I want to design a sensitive 3 stage receiver circuit for 40 MHz using BF998. Very narrow bandwidth (39-41MHZ) and maximum attenuation is required out of the band.
I need help in the following steps
Input filter design (type and order)
Biasing the BF998
impedance matching at input side .
Interstate matching
Output matching to NE612 mixer ic.
If you attempt to catch a certain degree of sensitivity, I recommend you to consider "Noise Matching" that will give you lower Noise Figure from that amplifier.
If the first stage of the chain is a Filter, the Insertion Loss of this filter will contribute directly into Noise Figure of the system so the first stage shouldn't have lossy elements.( the frequency is low so high quality compact components should be used to prevent high losses).