[TowerTalk] Fair rite materials for choke baluns

[Jim Brown]

On Sun,7/3/2016 10:05 AM, Steve Hunt wrote:
> The #52 mix is readily available in size "240" toroids 

I didn't find this part in the Fair-Rite catalog because the assigned 
part number is for an inductive component, not for suppression. Many 
ferrite materials are useful as inductive components at lower 
frequencies and as suppression components at higher frequencies, so your 
measurements are not surprising given the material specs (see p 11 in 
the 17th edition of the Fair-Rite catalog).

BUT -- Fair-Rite controls specs based on their intended use, so 
inductive components are controlled for inductance, but NOT for loss 
impedance, and suppression components are controlled for suppression 
impedance and not for inductance. For example -- you can buy a #43 
2.4-in o.d. toroid controlled for impedance as Fair-Rite 2643803802. The 
same size #43 toroid controlled for inductance is 5943003801.

This may seem picky to those who have not worked in component 
manufacturing or as a circuit designer, but those of us who have 
certainly understand the difference. Some components come off the 
production line with relatively wide specs, and are sorted by measured 
performance for one or more parameters. Those that meet one set of 
performance tolerance specs get one part number, those that meet a 
different set get a different one.

BTW -- it should be noted that Fair-Rite does sell some #61 parts with 
suppression part numbers, but NOT the 2.4-in o.d. toroid. They made the 
right call on that one -- #61 is not sufficiently lossy at HF to be 
useful for suppression because the Q of the circuit resonance is too 
high. They DO sell smaller #61 components for suppression. They ARE 
lossy enough at high VHF and low UHF to be effective for use at those 
frequencies. For example, a single 0461164181 clamp-on resonates around 
450 MHz, and multiple turns through it would move the resonance down to 
about 2M.  0461176451 resonates around 250 MHz, and two turns would move 
it down to about 2M. In both cases, Z at resonance would increase by a 
factor of 2-3.

73, Jim K9YC