Hi Mike, welcome back! I am glad you are checking, as it is so easy to make mistakes.

There is little difference, really, between what you and I say if we take into consideration the fact that for

**powdered iron **(low mu values)

**Al **is normally given in

**uH/100 turns units**, while for

**ferrites **(high mu values)

**Al **is normally given in

**mH/1000 turns units**,

**uH **(microhenries) being 10^-6 Henries

and

**mH** (millihenries) being 10^-3 Henries

Therefore coil turns

**N** can be calculated as follows:

**N **= 100 * SQRT(

**L[uH**]/

**Al**) [1]

or

**N**= 1000*SQRT(

**L[mH]**/

**Al**) [2]

If we now take [2] (the one you apparently use) we see that to get inductance

**L** the correct formula is:

**L **= (N^2)*

**Al**/(10^6) where

** L** is expressed in

**mH** and

**Al **is expressed in

** mH/1000turns **.

In order to compare with previous work done with powder iron cores, I preferred to express the Al value in uH/100 turns, coming to the value of 118,000 which is equivalent to the value of 11,800 when expressed in mH/1000 turns.

Now for the difference Al between rated value (

**Al=2,200**) and value found by me (

**Al=12,000**) the reason is I made a mistake in mentioning material 43, while in fact I was using material 73. In other words the binocular cores measured are:

**BN-73-202**, with a rated

**Al = 12,000 +/-20 %**. Additionally the rated tolerance of +/- 20% must be taken into account and furthermore:

Experience shows that this formula provides only a rough estimate of inductance. You will

need to actually measure the inductor on the network analyzer to determine its inductance

precisely. From: "Toroid Inductor construction"

And this is what I did, measuring the core both with an inductance meter (Monacor LCR-4000) and Q meter (HP 4342A) and obtaining identical results. To conclude it is good to know that the cited binocular core is capable of working as a wideband 1 - 20 Mhz impedance matching transformer with practically no losses and with a small number of turns.

Thanks again for your help, attention & assistance,

glovisol