Hi!
I recently built a 455 kHz = 11 kHz down converter using a schematic that was sent to me by Bill (KE1GF). Bill was kind enough to give me permission to disseminate it, along with information about how to get the parts, and how to use it.
I think you will find it to be an extremely useful device, which you can easily build for around $20.00 (the cost of the parts)... and which works in conjunction with the existing sound card of (almost) any plain vanilla computer.
To see the schematic and the associated information... including a screen shot of the r.f. spectrum of an AMer, taken off the air with my receiver => Bill's converter => my computer => a freeware application called Spectrum Laboratory (that you can download from the Web)... go to my Web page:
http://mysite.verizon.net/sdp2/Best regards
Stu