Filter Shape Picture ( Re:BITX20A board finished (report JL1KRA)


Hi, Robby and AH6GI

Thanks your comments,
My chasis preparation need more time. So, here is some bench
pictutes in progress.

In this weekend I am doing filter alignment.
Since I couldn't adjust TX carrier point correctly
with my 2 tone generator, I used Frequency Responce Mesurement System
(FRMS) and checked the BTX20A filter.
The FRMS is popular homebrew tool among JA QRPer using DDS and AD8307.
Without spectrum analyzer this is a good tool to see filer shape.

As you see the first pic, the bandpass has 10dB ripple.
DF5SF fileter pics shows similar shape. I suppose the
BTX20As are showing same character.

DF5SF changed C54,55,56 to 150,200,150pF from original 82,100,82pF.
I am now reaching 68,0,68pF to minimize the ripple. But
the skirt of the filter is worser than before to supress carrier.

May be this problem had been discussed in this list.
I am just arrived the point. I will check the previous messages

Junihi Nakajima JL1KRA

--- In BITX20@..., "ah6gi" <ah6gi@...> wrote:

--- In BITX20@..., "R R Robson" <rrrobson@> wrote:

Great, Junichi! Hope to see your pix soon.
Yes, please take pictures!

I too have to finish other work, an SB-303 with a bad LMO. This is an
easy fix but it takes time to get the LMO out, replaced, and then
align the drive mechanism.

de ah6gi/4

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