Topband: RG-6 Coaxial Cable...

Tom Rauch w8ji at
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 
> pulse-forming
> 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.

73 Tom

More information about the Topband mailing list