Thanks to GW0OAJ for this article

The first hack seemed to work - so on to the second effort with the bread board 4 MHz Cohn Ladder......


The impedance matching LC network at each end being left alone, the three fixed shunt capacitors were swapped with variable ceramics of a suitable type:

Trimming the caps produced a -3dB nose of 1.16 KHz, and a ripple of just over 3 dB instead of the previous 8 odd dB.  The skirts were now down to about 8.9 KHz at -90 dB.  Insertion loss remains at a very low figure....   -10 dB being the zero loss figure, choose your own interpretation from the nose plot!

Conclusion:

Now too narrow for SSB, but a very nice filter for CW WIDE.  All in all, tidied up and reduced in size by better layout, it would be a very nice addition to a design for a hacked out cheapo set...  The proverbial single band junk box special :D

Xtal Ladder Filter part2

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