[TowerTalk] Arrow had cheapest toroids

[Jim Brown]

On Mon, 24 May 2010 12:21:42 -0700, knormoyle at surfnetusa.com wrote:

>Arrow Electronics  had prices that came close to the 250 piece prices jim quoted, 
>for my small quantities. (www.arrow.com , just type part # into search)

Wow -- thats great news!  

>I'm going to try the bifilar winding with 14 gauge thhn (solid). Seems like the 
>cheapest solution with some so-239's and a plastic box. Jim gave that the thumbs 
>up with power, I think. Any comments on that? I might double stack the cores with 
>the bifilar turn count Jim gave. I suppose glass taping the cores is a good idea? 
>or unnecessary?

Do NOT double-stack -- that will change the tuning. Note also that my measurements 
are for #31, not #43. If you want to wind some with #43, Id be happy to measure 
them for you (Kevin is my neighbor a few ridges over) and can add them to my 
published data. I dont have any spare #43 cores laying around. 

>my antennas are well matched (<2:1), so I shouldn't be seeing a breakdown voltage 
>problem with the thhn? (with 1500W). I'm assuming the thhn pair is close spaced to 
>get close to 100 ohms.

I have NOT done extensive testing for long term power handling for bifilar chokes, 
but I saw VERY little heating when I stuck it in series with my Titan at 1.5kW for a 
few minutes of keydown. You should be fine. The primary failure mode is due to 
excessive common mode, which in turn is due to serious imbalance. 

73,

Jim K9YC