Bandpassfilter for 40 meter band (7MHz) with Toko Kank 3334 transformers.

Important: only for receivers. This filter can not handle transmitted power.

Band pass filters are used to effectively suppress strong interference signals (BCI broadcast interference).

This reduces the noise in the band, there are fewer unwanted mixing products and you can hear weak signals better.

Study: the effect of the value of the coupling capacitor.

Picture: ugly construction

Schematic:

First case: coupling capacitor = 1.8 pF

Results:

Result: Insertion loss is 10 dB at 7 MHz but at 6 MHz, there is already a suppression of 20 dB.

First case: coupling capacitor = approx 8 pF

(5 x 39 pF in series).

Results:

Result: Insertion loss is only 1.2 dB at 7 MHz but at 6 MHz, there is a suppression of 16 dB.