Chapter 10 :Photonic Switching

Example 10.1 , Page no:183

import math
from __future__ import division

#initialisation of variables
Xx=-30;  #crosstalk in dB
L=0.3;  #typical value
N=5;  #no. of switches Nb+Nc

#CALCULATIONS
SXR=Xx-L*(N)-10*math.log10(5*(10**(-L*N/10))/N);  #Signal power to noise power in dB

#RESULTS
print"Minimum and maximum SXR values=",round(SXR,5),"dB";

Minimum and maximum SXR values= -30.0 dB

Example 10.2 , Page no:183

import math
from __future__ import division

#initialisation of variables
PB=40;  #power budget in dB
x=-30;  #crosstalk in dB assumed
N=4;  #no. of switches 
Lin=1;  #insertion loss of in dB
Linw=Lin*N;  #worst case insertion loss of in dB
Lc=2;  #worst case connector loss in dB

#CALCULATIONS
L=Linw+2*Lc;  #total power lost in the worst case signal path in dB
Power_margin=PB-L;  #power margin in dB
K=0;
for i in range (0,4):
    K=K+(((-1)**(i+1))*(10**(-x/10))**(i+1));

SbyN=10*math.log10(K);  #Signal power to noise power in dB

#RESULTS
print"Signal power to noise power =",round(SbyN,5),"dB";
print"Power Margin =",round(Power_margin,5),"dB";
print"The Textbook answer is wrong";

Signal power to noise power = 119.99566 dB
Power Margin = 32.0 dB
The Textbook answer is wrong