Question

(4 points) The RS-232 port on a PC transmits data at 38.4 kbps using polar NRZ line code. What is the null to null bandwidth for this signal? What is the rate (as a function of frequency f) at which the power spectrum falls off? Can you suggest a strategy to increase the spectrum roll off rate to reduce out of band radiation?

Answer 1

SOLUTION:-

$\rightarrow$ Null to null bandwidth = + RHZ

= bit rate

= 38.4 KHZ

$\rightarrow$ The PSD of NRZ polar line coding with equally likely bits is given by

$S(f)=V^{2}T\left [ \frac{sin \Pi FT}{\Pi FT} \right ]^{2}$

When the probability of 1 is P, and O is not 0.5, a dc component exists and the PSD becomes

s(f) = 4VTP(1-P) [SinIIFT? + Vº(1-2)2s(F) IIFT

Note:- +1 $\rightarrow$ +V volts }

0 $\rightarrow$ -V volts } representation for NRZ

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