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Allison,

Here paralleling of cap arose? due to sheer unavailability of good quality caps in pF range in local mkt. I wanted to optimise the filters to best possible extent on local components so that people assembling uBitx in future can do so with whatever in hand or in junk box. It is very helpful to know the impact of such substitutions on filter response.

I did try out some 8 and 10MHz filters based on half bridge lattice following the work of DL6ZB , OM Rolf here:

?

I found them relatively easy to make, matching non critical and impedance's? easily manageable.?

Also found some HC49U 4.43MHz xtals in my old component bin they must be at least 25+ years old from Philips from my post student and struggle days, matched them now? a lot of about 25 xtals and all within 80Hz,? Talk about Quality..!! I made one QER SSB filter its plot is attached. Planning to give a try to some QER filters on 4.915MHz saw a picture on net for an add on board for K2 based on this topology, but I too would prefer xtals in 8-9MHz range with former being more common value.??

As you recommended to avoid ringing sweep rate is kept very slow by keeping the sample rate high on SNA at 1000 samples it sweeps at about 20KHz per minute.?

More as experimentation goes on ...

TNX and 73

Rahul VU3WJM