Re: Resonant measure

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "bob golding by way of Terry Fritz <twftesla-at-uswest-dot-net>" <yubba-at-clara-dot-net>

Hi all,
    In this months "electronics and wireless world" there is a design for a
meter
that reads very low values of resistance. I had a quick glance in the
newsagents.
Might be useful for checking the resistance of your tank circuit.
cheers
bob golding
Tesla list wrote:

> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Mddeming-at-aol-dot-com>
>
> In a message dated 1/23/01 10:13:17 PM Eastern Standard Time,
> tesla-at-pupman-dot-com writes:
>
>
> Thanks for the kind words. I don't think the LED technique works too well on
> the primary, because at resonance, the impedance seen by the generator is
> just the resistance of the primary coil (i.e., almost a dead short). I now
> use the AADE L/C meter described in the list about a month ago to measure the
> tank capacitance and then back-calculate the required inductance as
> L=1/(C*(2pi*f)^2) to match the secondary. Then I use the L/C meter to find
> that tap point on the primary. This is all done after disconnecting the tank
> capacitor and the power transformer from the coil. :-)
>          A second way which I used, before I had the LC meter and before
> smoking my non-digital HP 'scope, was as follows:
> 1. With tank cap reattached, short the spark gap.
> 2. Connect generator to the coil thru a 1K-ohm resistor and set generator to
> resonant frequency.
> 3. Monitor the voltage on the coil with your 'scope. Peak voltage should
> appear at resonance.
> A dip meter can also be used but I don't have one. This method does not give
> the exact point because the resistance of the spark gap under power is not
> zero as it is when shorted for this test, but it should get you fairly close.
> The formula for frequency is not exactly f=1/(2pi*sqrt(LC)). It is actually
> f=sqrt(1/LC - (R/2L)^2) /2pi.
> This means the exact resonance point is harder to find with L very small.
>   Matt D.