[RFI] Toroids for Common Mode Chokes on CAT5 Cables

[Jim Brown]

On Thu, 11 Dec 2008 08:43:53 -0500, David C. Hallam wrote:

>What is the smallest practical size for a toroid to be used as a choke 
>on CAT5 cables?  I have 4 cables and putting one on each end is 8 
>toroids.  Looking at the prices I have found, that is about $100 of 2.4" 
>toroids.

Depending length of the cable, you may not need chokes on both ends. Check 
out my specific recommendations in http://audiosystemsgroup.com/RFI-
Ham.pdf  It depends on frequency/wavelength.  

The common 2.4-inch o.d. toroids of #31 material cost less than $5 if 
you're buying in quantity as part of a group purchase. Appendix One of the 
tutorial above includes advice on how to do that. Minimum size really 
comes down to a mechanical issue -- can you get enough turns through it to 
achieve the needed impedance at the frequencies of interest. Some clamp-
ons will get you there, but you may need to buy in quantity to get a 
reasonable price. 

73,

Jim Brown K9YC