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Re: primary tuning

Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>

David Rieben wrote:

> 12x56 toroid ...
> .2 uFd for the primary tank...
> about 1260 turns of #19 wire on 12.75" x 48.5" ...
> a spiral of 12 turns of 5/8" OD ...
> innermost turn at about 15" in dimeter ....
> outermost (12th) turn at about 40" in diameter.
> the bottom secondary turn sits at 2 1/2" above the
> plain of the top of the primary coil

Hi David,

I ran your specs through tssp software and found a secondary
frequency of around 53kHz (given some guess of how high the
toroid is above the secondary), and found the tap needed to be
around 8 turns to resonate the primary at this.

The input parameters are well inside the range of numbers
for which JavaTC and tssp should give good answers (eg better
than 5%) so the fact that you predict 4 turns, I predict 8,
and you measure 10, is significant.   Something is wrong with
the parameters to the programs, and maybe also with the system.

I assumed the primary was 2.5" above ground, making the secondary
start at 5" elevation.  I assumed the toroid plane was 2.5" above
the top of the secondary winding, and that the winding was 48.5"
inches long.  I assumed 12x56 toroid means 56" overall diameter
made from a 12" diameter tube.  Also I assumed the coil was well
away from walls and ceiling.

1/ One of us has put the numbers in wrong - a factor of 2 error
between JavaTC and tssp is inconceivable for this size coil.
2/ There'll be a good reason for the error.

1/ We've both put the numbers in wrong.
2/ You've got an open circuit string on the primary cap (MMC?)?

- Check my assumptions above.  Is your toroid higher?
- Can you measure secondary inductance? I predict 119mH.
- Check primary C really is 0.2uF.
- Can you measure secondary Fres?

Rest assured, there *will* be a good reason for this discrepancy,
it will interesting to find.   I would like to see predicted and
measured tap points be within half a turn.
Paul Nicholson