[UK-CONTEST] Stacking toroids

[Ian White GM3SEK]

Chris G3SJJ wrote:
>I want to stack a couple of T300-2 toroids for a project I am working 
>on. A couple of questions -
>
>1 - Should each toroid be wrapped separately or should the non-painted 
>side of each touch each other and then the whole unit wrapped?
>
It doesn't matter with dust-iron cores.

>2 - The finished component will be a 4:1 transformer to match a 160m 
>inv-L. Currently I am using one core which already had 14 turns bifilar 
>wound as 4:1 balun but I have just altered the connections, so that one 
>free end is grounded, the other free end goes to a series C and the 
>centre tap goes to the Tx. It works well, tuning nicely with the C, 
>although the core saturates at a specific power area, hence stacking. 
>What are the relative merits are a straight winding against bifilar.
>

It is generally best to use closely-coupled bifilar or trifilar windings 
wherever you can. If you spread a single winding all around a large 
toroid, you are relying totally on the magnetic coupling through the 
core, which isn't particularly good with low-mu dust iron. On the other 
hand, that is often the best material to avoid saturation and heating at 
high power.

For what it's worth, a 50:22 ohm (3:2 turns ratio) transformer for 
80-160m worked well here with somewhere around 14 trifilar turns on two 
stacked T200-2 cores, all held together with fibreglass tape (Farnell).


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek