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Re: resonance?

April 4 Chip wrote:


>
>Well, I scored well at the ham fest.  I got an oscilloscope, a frequency 
>counter, and a square wave generator (0-1Mhz), all for $80!  I also
>got a 0-300V meter, and a 0-5A RF (thermocouple type) ammeter.

Great catch ! 

> Last night I observed an
>interesting phenomenon that seems like it must be resonance.  I connected
>the red connector on the generator (can't say positive for ac :-)) to one
>end of a new secondary that I am slowly working on, and the other end I 
>connected to the oscilloscope probe.  As I worked through the frequencies,
>I noticed some interesting wave forms on the scope -- they weren't regular
>sine waves, but looked like a sine wave with various amplitudes.  Then, as I 
>continued adjusting the frequency, I got a very nice regular sine wave.  As I 
>increased the frequency, the amplitude of the wave increased up to a point.  
>Then the amplitude started decreasing.  This appears to me to be some sort
>of resonance, but the weird thing is that the frequency was 1KHz.  I expected
>about 4KHz, but found no resonance points there, or at least no "broad peaks".
>
>I guess the next step will be to put the counter on the system being tested
>so that I can "calculate" other resonance points.  Then I'll see what happens
>with the primary circuit when I get the primary circuit built.
>

Yes resonance works like that increasing up to point and then decreasing.

Where specifically did you hook up the scope? I'm guessing you put it
accross the output of your secondary coil.

Looks like you might be getting some standing waves, they can cause the
various amplitudes. What impeadance is the generator?

Here are a few other ideas.

Have you checked the signal generator out put for linearity across that
range of frequencies? At $80 dollars for all It might take exceptions to
loading the coil.

How much output are you driving the generator at it might be more linear at
a lower range or output level.

John