The element14 community (shabaz) pointed me to a very neat SDR project using a RPI Pico.
I have a RPI Pico and lots of generic and jellybean electronic components.
So, I will have a go at building a copy of the open source project.
All of the projects schematics and documentation are available here:
https://101-things.readthedocs.io/en/latest/radio_receiver.html
I don’t have all the exact components used in the project.
I made the following substitutions with similar components I had on hand
The frontend low rdson analog multiplexer was replaced with a 74HC066 quad analog switch (plus a one hot decoder).
I also lowered the gain of the op-amp difference amplifiers.
On power up, the picorx software defaults to an LO frequency of 1.4085 MHz.
I used my signal generator to apply a 150 mVpp carrier with a frequency that sweeps from 10 kHz below the pico’s LO to 10 kHz above the pico’s LO.
I get wonderful sinewaves on the output I/Q channels:
The quadrature detector has significantly more bandwidth than I expected.
You will notice that for frequencies above the local oscillator the Q signal leads the I signal (and vice versa for frequencies below the LO).
The QSD’s response within 1 kHz of the LO is being partially rejected by the AC-coupled difference amplifiers.
The amplitude response of the I/Q channels is not very well matched (I will have to think about that for a bit)
More to experiment with, but impressive results for the simplicity of the project.
