Yes, good suggestion, Raj. I just made some measurements
on a 2.4 inch O.D. type 31 Fair-Rite Products core that K9YC
sent me. 7 turns on this core will give you >1000 ohms choking
impedance from 1.8 to 30 MHz. My data shows that the
type 31 material is much better than type 77 material in the
same form factor (2.4 inch O.D. toroid). The impedance of
the type 77 material falls off pretty rapidly above 2 MHz,
whereas the 31 material seems to provide good series
impedance well past 30 MHz. Check with Jim K9YC
on sourcing it. I am not sure this particular toroid is listed in
the Fair-Rite products catalog yet, but somehow he
managed to purchase a few pieces. BTW, depending on
the size of the wire, I suspect you could probably get by
with a smaller toroid than 2.4" (I like the 2.4" toroid because
its easy to wrap big cables with connector thru them when
troubleshooting RFI).
73 de Mike, W4EF.....................................
----- Original Message -----
From: "Rajiv Dewan, N2RD" <n2rd@arrl.net>
To: <keith@dutson.net>
Cc: <towertalk@contesting.com>
Sent: Monday, March 21, 2005 12:36 PM
Subject: Re: [TowerTalk] Toroid Core Material Selection
> Ferrite 31 mix seems to be a good one for chokes.
> Raj
>
> --
> Rajiv Dewan, N2RD
> n2rd@arrl.net
> FN13fc
>
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