I built the direct conversion receiver described on the Soldersmoke blog a while back but ran in to several problems. The audio chain was very unstable and, perhaps ironically, the audio output level was very low.
Hackaday has also been covering this receiver project.
After some very enlightening discussion on the latest podcast I went back and re-built the audio amplifier chain.
One insight was that the gain of the three stages depends on the gain of the transistors and testing mine I get hfe of 350 which is up at the top of the range and might have helped with instability. The other insight was that there are bad 1K:8R audio transformers around and I suspect mine is causing low output audio.
Finally, I was unsure about how much drive a diode ring mixer needs. On the podcast they mentioned +7dBm which should be measured into a 50 ohm resistor and not into the mixer. I hadn't done that before. My VFO put 0.8V into 50 ohms which I calculate to be about +8dBm so just right.
I've just had a tune around 40m and can hear stations from all up the east coast quite well. Distances over 1,000km. (Although the lack of AGC means my ears hurt sometimes).
VFO tuning is very sensitive but I know things can be done about that. Actually, I love this VFO with the PTO tuning.
Note that while I have built the band pass filter I don't find it is needed at my home so I've left it out for now.
Thanks again to Bill, Dean, Pete and Hackaday for the prompt to have another go at this amazing home brew project.
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