This isn't much of an update on the actual project, but some fun I've been having with the bits I made so far. Since the point of this project is to make RF electronics accessible and fun I decided to build a little 20khz FFT spectrum analyser with a Teensy 3.5.
What's actually displaying of course thanks to the mixer is a 20Mhz signal. With the Si5351 this can go to 200Mhz with some sweeping and filtering, so almost UHF. When I've got funds for another component run I'll look for some higher frequency mixers because the 612 can only take an LO of 200Mhz, so taking 430Mhz down to 20khz is a bit of a big jump.
Of course what we already have here is a radio. Set the LO to the mixer from the VFO module to the frequency of the radio station (minus 20khz) and the teensy gets that signal on it's audio port. From there you can process the signal in software and output it to a speaker on the DAC. Before I start messing with that too much I want to box the Teensy up on a breakout module of its own so I don't have to deal with the breadboard and then add some variable gain amplifier and decoupling transformer / filter.
So that's the next thing on the TODO list - filters and amps! A BFR93 / BD90 low noise amplifier and a simple LM358 op amp for audio or other very low frequency signals.