Subject: RESONANCE CLARIFICATIONS
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Tue, 4 Apr 1995 22:20:00 GMT
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CA> Subject: resonance clarifications
CA> The hook up was as follows:
3 <-- Secondary
Signal gen ----
CA> Note: Only one wire was connected to the generator output, even
CA> though there are two output jacks on the generator.
You need a 1K resistor in here somewhere to read accurate grid dips while
you are characterizing the secondary. My scope and generator are wired out
with BIN coax connections. I tie the shields together, an place the 1K
resistor in series with the O'scope input lead. I do not use a probe.
CA> The secondary has no top or bottom at this time.
CA> It is just a solenoid with no "top" capacitance.
Which is where you want to start and get your "baseline" or natural
1/4 wave resonate frequency.
CA> How would I check for linearity? Do you mean constant amplitude
CA> for a range of frequencies?
Not really necessary at all. 1/4 wave grid dips are not all ephemeral
or even difficult to find. Either they are there, or they are not. When
they are there, your scope reads just like an accident victim too late
to the ER...
While scoping the coil, the first (and only) flat line is the natural
1/4 wave resonate frequency of the coil. If you dial up the frequency
generator you will see dips in the grid further up, but no more flat
lines. The grid dips at higher frequencies are the natural harmonics
of the "fundamental note" as Tesla so frequently called it. The scope
will clearly show these harmonics resonate at a much lower Q than the
natural 1/4 wave frequency; the grid dips, but it does not "die".
CA> I don't know about the output voltage. I assume that there is
CA> probably very little current flowing.
You only need enough output voltage and current to be able to put a
good trace on the scope. Mismatched frequencies between the coil and
generator result with a very high base impedance in the coil. With the
impedance high, there is little current uptake, so the voltage peak
on the scope trace remains high. When the freq-gen is dialed to match
the natural 1/4 wave resonate freq of the coil, the base impedance
of the coil drops dramatically: the scope reads no voltage at all as
the coil is taking up all of the current.
CA> The signal generator has a 75 Ohm label above the outputs.
I wish I could help you here, my best guess would be that this refers
to the coax to connect it. Only a guess (and probably a bad one).
... If all else fails... Throw another megavolt across it!
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