[TowerTalk] Windings on Amidon core

[jan elburg]

Dear Fellow TowerTalkers,

Trying to make a hybrid coupler (collins method) for 2 phased verticals.

Found a recipe in ON4UN's Low Band Handbook.

And what seemed an easy calculation, regarding the number of turns, is 
keeping me puzzled.

The used componets : 1 Amidon T225 core a a piece of copper wire.

The inductance should be 1.13uH for 7 mc/s.
Formula  L= 50/ 2*3.14*7.05

According to the formula for calculating the number of turns, in my case 
for 7 mc/s, it turned out to
9,7 turns making 10 turns.
Formula N = 100 * square root 1.13 / 120

10 turns on the T225 core gave 2,50 uH in stead of the desired 1.13 uH.
Measured with my MFJ259B.
I don't expect the MFJ very accurate, but 100 % off, I don't believe.

So where am I going wrong?