Simple Direct Conversion Receiver With MC3361 and LM386

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Magnetic materials and RF electronic components for amateur radio / ham radio.

I posted this simple direct conversion receiver under sponsored posts, as a way to say thank you to Andrei for the nice present. The kit used to be available at rowaves.com. Andrei – YO6TJJ sent me the kit to test the receiver. He seems to be passionate about bringing back to life older designs as much as I am. I like simple transistors circuits, he likes classic IC’s. It was a lot of fun building and testing this receiver and one step forward for me in my learning curve. This was my first direct conversion receiver.

The PCB board of the radio receiver kit has the same size of the one of a Pixie transceiver. I admire Andrei for his patience to design the PCB board and squeeze all those components together on such a small board. I thought I had patience, but clearly he is doing better in this matter.

THE SCHEMATIC

Andrei – YO6TJJ designed this simple direct conversion receiver with an MC3361 and an LM386. The circuit is based on the well known Lidia direct conversion receiver. This is a slightly improved and simplified version of the receiver. I always searched for a schematic based on transistors to start my first direct conversion receiver. The reason for that is because I wanted to understand all the stages and how they interact with each other. Clearly the receiver can be simplified a lot using integrated circuits.

Original Image Source rowaves.com

BUILDING THE RECEIVER

I only spent about two hours putting the kit together. That because I was also filming the entire process. Normally I don’t think it would take you more than one hour. This could also be build from scratch very easy. Since I will not design a PCB board for this one, I would recommend you to try a method that I started using lately. I always admired Paul – VK3HN and the way he is building his circuits.

You can check many of his projects on his blog page as well. To build the kit I also needed some other parts not included in the kit. A 4 Ohm speaker, 1 x 10K multiturn potentiometer for tuning, 1 x 10K for the RF attenuator, 1 x 47K for the volume control, some switches and connectors for power and antenna. I decided to also use a frequency counter module for this direct conversion receiver.

BANDPASS FILTER ADJUSTMENT

As shown in the video, for this step I decided to use the nanoVNA. I am trying to learn a little more about using this really nice tool. Once I was happy with the filter adjustment, I could continue with the rest of the project. If you don’t have a nanoVNA, you can also adjust the filter by ear really easy.

FREQUENCY COUNTER

I received this little frequency counter from my friend Nigel – ZL1NAY. I liked it a lot because of the size. Small and compact, makes it easy to fit in a small enclosure. I think I will have to order more of this as I am really happy about it. I have a feeling I will use this one in many other projects from now on. In order to use the frequency counter with the receiver, I had to build another board on the back of the frequency counter. The schematic is really simple, and it allowed me to pick up the RF signal from pin 1 of the MC3361 IC.

As you can tell from the photo above, the extra board is not so pretty. I made it in a rush as I was out of patience to see the receiver complete and working. As long as it does the job and it works, look is not always on the first place. Especially that once in an enclosure, no one will ever see it again to soon. You also have the schematic of the simple circuit I used to get the signal from the MC3361 IC to the frequency counter.

TESTING AND CONCLUSION

As a kit it was really easy to put together. Built from scratch should also be easy. The most time I think it would be spent to design the PCB board, unless you use mePads. In the video I explained a few modifications I made and the reason behind those. I really like the way it sounds and the size.

Besides the fact that it sounds and performs great, I also wanted to make a frequency stability test. I do this with all the receivers I build. So I set it to 3.780 MHz around 10.30PM… returning to check the frequency early in the morning at 8.00AM. The frequency only drifted to 3.781 MHz. I did noticed moments when it was going up around 3.784 MHz, but always returning to 3.780MHz after a short while.

I like the receiver and I must say Thank You one more time to Andrei – YO6TJJ for such a nice present. I will soon build a nice enclosure for it and have one more receiver on the memories shelf. I have a feeling that I will use it in the future together with an 80m band version of the Ten minutes transmitter. I still have to learn the code for now.

73 DE YO6DXE

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