A similarly surprising to me filter (when I first saw it without the background of why it works) is the crystal ladder filter (e.g. ) which uses a number of (ideally) identical quartz crystal resonators. All resonators have identical frequency response _when in isolation_ but when correctly coupled, the resonances shift to give an overall shape very different from the individual.
I think we have a similar structure here, so the key to alignment is isolating each resonator, without disturbing the intrinsic elements of the resonator itself, including the strays. Shorting the resonators on either side will drastically (!) affect their resonance - hence they will no longer couple strongly to the one being aligned. If you open-circuited them, that would work too, but seems rather more destructive.
-Iain Lindsay..
GM8LYQ
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On 09/10/2024 00:56, Douglas Denny via groups.io wrote:
...
The method you described shorting of the 40Mhz resonators in turn surprises
me that it is reported to work, but admit I fail to understand it at all.
If it does work - great !.. a new relatively simple new method to try.
They are relatively closely coupled however, and the image impedances
looking in and out at each resonator stage with the close coupling would be
badly affected if shorted I would have thought - which in turn would badly
affect the bandwidth shape I would expect.
