Hello Alan, Jay and Stefan,

Thanks for the replies. When I say "gets hot" it's not mad hot, a
cheap IR gun shows about 68 to 75 degrees Celcius, but I don't like
unattended things that get hot, for obvious reasons :)

I think I have a spare toroid like the one the filters are wound on
now, so i could stack a pair for the centre one. I am still unsure
what the down sides of air cored ones might be, increased physical
size and escaping magnetic fields that may interact aside. I am sure I
could find a 4.5 or so inch diameter former to try one on if it has no
down sides I am not understanding.

I can have a fiddle as my loading coil has started to come loose on
its plastic bin former, so I am off air for a bit as I will take this
opportunity to add a motorised variometer to allow in shack tuning of
it, which will be a lot more civilised in the cold and wet.







Thursday, March 8, 2018, 1:55:20 PM, you wrote:

> Chris my take on this.....not having used this level of power at LF.....if
> the core is gettting hot it is not providing a particularly high Q !! My
> line is that LPF are best made with air cored inductors, the values required
> are not so high as to need ferrite. (see MRF and YXM filters) It does mean
> care in layout to avoid coupling between the stages.  You may even be able
> to use a non-magnetic toroidal core!  Current sensing transformers at Rugby
> GBR 16kHz  (similar to the transformers in Jim Moritz scopematch) were wound
> on discs of Tufnol  (SRBF)

> One thought I dont know the answer to.......magnetisation is not a linear
> effect, if you are getting heating you are into the saturation 
> area......what does his non-linearity do to the signal ! It may even 
> compromise the effect your are trying to obtain ......actually generating
> harmonics??

> Alan
> G3NYK

-- 
Best regards,
 Chris                            mailto:[email protected]