Re: Using HV COAX without stripping the shield

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Mike" <induction@xxxxxxxxxxx>

Hi Gerry,
                The DR. is right, if you want to stop the voltage 
gain in the coax, to stop the Blumlein effect, remove the shield.
Likely you are using RG8 because the inside conductor is jacketed in 
fairly good/heavy plastic or these days, foam.
You cut away the shield, you've removed the ~ 29 pf per foot (forgot 
the value but think that's it) and without the coaxial C you loose 
the ring back power gain.
Google and check out Blumlein power supplies, nice way to 2 X or 4 X 
or more, your pulse power. Used in some big pulse systems. 
Termination Z is important on the line for full effect, also it is 
possible to get reversal of polarity on a DC pumped system and you 
can design that in or out.
Some systems have used a larger counterpoise around most of the 
center line sides but not 360 degrees, I think U of Texas HV lab did 
a lot of work in this area.
Very fast lines, though, if your looking for high current and voltage 
gain. The networks you spoke about would need to take the ~ 300 amp 
at 2 X voltage and sink it.
Cure sounds worse than the problem. Skin the coax else use it as a 
power supply component.
Mike

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, November 03, 2005 10:40 AM
Subject: Using HV COAX without stripping the shield


> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi All,
>
> It has been mentioned in the group in the past that there can be a 
> high frequency resonance when using a coax cable such as RG8U to 
> connect the HV from a PIG to the TC where the PIG is remoted from 
> the TC.  This resonance can cause a higher voltage standing wave on 
> the PIG end of the coax.  Dr R has suggested stripping the outer 
> braid of the coax to minimize the transmission line effect,  It 
> seems like to me that doing so changes the characteristic impedance 
> of the cable and doesn't really eliminate the problem.
>
> I was wondering if anyone has experimented with adding a series RC 
> termination to the pig end of the coax to effectively terminate the 
> coax. The C could be a string of C's to get adequate HV capabilities 
> and the R would be 50ohms if the shield wasn't removed or say 300 
> ohms if the shield was removed.  The RC time constant would be set 
> to be higher than the resonant frequency of the TC and yet low 
> enough to effectively terminate the coax for the high frequencies 
> where the coax length would resonant.
>
> Gerry R.