"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.

Owen