Projects

My Projects

Direct Conversion Receiver Project 40m

This started out as a MRX 40 DC receiver using the NE602 mixer. The MRX was a simple receiver project printed in an issue of QST some time ago. I build the receiver and it worked however I could only get a few KHz of bandwidth using a crystal and a 1N4001 diode as a varactor tuning diode. The receiver sat on the shelf for years and this summer I had desire to make a few improvements.

One issue was low audio output and some oscillation/distortion from the audio circuit. The LM 386 is a fine audio amplifier however in its "high gain" configuration I have had some issues. I reduced the gain of the LM386 and added a simple audio amp/buffer circuit between he output of the mixer and the LM386. That along with better grounding solved the audio problems and i now have plenty of audio gain.

I wanted more bandwidth so I added a VFO circuit after removing the VXO circuit that was described in the QST article. It was simple to do and I had all the parts on hand.