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Re: [TCML] My woeful RF ground experiments and lots of questions.



Jeremy Scott wrote:
Lots of ways...

How big is your coil? NST or Pole Pig sized?

It's a potential transformer, rated 1500VA but I'm told it can go as
high as 4000VA or so, so 'in between an NST and a pole pig'

One of the best ways to make an RF ground is to build yourself a counterpoise... Make a carpet or mat of chicken wire (aviary
netting) that has a radius about equal to the height of your
topload above the ground (e.g. if your topload is 3 ft off the
ground, make it 6 feet in diameter).

This is definitely doable. I've never heard about such an apparatus
in coiling, I'll investigate it further. Does anyone else on the list
use this?

Jeff Parisse published a picture a few years back of one of their big coils running out on a dry lake bed in the desert (where you can't legally drive a ground stake, and the "ground" isn't very conductive anyway). He used a sort of "star" made of rolled out chicken wire.





Not only does this provide a nice short path for RF to get back to
the base of your coil, but it also forms a big capacitor to "real"
earth, so that any RF current flowing outside can also flow back to
 the secondary.

Hook the counterpoise to your electrical safety ground (usually at
the coil, e.g. if you have NST, and you ground the case of the NST, ground to the same place.

So do I still need earthen ground rods for the electrical safety
ground.

Nope.. the "green wire ground" should be sufficient.  All the safety
ground does is make sure that if a person is touching something
(grounded) and your gear, that there's no shock hazard. Generally, the
safety ground should be big enough to carry the fault current that will
trip the breaker/blow the fuse, etc.


My potential transformer isn't at the coil, it's several feet away
and it's ground screw attachment (outer metal casing) is by the
primary 120V input side. Do I ground that to the counterpoise instead
of the green wire AC ground coming from the wall?


Outer casing gets grounded to the greenwire ground. Counterpoise gets grounded to greenwire ground, as well. The latter connection can have an RF choke/filter on it (to keep RF out of your electrical wiring)




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