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Re: mystery resonance

I was suspecting (hoping) that the push-pull output transformer's mystery resonance is causing or at least worsening the deep notch I have in my receiver BPF at 25MHz. I changed from WTST to a standard Guanella transformer with separate drain supply RFCs (I had another reason to do that, but the RF behavior of this arrangement is a lot more straight forward than WTST) and did the receiver sweeps. The traces looked unchanged. My BN**-202 core looked dull black not shiny so I assume I got 61 version (I received mine about 2 weeks ago). So, I think the mystery resonance in the output transformer might be something to do with the other winding styles on 43 but I don't think that is an issue with WTST or straight Guanella transformer on 61.

Incidentally, as a primarily high band CW guy, I used 61 core in several of my antenna feedline transformers and they also performed well down to 60m and 80m so I'm familiar with this material. I've always thought that 43 was a bit over-popularized even where other cores would work better. But in reality if the transformer is well designed, the performance difference between 43 and 61 in HF bands may be rather small. Another good ferrite material is Laird 28. This core is somewhat between 43 and 61 (more similar to 43 though).