change analysis plot to dB

Python_script/analysis.py

 import pandas as pd
 import matplotlib.pyplot as plt
+import math
 
 def extract_stable_data(datafile):
     datapoint = {}
@@ -46,15 +47,22 @@ def plot_temperature_sweep(start_temp, stop_temp, humidity, basename):
         phase_vars.append(datapoint['phase_var'])
         magnitudes.append(datapoint['magnitude_mean'])
         magnitude_vars.append(datapoint['magnitude_var'])
-       
+
+    magnitudes_db = [ 20* math.log10(x) for x in magnitudes ]
+    #approximate formula for small errors (linear approximation)
+    magnitude_vars_db = [ 20 / math.log(10) * dx/x for x, dx in zip( magnitudes,  magnitude_vars )]
+
     fig, ax1 = plt.subplots()
+
+    plt.title('Temperature sweep at ' +str(humidity) + ' % r.h.')
+
     ax1.errorbar(temps,phases,phase_vars,marker='+',linewidth=0)
     ax1.set_xlabel('temperature [deg C]')
     ax1.set_ylabel('S21 phase [deg]', color='blue')
 
     ax2 = ax1.twinx()
-    ax2.errorbar(temps,magnitudes,magnitude_vars,marker='x',color='red',linewidth=0)
-    ax2.set_ylabel('S21 magnitude [lin]', color='red')
+    ax2.errorbar(temps,magnitudes_db,magnitude_vars_db,marker='x',color='red',linewidth=0)
+    ax2.set_ylabel('S21 magnitude [dB]', color='red')
     
     fig.tight_layout()  # otherwise the right y-label is slightly clipped
     plt.show()