[TowerTalk] Baluns/tutorial/notes.

[Jim Brown]

On Sat, 22 May 2010 14:28:54 +0100, Steve Hunt wrote:

>It all seems pretty academic when I could shift the SRF by similar 
>amounts simply by changing the way the leads were dressed. As Ian said 
>earlier, a choke which achieves high resistive impedances is the only 
>way of ensuring a robust and repeatable design.

YES. And that is exactly why the #61 material is a very bad choice -- a 
high resistive impedance can be achieved for a relatively small frequency 
range. For most of the spectrum it is either inductive or capacitive, and 
can be cancelled by the common mode reactance of the transmission line. 

The #43 material achieves this above 5 MHz, and the #31 material achieves 
this from the AM broadcast band up to VHF. 

Another way of looking this is that chokes wound with #61 have Qs on the 
order of 10, while HF chokes wound with #31 or #43 have Qs less than 0.5. 

73,

Jim Brown K9YC