VHF coax resistance question

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william3045

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Jun 17, 2004
132
- - pueblo, co
i just pulled 30' of rg8 mini up my mast and installed new pl-259 connectors. i put a meter on it before finishing-up and connecting to my new antenna and measured aprox 2.5M ohm center to shield. (coax disconnected at both ends). this is too high for having actually having shorted even a single strand but i expected a dead open. if i leave the meter connected the R keeps increasing. anyone have an idea why i am not reading infinate R before i tear it apart and do it again? tia~ william
 
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Don

open circuit reasistance

the reading is a function of the meter circuitry as well as the line - what you should be seeing is the same open reading as you would if you touched nothing with the probes. If other than that, you have a braid short likely at the connector(s). You might also have a bad PL259 so check those too. Don
 
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patrick

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Jun 7, 2004
944
Birch Bay Washington
You are reading capacitance charging

not resistance. If you have a very high impedance meter which you probably do, this is normal. Try leaving the probes on for about ten seconds. That charges the "capacitor". Then quickly reverse the connections. It will show a low resistance for a brief time (while the previously applied voltage is discharged through the meter) and then will continue to increase and ultimately read as before. You might also have some moisture in the cable which will read some constant finite resistance. Try measuring the resistance between your fingers and see what you get. Then lick them and try again. The main thing that you are concerned with as to the coax is that it is not a low resistance from the center conductor to the shield and that the continuity is good from one end to the other for both circuits. I would not advise tearing anything apart given what you have said.
 
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william3045

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Jun 17, 2004
132
- - pueblo, co
i'm definetly seeing capacitance

charge and discharge....but why. only thing i can think of is some moisture. 2.5M is definetly not a hot short. even a single strand of shield would read short at a connector...or at least a very low R...but the only dielectric i can think of would be moisture. if i ground center to mast at one end with a piece of wire and 2 clips and go to the other end and read center to mast i have continuity. same for shield to mast so continuity is good. i'm also careful not to be touching the probes so its not reading through me. guess i'll leave it "bake-out" for a few days and see how it reads. thanks guys~ william
 
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