https://hackaday.com/2026/07/02/diy-si5351-radio-tunes-in-sw-mw-and-more/
There are some really cool features in this receiver: There is an ESP microcontroller and an Si5351. There is the rotary digital dial that we had been working with. There is an NE602 mixer and a receiver that is sometimes (SDR mode) direct conversion and other times (Radio mode) a simple superhet with an 455 kHz IF. Wow.
There are really two receivers in this box, and AI kind of confused them. When I asked what the IF was, Gemini told me that there was no IF - it was, they said, a direct conversion reveiver. But no! In the quickly displayed schematics in the video, we see an IF amplifier and what appears to be two IF transformers and a BFO at 455 kHz. So at least in the "RADIO" switch position we see a superhet. The VFO freuency fed into the NE602 is 455 kHz above or below the signal frequency. If they had a BFO on they could listen to CW and SSB in the "Radio" position (it would not be single signal -- there is no sharp filter in there). But even wthout a BFO, in the RADIO mode you could also listen to AM signals using the envelope detector in the IF strip.
Things change when you throw the switch to the SDR mode. Much of the IF/Demodulator board is turned off. The Si5351 now feeds the signal frequency to the VFO port of the NE 602, turning it into a direct conversion receiver. You could feed this signal into your SDR but you would not get image rejection. For this you would need I and Q signals to go to the computer. This receiver provides I and Q output from the Si5351, and it is this that you need to turn that computer into a true single signal, image-rejecting receiver.
Thanks to Hack-A-Day for alerting us to this, thanks to Mirko Pavleski for building this receiver and showing it to us, and special thanks to Hans Summers G0UPL for cracking the code that let the Si5351 produce the stable I and Q signals needed in SDR receivers like this. More on this tomorrow.
