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Re: [TCML] Tuning a coil PLEASE HELP
It helps to understand the concept of how the frequency of the secondary
increases the amplitude of the signal your looking for. This is due to
equal and opposite reactance. The secondary has both L and C reactance.
The self resonant frequency will occur when the inductive (Xl) and
capacitive (Xc) reactances are equal. Reactance (X) is an opposition to
current in an AC waveform. If we remove that reactance, we no longer
have that opposition. Reactance is frequency dependent. Above or below
the self resonant frequency, either Xl or Xc will be dominant, but "at"
the self resonant frequency, Xl and Xc cancel out and we are left with a
reactance of zero (no opposition). There are still impedances
(resistive, dielectric, eddy, etc.), but no direct reactances. This
causes a maximum current characteristic within the coil. It's this
current increase that causes the voltage to increase on the scope when
Xl = Xc, and that occurs when the frequency of the generator is adjusted
to the self resonant frequency of the coil.
The fundamental frequency (f1) will not necessarily be the first rise in
amplitude, but it will be the greatest rise in amplitude. The reason why
is that there are harmonics above "and" below the fundamental. The
fundamental frequency however will be very clear when you see it. The
waveform on the scope will rise sharply and you will be forced to adjust
the volts per division on your scope to view the waveform in it's entirety.
And yes, when you adjust the generator frequency, the width of the
signal per time division will increase and decrease. However, when you
hit and even get near the resonant frequency of the resonator, the
amplitude will shoot up. How sharp (or narrow) that signal is will
depend on the coil.
Use the 20V output on you generator (more signal for the coil). All
scope probes are shielded. This shield is a braid at signal ground
potential. The black clip should connect the scope and generator signal
grounds together (not AC ground). Your diagram is correct. It's a matter
of sweeping the generator to the correct frequency. Put the generator on
a "pulse" output (square wave). Don't rely to heavily on the frequency
meter (it can pick up fundamentals easily and give false readings).
Simply use the generator and scope. Then increase the generator
frequency into the kHz region and begin increasing the frequency slowly
while watching the scope waveform. You can put the scope on Auto trigger
for this. When you near and attain the resonant frequency, you will see
the scopes waveform spike in amplitude. Attach a 20" length of wire to
the probe end and just let it hang down and place the probe about 30"
from the coil to start with. The reason I say "start with" is that the
probe itself can influence the frequency a little. The further away you
are, the less effect the probe has (probe loading). But for what your
looking at, as long as you don't directly connect the probe to the coil,
almost any distance within reason will work.
Andrew Robinson wrote:
So I've asked for tuning help before and one or two people responded
with a link which was somewhat helpful... but now I need to refine
What im asking from the list now is two things, one question and a
confirmation on setup...
First, the general question which applies to all tuning setups. The
link I was sent to learn to tune the coil can be found here:
In this explanation (and any other explanation out there) after you
setup everything you are supposed to turn up the frequency on the
signal generator until the amplitude on the scope reaches a max. At
this max is your resonate frequency. Um........ I'm no electrical
engineer but when you change the frequency shouldn't the sine wave get
longer and shorter (Freq modulation) not get higher (amplitude
modulation)????? What am I doing wrong because when I setup the test
and do exactly what they say to do I dont get their results (amplitude
modulation) I get frequency modulation as expected....... PLEASE HELP
See these links to my server for diagrams of my setup. What I really
need is an explanation of physical setup, not schematic.
Secondary self resonance: http://host.atomiklan.com/tesla/scope1.PNG
In this first setup the signal generator has two ports. A 20v and
5v. Which should I use? Also each ports probe has red and black
alligator clips. Red goes to base of secondary and black goes where?
Is this diagram correct?
Primary self resonance: http://host.atomiklan.com/tesla/scope2.PNG
In this diagram I just think everything is wrong. Can someone
please correct my diagrams. Thanks
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