I loved the article! Even though I only understood about 1/3 of the technical details, I was honestly quite amazed at how “simple” was producing RF! The guy is using “sound” at 48kHz to produce the signals needed and then a Si5351A (signal generator for up to 200MHz or so controlled via I2C) to produce RF. I’m not sure, or don’t understand yet how the RF is being modulated, but conceptually is understandable! DSP is a field I want to dig deeper into, specifically DSP as it pertains RF.
The reference signal generated by Si5351A is used to clock two flip flops which I believe are used to generate a 90° quadrature local oscillator (LO) which enters a dual 1-4 multiplexer acting as a Tayloe quadrature mixer. And as you know, the nonlinear switching action introduces frequency products and allows frequency conversion.
This is a pretty clever system. The RF is low enough frequency that faster logic chips can be used effectively. I recommend getting yourself a cheap receive-only SDR for around 15 bucks and play with GNURadio, if you want to get more familiar with DSP for telecommunications/radio detection
Thanks! I think the limitation is in my knowledge and not in the article or schematics!
I have a rtl-sdr and I’ve played with gnu radio, but the signals that I had to explore were very limited! Apart from few remotes for fans and stuff around the house I only had fm radio and little more.
What I find very interesting from this is the possibility of taking a Si5351A breakout board, configuring it with I2C (I can do that), modulate it with something like audio and a mixer (I can code that… maybe) and plug that directly, likely through and attenuator, to gnu radio!
It would certainly be a lot easier to get a sdr transmitter, but I wasn’t aware of the possibility of modulating a Si5351A with a “simple” signal like 48kHz audio!
