Topband: measuring transformer core inductance

[Tom Rauch]

What are you trying to wind Steve? Odds are it has been done before, and
someone could help.

< It actually generates a 1 kHz signal for measuring inductance which
probably makes it worthless for measuring inductance at 1.8 MHz.  Is this
the case?>

It will be unreliable for measuring impedances except at or near 1kHz,
because that is where it makes the measurement.

 >My question to the group is what do you use to measure the inductance of
the windings so you know when you reach the desired ratios?>

Use an antenna analyzer like the MFJ 259 and some dummy resistors. The MFJ
259B reads inductance, resistance, and Z directly. If calibrated correctly
by MFJ it measures with good accuracy. The parameter you need is impedance,
not inductance.

> I cannot seem to locate website charts that show inductance/frequency
curves for the cores on Amidon or Fair-Rite websites.  This would help to
estimate where one needs to go when they wind up a core.>

If you are in a non-resonant transformer receiving (low power)  application
on 300kHz through 30MHz use a 73 material. As I recall it has about 25-100
ohms Z per linear inch of  "hole depth" on 160 meters. My website should
have something on this.

You won't find an "inductance" curve or formula for 73 material because Q is
unity at around 1-2MHz. Standard turns ratio formulas work fine for any
transformer with moderately low loss. Lossy transformers are not bilaterial
and will also not follow expected formulas.

Use the FairRite Products catalog data, don't rely on Amidon. Core resellers
like Amidon generally aren't nearly as accurate or reliable as actual
manufacturers for data or technical support.

73 Tom