[TowerTalk] Fair rite materials for choke baluns

[Jim Brown]

On Sun,7/3/2016 11:08 PM, Jim Thomson wrote:
> ##  Ok, Im lost.   I thought  we wanted  Z >  RS > XS .
> Put another way, RS ideally should be the same as Z... or as close as
> you can get to Z.   And  RS  should definitely be >  than XS.
>
> What is RP  ??

You really are resistant to studying what I've written. :)

Rp is the resistance in the parallel (RLC) equivalent circuit of the 
choke. Rp is the Z at resonance (the peak value), L is the value 
computed from Z at frequencies below about half of the resonant 
frequency, C is the capacitance that resonates with L. This is nothing 
more than the classic curve-fitting that I learned in EE classes in 
college 50+ years ago.

I put my measured Z data (magnitude only) into a spreadsheet (I use an 
ancient version of Quattro Pro because it is FAR better at producing 
engineering plots of data than Excel), and plot that measured data on a 
log-scaled graph of Z vs log-scaled of frequency. On another page of the 
spreadsheet, I compute and plot the equation for parallel resonance, and 
tweak the values of R, L, and C that most closely fits the measured data.

The parallel equivalent circuit is important for at least two reasons. 
First, it helps us understand the choke as a component -- as hams, we 
understand that any coil has stray R and C, and it will resonate. We 
also know that we put a coil into a circuit, resonate it with C, and 
control the resonance by the number of turns and by squeezing or 
spreading turns to control both L and stray C.

Second, knowing the values for parallel R, L, and C, we can insert them 
into an NEC model of our antenna system and find the common mode current 
and the common mode power dissipated in the choke (by setting power in 
to model to the TX output power).

73, Jim K9YC

On Sun,7/3/2016 11:20 PM, Jim Thomson wrote:
> ##  Ok, so the type 31  2.4 core we should be using for CM chokes is the
> toroid controlled for impedance... PN  2643803802    ??

In Fair-Rite's part numbering system, the 26 indicates a cylindrical 
core  (NOT a clamp-on) controlled for impedance, the following two 
digits 43 indicates #43 material, and the remaining digits indicate the 
physical dimensions (I haven't figured out that code).  So a #31 
material in a cylindrical shape would have a part number that begins 
with 2631.

> ## Good thing u mentioned the type 31 core  comes in 2 x versions.  I wonder
> how many folks have ordered the wrong part number in error ?

#31 material is NOT sold in two versions -- it's designed ONLY for 
suppression.