Topband: Binocular transformer design

[Jim Brown]

On Sun, 4 Jan 2009 18:54:37 -0500, Dan Zimmerman N3OX wrote:

>I think you'd find it hard to measure the difference even with good lab
>equipment.

Ferrite chokes are VERY difficult to measure with reasonable accuracy. 
Some of the difficulties and a couple of good measurement methods are 
described in the tutorials on my website. The principal reason is their 
high frequency equivalent cicuit, which is a parallel resonant circuit 
that has very small values of capacitance, and a fairly large 
resistance. 

Fair-Rite, the mfr of nearly all ferrite parts sold to hams, has always 
had a great catalog, available online in pdf format. A little over a 
year ago they significantly upgraded it by adding multi-turn impedance 
data (for 1-3 turns) for many of their suppression parts. This data 
doesn't get you down into the HF range, but it does clearly demonstrate 
how inductance, loss from the ferrite, and stray capacitance combine to 
move the resonance down from around 200 MHz to the upper HF range. 

73,

Jim Brown K9YC