Jim Brown jim at audiosystemsgroup.com
Wed Jan 12 10:01:19 EST 2005

On Tue, 11 Jan 2005 22:12:21 -0600, Ron Feutz wrote:

>I think the answer is big torroids on the incoming AC, CAT5 and phone lines 
>to the digital convertors.
> From reading the archives, 2" #73 torroids appear to be right.

I've been doing considerable research on that, and can offer this advice. The 
Fair-Rite 2.4" O.D. toroids are listed in the catalog with #43, #78, and #61. 
I've also just received (and measured) samples of #31. 

For 160-40 meters, first choice would be 7 turns around #31 (if you can find it), 
second choice would be 10-12 turns around #43. The advantage of #31 is that it 
gives more attenuation over greater bandwidth and does it with fewer turns. 

The #78 material isn't very useful about about 4 MHz, and it takes 14 turns to 
get that high. The #61 material has far too high a Q to be broadband enough to 
cover 160-40, and it would take more turns than you could wind. #73 is a nice 
material, but is used only for much smaller beads. 

Now, to prioritize which wiring should get the chokes first -- I would look for 
obvious pin 1 problems and hit those first. If you want to go brute force, do 
them all. The advantage of this size of core is that you can get a lot of turns 
through it, often without taking off connectors. 

BTW -- choking the Ethernet cable will also kill some of the common-mode trash it 
radiates on the ham bands. 

Jim Brown  K9YC

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