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# C/N and (C+N)/N

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 satnew Member ★★ Offline Posts: 23 Nov 25th, 2009 at 7:26am   Hi,  Please help. May i know the difference between (Co + No)/No and C/N? how do you convert from one another and relationship?  Please correct me if im wrong..am i looking at C/N on a spectrum analyzer when i have my marker noise on from the noise floor to the top of the carrier?thnx Back to top « Last Edit: Nov 25th, 2009 at 12:36pm by Admin1 »     IP Logged
 Eric Johnston Senior Member ★★★ Offline Posts: 2109 Reply #1 - Nov 25th, 2009 at 8:00am   Make sure the spectrum analyser resolution bandwidth is significantly less then the carrier bandwidth.Use this page EbNo calculator to calculate the C/N starting with (C+N)/N.  Just set FEC=1 and Bits/Symbol=1.When your marker is on top of the carrier you are measuring C+N.   When your marker is on the noise floor you are measuring NThe difference between the two is (C+N)/N.If you set "Marker Noise function ON" you are measuring (Co+No) or No.  The analyser works out the power per Hz knowing what is the noise bandwidth of the internal resolution bandwidth filter (ie. - 10 * log(-3dB bandwidth in Hz) - 0.5 dB).  It also corrects for noise not being like a sinewave (+2.5 dB).  Normally an analyser detector measures peak voltage and displays RMS value, assuming a sinewave input.   Noise has a different peak to mean ratio from sinewave so display value is wrong unless you do "MKR NOISE ON".A scrambled digital carrier is "noise like".If you see a 3 dB high hump in the noise floor the carrier level and the noise level are the same and add together to make twice, so C/N=0 dB and (C+N)/N = 3 dB.If you see a 20 dB (or higher) high hump in the noise floor then  C/N is about the same as (C+N)/N.For intermediate values use the calculator.Read more: HP application Note 150 (3.4 Mbytes pdf. print out 67 pages, pages 31 - 33 refer)Best regards, Eric. Back to top « Last Edit: Nov 25th, 2009 at 11:09am by Eric Johnston »     IP Logged
 satnew Member ★★ Offline Posts: 23 Reply #2 - Nov 25th, 2009 at 9:16am   hi eric,  many thanks.  will check Back to top IP Logged
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