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Spectrogram (80MHz bandwidth) accelerator for LimeSDR

Project description

# Spectrogram (80MHz bandwidth) with LimeSDR and GQRX

![alt text]( "Demo")

![alt text]( "Diagram")

## Install

This application comes in a docker image (Linux PC/ARM architectures).
Bootstrapping the image is handled by the ``spectrogram`` executable (```pip install spectrogram```).

_**Note:** Use pip3 on Rasbian. Also, Rasbian fails to add the executable to PATH, use ```/home/pi/.local/bin/spectrogram```_

## Local usage

Invoking ```spectrogram``` does following:
1. If needed, programs the local LimeSDR-Mini with proper FPGA image ( restore with ``spectogram --fpga_restore``)
2. Starts the local 'SoapySDR-Remote' server
3. Starts GQRX for spectrogram display

_**Warning:** You should cool your LimeSDR-Mini, especially the FPGA. It takes 2.5 minutes for FPGA temperature to rise from 30C to 80C, after which you risk damage!_

_**Note:** Works on RaspberryPi, but currently the GUI needs optimizations ([#8](

## Remote usage

You want to pair your LimeSDR-Mini with RaspberryPi. On the Pi, execute ```spectrogram --server_only```.
Now, on the monitoring device, execute ```spectrogram```. GQRX will start, if the Pi is visible to the monitoring device.

_**Note:** Network bandwidth is around 1 MB/s._

_**Note:** [LimeNet-Micro]( is ideal for remote applications - it has LimeSDR, RaspberryPi and power-over-ethernet on single board. Work in progress ([#9](

### Accuracy vs floating-point model

This is a fixed-point accelerator, accuracy against the floating-point model has been verified.

![alt text](


### How is 512 point FFT comparable to 131k FFT??
It's about how many samples are averaged. 131k FFT averages 131k samples - same can be achieved with 512 point FFT and averaging 256 results i.e. 512*256 = 131k.

![alt text](

In general you lose ~3dB dynamic range. Also, 512 point FFT is much worse at detecting narrow spectral peaks - this could be considered a feature or a bug, depending on the application.

### Cooling the LimeSDR-mini

Using a '~2mm thermal pad' and a piece of metal:

![alt text](
![alt text](

Using small heatsinks wont cut it:

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