A simple 80m DC receiver

Another dose of simple goodness! I recently built this little gem in ugly construction technology (directly soldering the components to an unetched PCB). I never built a DC before so, as I had NE602s in stock I thought this needs to be done!

To my amazement the sound quality is stunning! As the DC receiver only has a single mixing stage, not much quality is lost in the process..

Images

The tradeoff of course is that the direct conversion receiver does not make a difference of signals above or below the local oscillator frequency and so an image signal is heard in close proximity to the original when tuning. Not a problem when the band is not too crowded but it will be annoying otherwise.

Of course there are ways around the problem (by demodulating a 90deg shifted signal with a second demodulator and adding both signals after the mixer so the image cancels out) but then again, long live simplicity!

There are hundreds of designs on the net for this kind of receiver, mostly circling around the same two core components, a NE602 mixer and an integrated audio amplifier. One of the more interesting was this one as it adds an audio CW filter. 

What I do differently is that my input transformer is not tuned but wide band. The reason being that I use the receiver with my small loop antenna which is very selective by itself so there is no need for a tuned input.

I do have a problem though with feedback in the AF section which can produce a loud and annoying noise at times. I think I know where it comes from and I need to do some modifications to remedy. Once I am happy with the layout, I'll publish it here.