[TenTec] Home brew crystal filter

[Katz Ajamas]

I got the frequency counter set up today and decided to hack a 4 pole Cohn
ladder filter. Crystals were only matched for  frequency. It worked pretty
well in the Eagle. However, the center frequency was off by a good bit. I
had to crank the pass band control all the way to the right to center the
filter.

The crystals are HC49US (shorty HC49) and came in a sack of 200 for $10
including postage from China. I went through 20 to pick out 4 at 9.0001kHz
and used 3 x 30pF caps to ground.

It's a start. Next step is a test jig to better characterize the xtals. In
the mean time I'll sort them all by frequency and pick out some that are a
better fit to the Eagle.

The $3(postage included) 50MHz frequency counter/crystal tester kit that
arrived yesterday works great. Assembly took about an hour. Many thanks to
Wolf DL4YHF for the PIC code.

73, -Bob ah7i/w4