Tiny Counterpoise

[alan sailer]

So I am getting close to trying higher power testing on my mini DRSSTC and more questions are coming up.
Some I am able to search and can't find satisfying answers others I have not been able to get the right search terms.

First is counterpoise. It seems clear that building an optimal counterpoise results in huge areas of mesh/foil.
So my question is are smaller counterpoises worth anything? I'm thinking of a 1.5 meter square mesh.

Second, it seems to me that building a target (attached to the counterpoise) is a good way to "control" the arc
and to get a good idea of tuning progress. I see lots of ladders and chairs in test videos and I assume this is an
attempt to make a target. Is a target a good idea?

Third, do you do tuning at maximum voltage or creep up on buss voltage more slowly. It seems that you can
control things with voltage or interrupter pulse width. Any guidelines?

I am getting about two foot arcs to my garage door at about 120 volts and can go to 310 volts maximum.

Finally, since phase lead correction varies as the device warms up during a pulse, you can't have perfect
correction over the entire pulse. Which is what I am seeing. I assume that you want to have
the phase correction optimized at the end of the pulse when the current stress is highest.

Is this true?

Thanks for any input.

Cheers.

[davekni]

1.5 meter square sounds great for a counterpoise.  If it is down on your garage floor, capacitance to ground (concrete, reinforcing steel, dirt beneath) makes it more effective.  You could connect a sheet of aluminum foil from your counterpoise to garage door for even-better grounding.

I think targets are more often about measuring how far the coil can arc, but others should answer that for themselves.

My tendency is to be cautious, increasing voltage and on-time and current limit (OCD) settings each gradually.  Depends how much time you are willing to take.

Yes, set phase lead for maximum current.  A little extra lead at low current is fine.

[alan sailer]

David,

Thanks for the answers. That is pretty much what I needed.

The coil is working well. Even if it never got any better I am pretty happy with it as it is at 150 volts. I typically don't try for
best possible spark size, just something that looks interesting.

I also dislike stressing transistors.

Cheers.