[TowerTalk] Common-mode choke

[Jim Brown]

On 5/19/2014 2:21 PM, Steve Hunt wrote:
> Jim,
>
> I don't disagree - I just don't consider a "Q" of 1.3 to be 
> particularly high for a choke! 

Nor do I, but the #61 chokes I've measured are in the range of 4-5. 
Compare the data sheets at the beginning of the Fair-Rite catalog for 
#31, #43, and #61. For the first two, u'' is greater than u' by a factor 
of about 1.6 in the range of 30 MHz, while for #61, the relationship is 
the opposite, and by a similar ratio.

Another point brought home by other comments in this thread. If the 
choke is sensitive to the stray C of the test fixture, it will also be 
sensitive to the stray in the practical circuit where it is used. 
Another reason to avoid it. N6BT, designer of the excellent Force 12 
antennas, pays a lot of attention to the sensitivity of a design to 
surrounding objects, height, etc. and works on his designs until they 
don't have these issues.

73, Jim K9YC