[UK-CONTEST] Stacking toroids

[Chris G3SJJ]

Thanks Ian, also Andy G4KNO, Tom G3OLB and Alan G0XBV. My understanding of toroids and 160m inv Ls has increased considerably. I have wound another 
unun on  a stacked pair of T300s and will try that. The system is only temporary for now to make sure I have coverage of 160m for the CDXC LF Challenge.

Later in the year I intend to re-do the vertical section making it around 65ft high but for now 55ft will have to do!

I'll reply individually to you all.   73 Chris G3SJJ


On 05/03/2012 17:31, Ian White GM3SEK wrote:
> 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).
>
>