Re: transmission lines from transformer /was: First Light HELP

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Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>


----- Original Message ----- : Re: transmission lines from transformer 
/was: First Light HELP


> Original poster: Kurt Schraner <k.schraner@xxxxxxxxxxx>
> > David Rieben
>
> At my big coil "Black & White", I'm using 2 RG213 cables of 10m (33') 
> length as feeders for the HV. The grounding sheeths are intact and 
> grounded at the RF-ground, close to the TC side. Each of the sheets forms 
> a capacitance of about 1nF with the central conductor. This conductors, 
> however are not connected directly to the SRSG, but via a local big 
> 1kohm/200W wirewound resistor each. By that way the sheet capacitance, 
> together with the resistors, form sort of a reduced "Terry filter" - I 
> like to believe ;-). In addition, a jacobs-ladder type safety gap is added 
> at the transformer side of the feeders.
>
> Before adding the resistors, I had some rare events of arcing at the 
> Xfrmer side, which might having had to do with transmission line effects 
> effect happening (Blumlein?), but never again since.
>
> Kurt

If you assume an open circuit or a short circuit at the transformer end and 
a short circuit at the sg end it difficult to see how the voltage on the 
line increases assuming any simple transmission line effects.  Perhaps it 
more than just a transient on a line effect.  For example if it happens 
that the primary transient period is harmonically related to the line 
length perhaps the voltage could build up.

I would expect that if you put a series resistor at least equal to the 
characteristic impedance of your cable which I think is 50ohms it will damp 
the line transients.
So your 1kohm resistors should work fine and will have the added benefit of 
reducing RFI.  As you say it forms a low pass filter or Terry filter.
This suggests the low pass filter R's should be mounted as close as 
possible to the SG.

Perhaps R's could be added on the primary side of the SG to reduce RFI from 
the line transients of the primary. They would have to be by passed with 
inductors so they primarily damped the HF transients. Don't know if 
practical solutions exist for this suggestion.

Robert (R. A.) Jones
A1 Accounting, Inc., Fl
407 649 6400