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Re: Using HV COAX without stripping the shield

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 10:50 AM 11/4/2005, Tesla list wrote: 
Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Mike,

I'm not necessarily taking issue with Dr R. I'm suggesting an alternative way to fix the problem. Getting rid of the coax shielding doesn't get rid of the transmission line, but it certainly does change it and this may be enough to "fix the problem".

BTW, RG8 is 50 ohm cable and the dialectric is PE not foam. 75 ohm cable typically uses foam to get the higher Zo.

50 and 75 is independent of foam (in that, you can get solid or foam dielectric for either). The foam is used for lighter weight and lower loss at high frequencies (e.g. for Cable TV at hundreds of MHz, dielectric loss is important). Solid has a higher breakdown voltage. Foam has a higher propagation velocity (because epsilon is lower).

Impedance (Z0) is a function of the ratio of inner and outer conductor diameters (and dielectric constant).