Topband: FT-240-77 Toroid Impedance R + jX Components

[Jeff Maass]

> -----Original Message-----
> From: topband-bounces at contesting.com
> [mailto:topband-bounces at contesting.com]On Behalf Of Jim Brown
> Sent: Monday, December 27, 2004 6:50 PM
> To: topband at 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