Topband: RG-6 Coaxial Cable...
w8ji at contesting.com
Thu Sep 14 14:03:26 EDT 2006
> Is there any reason to think that RG-11 would behave
> differently than RG-6?
No, other than it actually tests higher in breakdown
> I have a 300 ft. length of it that I've ruined, using it
> in a pulse
> generator. It was used to store about 10 kV as part of a
> network. It broke down after a few tries and now isn't
> much good over a few
> hundred volts.
The problem with pushing energy into the cable and/or
pulling it out rapidly in a pulse application is similar to
problems that occur when using electrically long coaxial
capacitors... there are standing waves in the line.
We can apply 10kV at one end but that doesn't mean the peak
voltage along the line is limited to 10kV. When the
frequency is high enough compared to line length or if the
charge and discharge time period is fast enough there can be
substantial standing wave voltages.
Conventional transmission line modes are different.
There are interesting toys we can build. If we charge a long
transmission line to a high voltage (but well within
breakdown limits) and instantly short one end, the other end
can be made to arc over a surprising distance! Sometimes we
can make the voltage peak occur someplace in the middle of
the line and punch through the dielectric there. That isn't
because it fails at x kV, it's because the sudden level
transition at one end makes standing waves that generate
many times x kV elsewhere on the line.
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