Direct Conversion Receiver - Band pass filter and mixer schematics

Here then is the circuit diagram for the band pass filter and mixer, or product detector. I stress that this receiver was never meant to be a simplistic incarnation, nor was it intended to be complicated. Each iteration was an attempt to improve performance with the least possible effort but sometimes this required more components.

Band Pass Filter and Mixer

Please take note of the comments on the schematic if you decide to make your own circuit board. If you want a commercially made board I may still have some left that reflect these comments.

I tried three trifilar transformers. The first was wound on a really small ferrite bead but I suspect it lacked inductance to work effectively. The second was wound on a larger bead, one that fitted over the top of miniature coax. It worked but I had some intermittent problems with it which I suspect was the result of the enamel insulation being damaged. So I wound a third on a miniature binocular ferrite and it worked a treat. My point is be prepared to try a few variations till you find something that works for you.


Regards
Richard VK6TT