Hello.
I have just tried a method of tuning the coil using a 'scope and signal
genny, that was suggested in the archives by Antonio Carlos M. de Queiroz .
I had already tuned it in the 'normal' fashion of injecting a signal in the
base of the secondary and hanging the probe close by. The secondary & toroid
were mounted in their usual place but the SG was left open circuit to
avoid the primary LC affecting things. I also tried it with the
secondary/toroid well away from the primary just to 'be safe' and the result
looked on the scope to be the same.
I do not have a frequency counter so I get the resonant peak on the scope,
and then connect the scope across the signal genny to get a truer result of
the frequency rather than reading the [rather course] dial. So small
differences won't show as the scope's 'eyeball' resolution is limited to
around 0.1 divisions.
I had also hung a piece of wire to the toroid to simulate a streamer. [The
difference between simulating a streamer and without one a drop of around
18kHz - 156.25 down to 138.88 kHz a drop of 11.1%]
The primary was then checked with the SG shorted and the genny and 'scope
across the inductor/caps. The secondary was removed completely for this part
though. After some adjustments to the tap point, both resonant frequencies
were the same [secondary with a simulated streamer].
I then tried Antonio's method of placing a 1.5 ohm resistor across the gap
and connecting the signal genny in parallel to it running at 1Khz square
wave output. The secondary and top load were connected and back in place,
whilst the NST and Terry were disconnected. The scope was placed across the
primary coil.
The resultant trace can be seen here:
http://homepage.ntlworld.com/follies/temp/scope.jpg
It looks like it may be correct as I can see what I presume to be the
ringdown, but I remember seeing a scope trace somewhere else on the web
where the abrupt sharp Y axis rises that I have, were replaced with more
gradual 'ringup' shapes, so I wondered what anyone else on here thought.
Both my 20 year old scopes are the limiting factor most likely as decreasing
the time base makes the trace even more noisy and unreadable.
As a point of interest the signal genny output was around 15 - 20 volts and
the scope timebase is 0.2 millisecond giving what I suppose [bear in mind
that the primary was running on 15 volts with no spark gap needing to fire]
would be an equivalent break rate of around 1/( 2.4 x 0.0002) = 2083 bps.
Regards
Phil
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla