Towertalk
[Top] [All Lists]

Re: [TowerTalk] Ferrite beads for common mode current

To: "Tower Talk List" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Ferrite beads for common mode current
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Wed, 25 Jul 2007 18:27:11 -0700
List-post: <mailto:towertalk@contesting.com>
On Wed, 25 Jul 2007 18:04:21 -0700 (PDT), Rick Karlquist wrote:

>inductance no longer goes up as N squared.

It doesn't matter -- it's RESISTANCE we want, not inductance. 

But 6 meters IS a challenge for a choke balun (it's also quite a 
challenge to measure). As Jim Lux suggested, a multi-turn choke 
WILL work, but you'll need several chokes in series. A study of 
the data in the updated tutorial should help you design a suitable 
choke. 

A traditional "string of beads" choke using #31 or #43 cores will 
work fine on 6 meters. Probably the best bet is a string of two-
turn chokes using a short length of smaller coax (like RG8X) 
through a 0.45 i.d. core designed for RG8. One of the 1 inch long 
#31 or #43 cores should yield about 600 ohms on 6 meters. I would 
use at least six of those in series on the coax, with a separate 
2-turn loop for each. 

If you want to use RG8, use two of the "big #31 clamp-ons" listed 
in the tutorial, each with three turns through it. Each clamp-on 
needs its own 3-turn loop. 

When counting turns, that's the number of times the coax passes 
through the cores, not the external turns. 

For more details, see the tutorial.

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC  



_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>