On 2/14/12 2:50 AM, Jim wrote:
Thanks every for the good replies. John, what is the difference between a RF ground and earth ground?
Rf ground is "the cold end of the secondary" and doesn't necessarily need to be earth ground "the ground you're standing on".
From a spark standpoint, there's no need for the secondary of the TC to be connected to physical earth: consider a jacob's ladder on a NST.. plenty of sparks, no physical earth connection.
From a "tuning" standpoint, the screen under the coil (or earth) serves as "the other plate" for the topload capacitance.
There's several reasons why you want some connection between the "bottom of the coil" and "the earth you stand on".
One reason is safety.. if someone is going to touch that ground screen, then you want it at "earth" potential. Likewise, if it's not at "earth" potential, charge can accumulate and you could get a spark from screen to ground, possibly somewhere it would be bad to have it. This connection can be high impedance (i.e. you don't need a big strap or cable.. it could even be run through an RF choke).
The other reason is that unless you're running in a full cage, your screen might be 95 percent of the "capacitor" but the surroundings around the coil will be the other 5 percent. You want the connected together because capacitive coupling can allow current flow and you want the current going somewhere predictable.
_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla