IQ FM Demodulator to Analog Audio

[FredWDaniel]

I am trying to piece together a simple programmable 30 MHz to 1300 MHz single-channel narrow-band FM receiver design using a ADL5387 and ADF4350 synthesizer. I presume a zero-IF or near zero-IF design would be the best choice.  I have looked at the simple IQ analog demodulators used in the uSDX Transceiver and the SuperH receiver, but neither seems a perfect fit for a stand alone receiver.  Each receiver would be programmed for a specific frequency and would use a custom made pre-selector front-end.  The output would typically be flat analog audio at 600 ohm line level of 0 dBm, but a option for de-emphasis would be nice.  The stand-alone receiver would be an open source hardware and software project.  I have looked at other designs using a high-performance stereo DACs like the MAX9860 and a STM32 processor, but cannot locate the necessary software to bring it all together.  Any thoughts? 

[David Hess]

I have looked at the simple IQ analog demodulators used in the uSDX Transceiver and the SuperH receiver, but neither seems a perfect fit for a stand alone receiver.

What kind of demodulator do they use?

The first thing which occurs to me is to use a Costas Loop for demodulation which provides FM and synchronous AM demodulation.

[radiolistener]

I think the most flexible way is to use some high speed STM32 MCU with DSP features.

For example there is cheap Chinese module with STM32G431CBU6:
https://www.aliexpress.com/item/1005005303669884.html

It has onchip ADC and DAC, they are 12-bit, but you can use it to implement test code and then add external audio codec for audio output with 24 or 32 bit dynamic range and (in case of needs) external 16 or 24 bit ADC to digitize IF.

I know that this MCU is able to do AM and SSB demodulation in realtime, but didn't tried FM.
Needs to check if it can calculate atan2 for 200 kHz IQ stream in realtime.

[glenenglish]

just use  an arctan approximation. there are lots of possibilities there. you might need to figure out what quadrant you are in.