> -----Original Message-----
> From: topband-bounces@contesting.com
> [mailto:topband-bounces@contesting.com]On Behalf Of Jim Brown
> Sent: Monday, December 27, 2004 6:50 PM
> To: topband@contesting.com
> Subject: RE: Topband: FT-240-77 Toroid Impedance R + jX Components
>
> I find Michael's data quite consistent with mine -- although I haven't
> measured any 77 material, I have measured the rather similar #78. Also, I
> suspect that Michael's instrumentation is considerably better than mine.
>
> Remember that with suppression, you want lots of R but relatively little X
> (because you don't want the X to resonate with the cable that you are
> choking, causing current to increase rather than decrease). Transformers
> are different, especially if you are putting power through them -- you
> want lots of X but not much R.
>
Jim (and/or others):
http://www.dellroy.com/W4EF's-Ham-Radio-Page/Ferrite_Data/Ferrite.htm
Help me understand how this translates to a practical
use at the feedpoint of a receiving antenna.
I want to provide a common-mode choke at the feedpoint of
a Beverage or flag/pennant receiving antenna fed with
RG-6 or RG-8X feed line for 1.8 and 3.5 MHz. Power is
not a consideration.
I've been winding 10-15 turns of the feedline through an
Amidon FT240-77 (2.4-inch #77 material) core. From Mike's
data, the large number of turns is providing a large -jX
component, in addition to the large resistive component.
For a common-mode choke, would I be better off:
1) decreasing the number of turns; or
2) Using a toroid of a different material; or
3) Eliminating the toroid completely.
4) Doing something else altogether.
73,
Jeff Maass K8ND
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|