Owen Duffy wrote:
"J. Mc Laughlin" wrote in
:


I looked through saved messages and the only reference to type 31
ferrite (Fair-Rite) was in March of 2005. That reference had to do
with ignition wires.


Mac,

Whilst playing around with models of a Guanella balun, I did compare #31
sleeves with Walt's design using #73 sleeves over the range 1 - 30MHz.

My model of Walt's balun is at http://www.vk1od.net/balun/W2DU/index.htm
. I obtained different results to Walt's measurements, but I think that
is because Walt's measurements were affected by stray capacitance that
was worse than would apply to that type of balun in service.

I also modelled some Fair-rite 2631480002 sleeves and found a slightly
longer choke (12 cores at 25.4mm ea) was needed to achieve about the same
choking impedance up to about 12MHz, above which the #31 choke had higher
impedance than the #73 one.

Whilst I modelled these sleeves because they suited the application, I
have not seen anyone selling them in small quantities.


Mouser has them.. Don't know if they ship in VK land or not. Shipping
of what is basically iron bars is going to be punitive. FairRite has
distribution there (Specialised Conductives in Victoria), but perhaps
not retail. But, since one typically isn't looking to buy just one, but
dozens, this might not be a problem.

One should be careful about modeling these things.. that gets you close,
but parasitics are a real bugabear. K9YC's paper has actual
measurements on actual chokes made with a variety of cores (which are
decidedly non-trivial to make..)

Snelling's book is the tome of choice, if you can find it...