Electronics > Projects, Designs, and Technical Stuff
Narrow Band SDR Project
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radioactive:
An image of an SDR optimized for narrow-band project I've been working on for quite a bit of the past year.  It has evolved to this.  Just an image for now.  More later.

I planned on crowd-sourcing it, but I'm starting to think I made it too expensive.  For once as an engineer,  I wanted to not worry too much about cost and just do what I really wanted to do.  Got kinda spendy due to all the high-end Analog Devices/Linear Tech parts.


[edit]  add block diagram for the hardware.   (will attach diagrams for software later).

[edit] remove older block diagram
radioactive:
Now that I'm finished with the hardware design, I'm trying to get motivated to work on some block diagrams for the hardware and channel models.  I'll share those when I get them ready.  I put a video up demonstrating the wide (+/- 90kHz channel) and narrow (+/-10kHz channel).  The baseband filters before the ADC are switched capacitor, 8th-order programmable in 10kHz steps.  The MCU is an STM32H743  (Y version).   The device operates completely stand-alone, but I have it connected to the PC to record the audio output from the device and to display the RF waveforms being streamed over Ethernet/UDP in baudline.  The device has lots of CPU left over after demod for decoding digital signals stand-alone as well.  Both RF signals in the video were around -94dBm to the antenna port.   I zoomed in on the time-domain and XY plots on the second half.

The wide signal is from an FM radio station,  the narrow signal is from NOAA weather broadcast (about 70 miles away I think).

superH FM demod demonstration
https://youtu.be/HBXcUFW8yaA
awallin:
how many bits is the ADC?
16-bit good ADC and dual-channel could be interesting...
radioactive:
The I/Q signals are filtered separately and converted from single-ended to differential before being fed to the 16-bit converters on the MCU.  The ADCs on the stm32h743 really does live up to the datasheet specs.  83 dB of clean dynamic range for 16-bit, differential mode.  I'm using DMA for ADC in interleaved mode.  Both I/Q and I2S audio output utilize DMA with double buffering.  The front-end can demod a narrow FM signal cleanly from -116dBm to +22dBm  (with software AGC adjusting attenuators). I'll have more details when I get the block diagrams ready to go.
TiN:
I wouldn't worry much about cost of prototype, because it's easier to make something crappy and cheaper , but hard to get high-performance stuff. I'm sure there would be customers who ready to pay the price if the performance and features are in place, since commercial devices of similar capability are likely 10-100 times the cost of your design?
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