Re: Using HV COAX without stripping the shield

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Ed,

While googling to get specs on RG8U, I found stuff with foam.  It 
seems like it is useful in UHF applications where losses become 
siganificant.  I have about 50-70 feet of the PE version at 400+ MHz 
and I lose half of my power in the cable.  Anyway,  I believe as Jim 
says, that the inner and outer dimensions of the coax help determine 
the impedance (the inductance per foot).  The permitivity of the 
dialectric along with these dimensions determine the capacitance per 
foot.  Permitivity seems to be part of the equation for Zo so 
everything else the same, changing permitivity would affect the 
impedance it seems.

Gerry R.


> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
> "Hi Jim,
>
> OK this is good to know.  I have never seen 50 ohm coax with foam 
> nor 75 ohm coax without foam, but then again.......
>
> Gerry R."
>
>    There's lots of cheap 50 ohm "RG-8 type" coax around with foam 
> insulation and very skimpy copper outer braid.  Crummy stuff.
>
> Ed