During the last year Lundahl Transformers have developed a new line of Single-End to Single-End 1:1 interstage transformers.
When conventional design practice is applied to this type of transformers you easily get destructive capacitive coupling between the primary and secondary windings. This will reduce the HF bandwidth and increase HF ringing.
After a more thorough analysis we found that by changing the order and directions the sections were wound, the destructive coupling can be reduced, and the resulting capacitive coupling between the primary and secondary sections can be used constructively, to actually improve the HF bandwidth.
The new interstage transformers are: