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Re:Hello,
Hi Bert (Schumann),
Welcome to the list. Here is a preferred way of checking for
secondary resonance:
Place the coil several feet away from other objects. Connect
the "hot" lead of the generator directly to the bottom of the coil.
Connect a couple of feet of wire to the scope probe and hang it
several feet away from the coil. Both the sig gen earth and scope
earth are left unconnected. For a good coil, the tune will be pretty
sharp. For real accuracy, isolation and *low* coupling of strays in-
cluding the aerial wire to the secondary are the key. To get anywhere
near an accurate unloaded Q measurement, the more coil isolation the
better and the generator ouput impedance should ideally be zero Ohms
(like a perfect ground - right?). For frequency check alone it is not
quite as critical.
> Hi, my name is Bert Schumann from Columbia Mo. This is my first e-mail
> to the group. I'm glad a group like this exists and that it wasn't hard
> to find! (Are there any other coilers in the mid missouri area???)
> I've built several coils over the past 4 years, just small ones (300
> watts). And am in the process of trying to get a larger one up and running
> (700 watts)., but low and behold I seem to have a knack for blowing out
> neon xformers (at least I didn't blow out an entire power station like
> Tesla did at Colorado Springs!!)
> Any way, I was woundering what would be the best way to test for
> resonant frequency in the secondary (Toriod included) if one had a
> variable function generator and o'scope available to use? I hear it is not
> such a good set up to just string a wire a couple of turns around the
> secondary and then hook it across the function generator with the o'scope
> placed on both the top and bottom of the secondary. The o'scope will
> actually change the resanant frequency some, but is this effect
> negligable? Is there a better way to test for Sec. Res. freq?
> And what about the primary? I was just planing on hooking all
> primary parts together in series with the function generator and o'scope
> (minus the sparkgap and xformer of course and probably throw in a
> resister in order to keep the function generator from strainin'.) I would
> then adjust the function generators frequency in order to find its max
> through put. Is this a satisfactory set up?
Connect the primary as a parallel resonant circuit (short the gap).
Hook the generator in series with a resistor of 10k upwards across
the coil (cap - should be the same). Now hook the scope directly
across the cap/coil ensuring that the generator and scope earths are
hooked together. Disconnect the transformer and chokes from the tank
before measuring (shorting the gap will accomplish this if the gap
is connected across the normal power source).
Malcolm