A homemade interdigital filter for 1090 – how difficult can it be?
Following the results posted by TomMuc in this The Final Filter Shootout
post I thought I’d do some research on making my own filter(s). I’ve decided to try to make an interdigital filter as I have some of the bits already and they have a small insertion loss.
I found quite a few hacks had made filters for 23cm (1.2GHz) but many did not say how they worked out the dimensions. Further digging and I came up with some calculators.
These 2 are on-line
This one is a download
I decided to make a 3 stage filter following this http://www.i1wqrlinkradio.com/antype/ch41/chiave8.htm example but with dimensions calculated from above. I’ve already hit a bit of a snag as the 2 on-line calculators come up with different dimensions for the box
I will report results once I get something working.
Anyone want to chip in with thoughts/experiences?