Measuring inductance, I am missing something obvious.

[ajlelectronics]

These are 88mH toroidal loading coils. I have a box full of them here and have used them before in my RTTY demodulators and have had no problems with bringing them to resonance with the expected capacitance. I was going to knock up a bandpass filter as per the diagram but a sample of four coils measure 1.3 mH or thereabouts which had me accusing the LCR meter of being junk. I set up a test circuit with audio oscillator into the 'scope and calculated the inductance to be about 1.3mH again, with resonance around 7600Hz with 0.133uF proving the meter right. I am aware that it can vary a bit with frequency, but I am using the same frequencies as ever, 1275 / 1445 Hz.

I don't believe that the box full is faulty, unless they were rejects and I don't believe that they have degraded in storage, being fully sealed.

Can someone see what I am doing wrong please, my brain has fried?

 

[RobCox]

There are 4 wires coming out of the coil judging from the pics. What do the second pair of wires do? Is it possible that they belong to taps off the main winding or to a second magnetically coupled winding? If one of the magnetically coupled windings is shorted, all you'll measure is leakage inductance that doesn't couple to the shorted section.

 

[ajlelectronics]

There are 4 wires coming out of the coil judging from the pics. What do the second pair of wires do? Is it possible that they belong to taps off the main winding or to a second magnetically coupled winding? If one of the magnetically coupled windings is shorted, all you'll measure is leakage inductance that doesn't couple to the shorted section.

Across white and black I am measuring 22mH, across the other pair, I measure the same, so I may have cancellation effects going on. However each winding should be 44mH. The part number is an 88mH.

https://ia801605.us.archive.org/2/items/g8mny_88mH_Coils_Explained/88mH_Coils_Explained.pdf

 

[RobCox]

Are the windings coupled magnetically? If so, reverse the connections to one coil. You may have the magnetic fields cancelling.

 

[ajlelectronics]

I'm being a Dillon clearly, thank you for helping me think about it...