Re: BPF too good? #filter


Adrian Scripcă
 

Hi all,

I also get a good IL of ~1dB when properly tuning the 40meter BPF version. I used a HP70000 series SA+TG combo for characterising; please find the plot attached.

All the best,
Adrian, YO6SSW


On Wed, Jul 8, 2020 at 11:28 PM ajparent1/KB1GMX <kb1gmx@...> wrote:


I really hate the on line editor as it has enough lag to get old versions.
(groups IO and net issue).

Seems there is a lot of mixing of LPF and BPF, they are not the same thing
and expected result is different.

For LPF loss should not exceed  .5Db in the pass band is expected and correct.
Its curve for S21 (through loss) should be mostly flat from some low frequency
though the band to the corner frequency and then a slope down to -50db
or greater.  Lumps or steps indicate wrong values or grounding issue as
well as lumps and steps in the region that is sloping should not be there.

For band pass the band width and loss will vary from band to band but
under 2db (s21) is nominal for the filters.  One must use a wide enough
sweep to insure all resonators are in the band pass and there are no
external peaks that would result in excess loss.   Note he position of
the input and output links should be the same relative to each other
and nearest to the cold (grounded) end of the inductor for both best
S11 and S21.  Reminer if measuring S11 the far end of the filter does
have to be terminated in the design resistance (50 ohms for these).

Allison
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