How can I create a 'Max Hold' in Python on the Moku:Lab Spectrum Analyzer

The Moku:Lab's Spectrum Analyzer includes a math channel on both the iPad and Windows app. This math channel has a useful 'max hold' function.

The attached Python script deploys a Spectrum Analyzer instrument, sweeps the frequency and captures this data into Python. Within Python, we then calculate and display a 'Max Hold' trace.

#
# pymoku example: Plotting Spectrum Analyzer - Max Hold
#
# This example demonstrates how you can configure the Spectrum Analyzer
# instrument and plot ad Max Hold of its spectrum data in real-time. 
#
# (c) 2019 Liquid Instruments Pty. Ltd.
#
from pymoku import Moku
from pymoku.instruments import SpectrumAnalyzer
import logging
import numpy as np


import matplotlib.pyplot as plt
from matplotlib.ticker import FuncFormatter


logging.basicConfig(format='%(asctime)s:%(name)s:%(levelname)s::%(message)s')
logging.getLogger('pymoku').setLevel(logging.INFO)


# Connect to your Moku by its device name
# Alternatively, use Moku.get_by_serial('#####') or Moku('192.168.###.###')
m = Moku('192.168.1.44')


# Use dBm scaling on the y-axis
dbm = True


try:
    i = m.deploy_or_connect(SpectrumAnalyzer)


    # Set spectrum analyzer configuration
    i.set_defaults()
    i.set_dbmscale(dbm)
    i.set_span(70e6, 130e6)
    i.set_rbw()  # Auto-mode




    # Configure ADC inputs
    i.set_frontend(1, fiftyr=True)
    i.set_frontend(2, fiftyr=True)


    # Set up basic plot configurations
    line1, = plt.plot([])
    line2, = plt.plot([])
    plt.ion()
    plt.show()
    plt.grid(b=True)
    if(dbm):
        plt.ylim([-200, 100])
    else:
        plt.ylim([-0.5, 1.0])
    plt.autoscale(axis='x', tight=True)


    # Get an initial frame of data to set any frame-specific plot parameters
    frame = i.get_realtime_data()


    # Format the x-axis as a frequency scale
    ax = plt.gca()
    ax.xaxis.set_major_formatter(FuncFormatter(frame.get_xaxis_fmt))
    ax.yaxis.set_major_formatter(FuncFormatter(frame.get_yaxis_fmt))
    ax.fmt_xdata = frame.get_xcoord_fmt
    ax.fmt_ydata = frame.get_ycoord_fmt
    
    counter = 0
    spectrum_length = len(frame.ch1)
    


    # Get and update the plot with new data
    while True:
        frame = i.get_realtime_data()
        plt.pause(0.0001)
        # Set the frame data for each channel plot
        line1.set_ydata(frame.ch1)
        if counter == 0:
            current_max = frame.ch1
        else:
            for x in range(0,spectrum_length):
                if frame.ch1[x]>current_max[x]:
                    current_max[x] = frame.ch1[x]
        line2.set_ydata(current_max)        
        # Frequency axis shouldn't change, but to be sure
        line1.set_xdata(frame.frequency)
        line2.set_xdata(frame.frequency)
        # Ensure the frequency axis is a tight fit
        ax.relim()
        ax.autoscale_view()


        # Redraw the lines
        plt.draw()
        counter = counter + 1
        
finally:
    m.close()