Added Calibration utility

for more details please see README.md file

Author: Ladislav Foldyna

utils/calibration/README.md

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+Based on the measurement, Analyzer did not provide accurate SWR results. The raw SWR
+was very dependent on frequency and did not match an expected SWR.
+
+The raw SWR samples are shown below:
+
+Freq[Hz]/Expected SWR		1	1,5	2	3	4	7,8	20
+3000000				1,00517	1,14305	1,55263	2,43736	3,28571	6,40952	16,12222
+7000000				1,00504	1,14516	1,53968	2,38526	3,15544	5,93103	13,83333
+9000000				1,00482	1,15789	1,53251	2,32927	3,07463	5,6129	11,98413
+10500000			1,00442	1,14634	1,49639	2,24953	2,92593	5,20588	10,2755
+11500000			1,0042	1,13889	1,46739	2,14992	2,76547	4,77483	8,95402
+14000000			1,00386	1,1346	1,41396	1,97744	2,47143	3,88776	6,27692
+21000000			1,00377	1,1477	1,40177	1,90788	2,3211	3,41633	5,03364
+28000000			5,8951	1,1529	1,43052	2,02791	2,48699	3,83	5,8951
+
+Therefore a calibration is highly recommended. It was tested many interpolation techniques with
+various results. Very negative think was a strong frequency dependence. Therefore the
+Antenna analyzer bandwidth (1-30MHz) was divided into the chunks - 30 chunks; 1per 1MHz
+
+After bandwidth splitting, it was possible to analyze the SWR curve and find a technique
+for computing real (expected) SWR from raw SWR. The best interpolation result returned a polynominal
+function order 3
+
+Folowing formula shows how the rela SWR is computed by Antenna Analyzer.
+
+real SWR = coef3 * RAW_SWR^3 + coef2 * RAW_SWR^2 + coef1 * RAW_SWR + con
+
+where coef3..1 and con are pre-computed values for each chunk. The coefficients are computed by calibration.py
+and have to be copy&pasted to arduino source code.
+
+What does the utility calibration.py do:
+
+1) calibration.py connects the Antenna Analyzer
+2) User is asked to enter a calibration Load
+   example "500" means: user has connected 500 Ohm dummy load and calibration can start
+3) calibration.py receives SWR values from Antenna Analyzer for every bandwidth chunk
+4) User should repeat steps 2 and 3 with various dummy loads - recommended dummy load range is 50 - 1000 Ohm
+5) If user enters an empty string then the utility computes the coefficients.
+6) The coefficients are printed as C-array initialization structure.
+7) The C-array initialization structure has to be copy&pasted to arduino source code - initialization part
+8) The arduino source code has to be compiled and uploaded to Arduino.
+

utils/calibration/calibration.py

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+#!/usr/bin/env python3
+
+# Setup script for calibration Antenna Analyzer project
+# the result should has to be inserted to Arduino source code
+
+# Usage
+#   ./calibration.py <COM_Port>
+#
+# Copyright (C) 2018 Ladislav Foldyna
+# Author: Ladislav Foldyna
+
+# This file is part of AntennaAnalyzer.
+#
+# AntennaAnalyzer is free software: you can redistribute it and/or modify
+# it under the terms of either the Apache Software License, version 2, or
+# the GNU Lesser General Public License as published by the Free Software
+# Foundation, version 3 or above.
+#
+# AntennaAnalyzer is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# You should have received a copy of both the GNU Lesser General Public
+# License and the Apache Software License. If not,
+# see <http://www.gnu.org/licenses/> and <http://www.apache.org/licenses/>.
+
+import sys
+import serial
+import numpy as np
+
+def main():
+   all_samples = [];
+
+   if ( len(sys.argv) < 2 ):
+      sys.stderr.write('Usage: {} COM_PORT\n'.format(sys.argv[0]));
+      sys.exit(1);
+
+   com_port = sys.argv[1]
+
+   try:
+      ser = serial.Serial(com_port, 57600)
+   except serial.SerialException as e:
+      sys.stderr.write('Could not open serial port {}: {}\n'.format(com_port, e))
+      sys.exit(1);
+
+   # when client establich an connection to arduino, arduino resets itself
+   # we will read booting characters but they are not important for calibration
+
+   try:
+      while True:
+         arduino_answer = str(ser.readline(), 'utf-8').rstrip()
+         print(arduino_answer)
+         if ( arduino_answer.find('#OK#') >= 0 ):
+            break;
+
+      # now calibration loop is starting
+      while True:
+         command = input("Enter Calibration Load: ")
+
+         if (len(command) == 0 ):
+            break;
+
+         command = command + 'f'
+
+         #sending user command
+         ser.write(command.encode())
+
+         run_results = []
+
+         #reading SWR calibration samples
+         # format is: <expected, frequency, raw_swr>
+         while True:
+            arduino_answer = str(ser.readline(), 'utf-8').rstrip()
+            print(arduino_answer)
+            if ( arduino_answer.find('#OK#') >= 0 ):
+               break;
+            expected_swr, freq, swr = arduino_answer.split(',')
+            run_results.append([float(expected_swr), int(freq), float(swr)])
+
+         all_samples.append(run_results)
+   except serial.SerialException as e:
+      sys.stderr.write('Communication error {}\n'.format(e))
+      sys.exit(1)
+
+   #computing the coefficients
+   for i in range(0,30):
+      x = [b[2] for b in [item[i] for item in all_samples]]
+      y = [b[0] for b in [item[i] for item in all_samples]]
+      z = np.polyfit(x,y,3)
+      print("{ .do_correction = 1, .coef3 = %f, .coef2 = %f, .coef1 = %f, .con = %f}," % (z[0], z[1], z[2], z[3]) )
+
+if __name__ == '__main__':
+   main()