----- 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