Power Spectrum Measurement¶
If you are looking for a very simple way to measure the power spectral density of a received signal with the AIR-T, you may like the Soapy Power Project. Soapy Power is a part of the larger SoapySDR ecosystem that has built-in support on the AIR-T. In this post, we will walk you through the installation of Soapy Power on the AIR-T and provide a brief demo to help get you started.
Take a Spectrum Using the AIR-T¶
Using Soapy Power, it is very easy to acquire a spectrum snapshot and record to a csv file. Sample rate, center frequency, and processing parameters can all be controlled via command-line arguments as you will see in the below example.
$ soapy_power -g 0 -r 125M -f 2.4G -b 8192 -O data.csv
Let's walk through this command. The
soapy_power command is the program being called. the
-g 0 option sets the gain to 0 dB. The
-r 125M option sets the receiver sample rate to 125 MSPS. The
-f 2.4G option tunes the radio to 2.4 GHz frequency. We set the FFT size to be 8192 samples using the
-b 8192 and average 100 windows using the
-n 100 option. Finally, the output file is defined by the
-O data.csv option. Following the execution of the above command, a file is recorded with the spectrum data.
To visualize the data, we will use Python's
matplotlib package with the following script:
import numpy as np from matplotlib import pyplot as plt with open('data.csv', 'r') as csvfile: data_str = csvfile.read() # Read the data data = data_str.split(',') # Use comma as the delimiter timestamp = data + data # Timestamp as YYYY-MM-DD hhh:mmm:ss f0 = float(data) # Start Frequency f1 = float(data) # Stop Frequency df = float(data) # Frequency Spacing sig = np.array(data[6:], dtype=float) # Signal data freq = np.arange(f0, f1, df) / 1e9 # Frequency Array # Plot the data plt.plot(freq, sig) plt.xlim([freq, freq[-1]]) plt.ylabel('PSD (dB)') plt.xlabel('Freq (GHz)') plt.show()
Resulting Power Spectral Density Plot¶
- Artificial Intelligence Radio Transceiver (AIR-T)
- AirStack 2.0.0+
- Internet connection (for install only)
On the AIR-T execute the following to install Simple Soapy:
$ cd ~/ $ git clone https://github.com/xmikos/simplesoapy.git $ cd simplesoapy $ python3 setup.py build $ python3 setup.py install
The AIR-T's driver for Soapy is "SoapyAIRT". To verify that your devices is connected, and the installation was successful, execute the following in the terminal:
$ python3 -c "import simplesoapy; print(simplesoapy.detect_devices(as_string=True))"
which will return:
$ cd ~/ $ git clone https://github.com/xmikos/simplespectral.git $ cd simplespectral $ python3 setup.py build $ python3 setup.py install
While not required, this will speed up the FFT execution.
$ pip install cython pyfftw