Homebrew superheterodyne receivers/transceivers using a computer crystal ladder filter, BFO and VXO offer the combination of simplicity and stability. The key to this receiver pattern is the VXO. I know VXOs are so ’90s, and that I should embrace digital and start banging out DDS VFOs with Arduinos, eBay AD9850 cards and AdaFruit si5351‘s. I will soon, I promise. In the mean time I just want to explore computer crystal mixing schemes a little longer. Scratch-building a DDS VFO necessitates some new practices, such as getting the script you’ve picked from dozens online to compile and download to the controller, for the particular combination of display, Arduino and DDS chip in use. I’m not saying it’s too difficult, I’m just observing that it isn’t trivial, and if you get stuck you may find yourself limited in your options to unpick it. Crystals, on the other hand, are real, physical things, remarkable for their sharp resonant characteristics. And these days they’re almost literally a dime a dozen.