I have a 300 long x 50mm dia. Schumann coil that measures 18.75KOhms.
I have no way to measure inductance. It has an annealed steel core 1M
long.

What capacitor value do I need to tune it to an 8Hz center frequency?

Thank you,

Tim

Are you quite sure you have no way to measure inductance? Even if you
have only an AC voltmeter and a signal generator and some capacitors,
you should be able to measure the inductance. One of the best ways to
"measure" it for your application is to try a capacitor and see what
the resonant frequency actually is; then adjust the capacitor (by a
factor equal to the square of the ratio of resonant and desired
frequencies) and try again, repeating until it's trimmed to the
desired resonance.

Cheers,
Tom


Tim Robbins wrote in message . ..
I have a 300 long x 50mm dia. Schumann coil that measures 18.75KOhms.
I have no way to measure inductance. It has an annealed steel core 1M
long.

What capacitor value do I need to tune it to an 8Hz center frequency?

Thank you,

Tim

I have no way to measure inductance.

To know what size Cap. you will need, you will have to have some idea of the
inductance. One easy way to check the inductance uses an AC voltmeter a
variable resistor (pot), and a low voltage 60 hz voltage source like a 120/12
volt transformer.
Hook the inductance and the variable resistor in series. Apply the 60 hz
source across the series combination. Adjust the pot until the voltage dropped
across the pot and the inductance are equal. Read the value of the pot, this
is now equal to the inductive reactance of the coil Xl plus that 18k DC
resistance you said you measured. From this you should be able to calculate
the approximate inductance of the coil, and the Capacitor value needed to tune
it to 8 hz.
Use L=(Xl+18k)/2*pi*60
and then 8^2=1/4*pi^2*L*C and solve for C.
73 Gary N4AST

"JGBOYLES" wrote in message
...
I have no way to measure inductance.

To know what size Cap. you will need, you will have to have some idea of
the
inductance. One easy way to check the inductance uses an AC voltmeter a
variable resistor (pot), and a low voltage 60 hz voltage source like a
120/12
volt transformer.
Hook the inductance and the variable resistor in series. Apply the 60
hz
source across the series combination. Adjust the pot until the voltage
dropped
across the pot and the inductance are equal. Read the value of the pot,
this
is now equal to the inductive reactance of the coil Xl plus that 18k DC
resistance you said you measured. From this you should be able to
calculate
the approximate inductance of the coil, and the Capacitor value needed to
tune
it to 8 hz.
Use L=(Xl+18k)/2*pi*60
and then 8^2=1/4*pi^2*L*C and solve for C.
73 Gary N4AST

Gary,
This sounds like a good idea. Only thing I would worry about is that given
the dimensions of the coil, it may be resonant below 60 Hz.

Tam/WB2TT

This sounds like a good idea. Only thing I would worry about is that given
the dimensions of the coil, it may be resonant below 60 Hz.

Hi Tam, Well, guess you are right, the self resonant frequency of the coil may
be below 60 hz and would make the measurements different, this compounds his
problem.
73 Gary N4AST