Re: SSTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Chris Swinson wrote:

 > As I keep turning up the tube goes out, then comes back on again a
 > little brighter, then goes off again, then comes on a bit brighter...

 > My test coil was wound with 0.4mm wire. this one worked a lot better.
 >  The same "in and out" of tuning effect occurs.

Sounds like the driver is running at a very much lower frequency than
the coil Fres.

Either that, or the secondary coil is being excited at higher resonances
each time a harmonic of the drive signal hits one.

Remember, the driver is putting out a whole mess of frequencies, and
the coil responds at another whole lot of frequencies.  As you tune
around, when any two of these coincide, your lamp will reach a
brightness peak.

Try to pin down the correct Fres of your coils and make sure that
the driver fundamental is initially set close.  Use the scope with
a short wire pickup to sample the secondary E-field.  Make sure it's
a nice sine wave that matches the period of the square wave drive
signal.

Tuning can be acutely sensitive, and suggests some sort of automatic
control, either direct RF feedback, or some sort of control loop.
The challenge is to make sure the automatics settle on the right
pair of drive signal component/coil resonance, just as you are having
to do now manually.
--
Paul Nicholson
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