Every now and then I decide it’s time to homebrew a receiver. You may remember my attempt back here. Or even way back here. They never work. So this even more complicated, 3 transistor, 2 diodes, and audio amplifier IC definitely did not work. Again. Well sort of. Technically it is actually a receiver. Just not what I was hoping for.

See the electrolytic capacitor I am pointing out down below? And the resistor that is in series with it? If I touch either with my fingertip, while the circuit is live, radio stations play through the loudspeaker. These components form a loop from pin 8 to pin 1 of the LM386; these pins are the “gain” pins of this low voltage audio amplifier chip.

This is a lot like what happens back in my last receiver build attempt, except for this one, I needed to touch the potentiometer in order to pick up stations. I’ll repost the video from that build below so you know what I mean. Essentially I could remove the entire rest of the circuit and as long as I powered up the LM386 and touched the top of the potentiometer, I could hear a station through the loudspeaker.

I am not through debugging this current circuit or I would go into more detail about it. In fact, in preparing this blog, I can see I left one end of a capacitor floating. The cap in the arrow below should be sitting between pin 3 and pin 4 of the IC. Pin 3 is correct, but then you can tell instead of hitting the ground rail of the chip at pin 4, the other end of the capacitor is just freely hanging out in its own row in the breadboard. To be fixed! And if I make any headway, I’ll write up a more complete description of the circuit.

One of my most successful and useful builds is in action down below. This is the KM1NDY Voltage Converter that I designed out from scratch that uses 78xx series of linear voltage regulators in TO-220 packaging. The voltages are interchangeable, and for this receiver attempt I used a 5-volt 7805 chip. The power source is a 12 volt LiFePo battery. This system includes a replaceable fuse as well, as an attempt to minimize any potentially dangerous currents from reaching me when I accidentally short something out. This little device is actually quite handy! If I make another one, I’ll need to put a switch on it though.

Ok, now close your eyes if you are going to be squeamish, but it is probably too late. I just wanted to show the bloodshed that this ham radio hobby causes me. This cute little pattern of blood bubbles is what occurs when you send the pins of an IC socket deep into your finger. Don’t fret! I am okay!

So, yet another failure. But there is still some debugging left to do, so I won’t write off the entire project just yet. And there are some important mental successes. The first is that I can now start to see the various stages of a receiver circuit. They are making much more sense to me now. And I can see how you can work on each stage as a separate entity. I am already concerned that my antenna and tuning capacitor are not working properly. Or that there is not enough amplification at the RF amplifier stage. I have figured out inadvertently that the components of the audio amplifier stage work. I needed to substitute diodes, so am I not demodulating the AM properly? And I am understanding bit by bit how and what to probe, and with what instrument, to see what is working, and what is not.

Though not so secretly, I can’t wait for the day when I post a receiver build and it is actually a success. But I have always known that failure is not trying and failing. Failure is not trying at all.

That’s that.

KM1NDY