[Elecraft] LC Bandpass Filter for AM Reception

[Jack Smith]

When I looked at the feasibility of an LC bandpass IF filter for AM 
reception a few months ago, I concluded that it was not feasible with 
practical components.

The K3's 2nd IF is 15 KHz, so in order to be effective at removing the 
image response, the 8215 KHz centered bandpass filter must be, say, 
60-80 dB down at 30 KHz from center.

In order to achieve 10-15 KHz bandwidth at 8215 KHz, and be 60-80 dB 
down at 30 KHz from the filter center and to do this with LC components 
with a reasonable insertion loss requires components with Q values in 
the tens of thousands. (Typical crystals as employed in crystal filters 
have motional Q values in the 100,000 range.)

Other than using superconducting wire, I could not come up with a design 
that meets all these requirements.

Am I missing something?

Jack K8ZOA
www.cliftonlaboratories.com