. A bad or poorly made connector will cause high reflected power. But an ohmmeter will find this. Low reflected power means the system is efficient.
 
i would use a multi meter to check ohms. If not open or shorted it likely will be ok. That question could be challenged. It lacks what they want you to check it for. a digital or analog can both measure ohms.
 
tom baker said:
The impedance is 50 or 75 ohms but that is not something that can be easily measured.
A good basic test for coax is center to shield with an ohmmeter to see if its shorted, I suspect that is what they are looking for.
I test coax with a wattmeter, its used with a radio to check the forward power and reverse power. If the reverse power is too high, too much of the transmitter power is being reflected back into the radio and will damage it. A bad or poorly made connector will cause high reflected power. But an ohmmeter will find this. Low reflected power means the system is efficient.
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Bold added for emphasis.

Low reflected power does not directly relate to system efficiency. Have you ever heard of a dummy load? No reflected power there at all.

Some antenna systems are most efficient operating at a high SWR.

Again, without knowing what is being tested for, it is impossible to suggest the proper tool. An antenna analyzer is a great tool if one knows how to use it and it can be used to test certain characteristics of coax. If you don't know how to use it, it is nothing more than a fancy SWR meter.
 
nakulak said:
that would depend on the voltage :grin:
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Even at extremely high voltages it would show an open a few seconds after the resultant fire....
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I'll bet I could push 50 KV through RG-8 without an arc over if it were terminated properly. The dielectric on good RG-8 is like automotive spark plug wire insulation. It's made of PTFE about the same thickness as spark plug wire insulation.
 
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