[TowerTalk] Toroid Core Material Selection

[Michael Tope]

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 at arrl.net>
To: <keith at dutson.net>
Cc: <towertalk at 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 at arrl.net
> FN13fc
>