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



Original poster: "Gerry  Reynolds" <gerrytesla@xxxxxxx>

Hi Bob,

I think you are very correct here for an ideal lossless transmission line with a perfect open or short at each end. Any energy reverberating up and down the line will just "oscillate forever" at constant magnitude. However, if there is an energy source that has a frequency coincident with the natural frequency of the transmission line, energy could be introduced into the line and the voltages could grow.

Gerry R.


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

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.

50 ohms in series at the pig end of the coax, I would think, would have little effect since the pig HV impedance is the ballast impedance * N^2. However, if driving a capacitive load, a 50 ohm series resistance between the coax and capacitor, I think, would be very effective.


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