[TowerTalk] Windings on Amidon core

[Ian White G/GM3SEK]

jan elburg wrote:
>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
>
May I recommend DL5SWB's Mini Ring Core Calculator?
http://dl5swb.de/html/software_for_amateur_radio.htm

It has a large library of core data from many different manufacturers, 
including dimensions and paint color as an identity check.

If your core genuinely is a T225-2, your calculation of 9.7 turns looks 
OK.


>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.
>
Sorry , I don't have one (Tom?) but a measurement based on 
series/parallel resonance should be more accurate.


-- 
73 from Ian G/GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek