SOTS 87 7 wrote:Yes, at the moment, we are still in the ''playing around'' with it stage at the mo, obviously if we find something that basically works we will upload it and share the result. mind you, it seems ok as is oddly enough. Maybe an external LPF perhaps?
I had wondered how it would perform, with the original LPF. What I think you're perhaps seeing, are the combined effects of some useful inherent cancellation at 2f (due to the push pull design), with the LPF probably just starting to develop a reasonable amount of attenuation by 3f.
As you said, an external LPF is one way to improve performance. Or, I think component values from one of the "standard" Band II LPF designs (like the Stephen Moss design I posted earlier in the thread - just as one example), would transplant quite well onto the provided PCB; in place of the existing LPF. Turn each coil by 90 degrees, so that they're lengthwise across the gap, and still 90 degrees to each other, and it looks like you should be able to get the inductor length where you want it.